diff --git a/Android.bp b/Android.bp
new file mode 100644
index 0000000..dbc02e9
--- /dev/null
+++ b/Android.bp
@@ -0,0 +1,54 @@
+// This file is generated by cargo2android.py --config cargo2android.json.
+// Do not modify this file as changes will be overridden on upgrade.
+
+
+
+package {
+    default_applicable_licenses: ["external_rust_crates_pest_meta_license"],
+}
+
+// Added automatically by a large-scale-change that took the approach of
+// 'apply every license found to every target'. While this makes sure we respect
+// every license restriction, it may not be entirely correct.
+//
+// e.g. GPL in an MIT project might only apply to the contrib/ directory.
+//
+// Please consider splitting the single license below into multiple licenses,
+// taking care not to lose any license_kind information, and overriding the
+// default license using the 'licenses: [...]' property on targets as needed.
+//
+// For unused files, consider creating a 'fileGroup' with "//visibility:private"
+// to attach the license to, and including a comment whether the files may be
+// used in the current project.
+//
+// large-scale-change included anything that looked like it might be a license
+// text as a license_text. e.g. LICENSE, NOTICE, COPYING etc.
+//
+// Please consider removing redundant or irrelevant files from 'license_text:'.
+// See: http://go/android-license-faq
+license {
+    name: "external_rust_crates_pest_meta_license",
+    visibility: [":__subpackages__"],
+    license_kinds: [
+        "SPDX-license-identifier-Apache-2.0",
+        "SPDX-license-identifier-MIT",
+    ],
+    license_text: [
+        "LICENSE-APACHE",
+        "LICENSE-MIT",
+    ],
+}
+
+rust_library_host {
+    name: "libpest_meta",
+    // has rustc warnings
+    crate_name: "pest_meta",
+    cargo_env_compat: true,
+    cargo_pkg_version: "2.1.3",
+    srcs: ["src/lib.rs"],
+    edition: "2015",
+    rustlibs: [
+        "libpest",
+    ],
+    compile_multilib: "first",
+}
diff --git a/Cargo.toml b/Cargo.toml
new file mode 100644
index 0000000..74f8377
--- /dev/null
+++ b/Cargo.toml
@@ -0,0 +1,42 @@
+# THIS FILE IS AUTOMATICALLY GENERATED BY CARGO
+#
+# When uploading crates to the registry Cargo will automatically
+# "normalize" Cargo.toml files for maximal compatibility
+# with all versions of Cargo and also rewrite `path` dependencies
+# to registry (e.g., crates.io) dependencies
+#
+# If you believe there's an error in this file please file an
+# issue against the rust-lang/cargo repository. If you're
+# editing this file be aware that the upstream Cargo.toml
+# will likely look very different (and much more reasonable)
+
+[package]
+name = "pest_meta"
+version = "2.1.3"
+authors = ["Dragoș Tiselice <dragostiselice@gmail.com>"]
+exclude = ["src/grammar.pest"]
+include = ["Cargo.toml", "src/**/*", "src/grammar.rs", "_README.md", "LICENSE-*"]
+description = "pest meta language parser and validator"
+homepage = "https://pest-parser.github.io/"
+documentation = "https://docs.rs/pest"
+readme = "_README.md"
+keywords = ["pest", "parser", "meta", "optimizer"]
+categories = ["parsing"]
+license = "MIT/Apache-2.0"
+repository = "https://github.com/pest-parser/pest"
+[dependencies.maplit]
+version = "1.0"
+
+[dependencies.pest]
+version = "2.1.0"
+[build-dependencies.sha-1]
+version = "0.8"
+default-features = false
+[badges.codecov]
+repository = "pest-parser/pest"
+
+[badges.maintenance]
+status = "actively-developed"
+
+[badges.travis-ci]
+repository = "pest-parser/pest"
diff --git a/Cargo.toml.orig b/Cargo.toml.orig
new file mode 100644
index 0000000..40c7570
--- /dev/null
+++ b/Cargo.toml.orig
@@ -0,0 +1,26 @@
+[package]
+name = "pest_meta"
+description = "pest meta language parser and validator"
+version = "2.1.3"
+authors = ["Dragoș Tiselice <dragostiselice@gmail.com>"]
+homepage = "https://pest-parser.github.io/"
+repository = "https://github.com/pest-parser/pest"
+documentation = "https://docs.rs/pest"
+keywords = ["pest", "parser", "meta", "optimizer"]
+categories = ["parsing"]
+license = "MIT/Apache-2.0"
+readme = "_README.md"
+exclude = ["src/grammar.pest"]
+include = ["Cargo.toml", "src/**/*", "src/grammar.rs", "_README.md", "LICENSE-*"]
+
+[dependencies]
+maplit = "1.0"
+pest = { path = "../pest", version = "2.1.0" }
+
+[badges]
+codecov = { repository = "pest-parser/pest" }
+maintenance = { status = "actively-developed" }
+travis-ci = { repository = "pest-parser/pest" }
+
+[build-dependencies]
+sha-1 = { version = "0.8", default-features = false }
diff --git a/LICENSE b/LICENSE
new file mode 120000
index 0000000..6b579aa
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1 @@
+LICENSE-APACHE
\ No newline at end of file
diff --git a/LICENSE-APACHE b/LICENSE-APACHE
new file mode 100644
index 0000000..16fe87b
--- /dev/null
+++ b/LICENSE-APACHE
@@ -0,0 +1,201 @@
+                              Apache License
+                        Version 2.0, January 2004
+                     http://www.apache.org/licenses/
+
+TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION
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+   any Contribution intentionally submitted for inclusion in the Work
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+6. Trademarks. This License does not grant permission to use the trade
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diff --git a/LICENSE-MIT b/LICENSE-MIT
new file mode 100644
index 0000000..31aa793
--- /dev/null
+++ b/LICENSE-MIT
@@ -0,0 +1,23 @@
+Permission is hereby granted, free of charge, to any
+person obtaining a copy of this software and associated
+documentation files (the "Software"), to deal in the
+Software without restriction, including without
+limitation the rights to use, copy, modify, merge,
+publish, distribute, sublicense, and/or sell copies of
+the Software, and to permit persons to whom the Software
+is furnished to do so, subject to the following
+conditions:
+
+The above copyright notice and this permission notice
+shall be included in all copies or substantial portions
+of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF
+ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED
+TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
+PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT
+SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR
+IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+DEALINGS IN THE SOFTWARE.
diff --git a/METADATA b/METADATA
new file mode 100644
index 0000000..7a2a522
--- /dev/null
+++ b/METADATA
@@ -0,0 +1,20 @@
+name: "pest_meta"
+description: "pest meta language parser and validator"
+third_party {
+  url {
+    type: HOMEPAGE
+    value: "https://crates.io/crates/pest_meta"
+  }
+  url {
+    type: ARCHIVE
+    value: "https://static.crates.io/crates/pest_meta/pest_meta-2.1.3.crate"
+  }
+  version: "2.1.3"
+  # Dual-licensed, using the least restrictive per go/thirdpartylicenses#same.
+  license_type: NOTICE
+  last_upgrade_date {
+    year: 2022
+    month: 1
+    day: 27
+  }
+}
diff --git a/MODULE_LICENSE_APACHE2 b/MODULE_LICENSE_APACHE2
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/MODULE_LICENSE_APACHE2
diff --git a/OWNERS b/OWNERS
new file mode 100644
index 0000000..45dc4dd
--- /dev/null
+++ b/OWNERS
@@ -0,0 +1 @@
+include platform/prebuilts/rust:master:/OWNERS
diff --git a/_README.md b/_README.md
new file mode 100644
index 0000000..8e55f29
--- /dev/null
+++ b/_README.md
@@ -0,0 +1,169 @@
+<p align="center">
+  <img src="https://raw.github.com/pest-parser/pest/master/pest-logo.svg?sanitize=true" width="80%"/>
+</p>
+
+# pest. The Elegant Parser
+
+[![Join the chat at https://gitter.im/dragostis/pest](https://badges.gitter.im/dragostis/pest.svg)](https://gitter.im/dragostis/pest?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
+[![Book](https://img.shields.io/badge/book-WIP-4d76ae.svg)](https://pest-parser.github.io/book)
+[![Docs](https://docs.rs/pest/badge.svg)](https://docs.rs/pest)
+
+[![Build Status](https://travis-ci.org/pest-parser/pest.svg?branch=master)](https://travis-ci.org/pest-parser/pest)
+[![codecov](https://codecov.io/gh/pest-parser/pest/branch/master/graph/badge.svg)](https://codecov.io/gh/pest-parser/pest)
+[![Fuzzit Status](https://app.fuzzit.dev/badge?org_id=pest-parser)](https://app.fuzzit.dev/orgs/pest-parser/dashboard)
+[![Crates.io](https://img.shields.io/crates/d/pest.svg)](https://crates.io/crates/pest)
+[![Crates.io](https://img.shields.io/crates/v/pest.svg)](https://crates.io/crates/pest)
+
+pest is a general purpose parser written in Rust with a focus on accessibility,
+correctness, and performance. It uses parsing expression grammars
+(or [PEG]) as input, which are similar in spirit to regular expressions, but
+which offer the enhanced expressivity needed to parse complex languages.
+
+[PEG]: https://en.wikipedia.org/wiki/Parsing_expression_grammar
+
+## Getting started
+
+The recommended way to start parsing with pest is to read the official [book].
+
+Other helpful resources:
+
+* API reference on [docs.rs]
+* play with grammars and share them on our [fiddle]
+* leave feedback, ask questions, or greet us on [Gitter]
+
+[book]: https://pest-parser.github.io/book
+[docs.rs]: https://docs.rs/pest
+[fiddle]: https://pest-parser.github.io/#editor
+[Gitter]: https://gitter.im/dragostis/pest
+
+## Example
+
+The following is an example of a grammar for a list of alpha-numeric identifiers
+where the first identifier does not start with a digit:
+
+```rust
+alpha = { 'a'..'z' | 'A'..'Z' }
+digit = { '0'..'9' }
+
+ident = { (alpha | digit)+ }
+
+ident_list = _{ !digit ~ ident ~ (" " ~ ident)+ }
+          // ^
+          // ident_list rule is silent which means it produces no tokens
+```
+
+Grammars are saved in separate .pest files which are never mixed with procedural
+code. This results in an always up-to-date formalization of a language that is
+easy to read and maintain.
+
+## Meaningful error reporting
+
+Based on the grammar definition, the parser also includes automatic error
+reporting. For the example above, the input `"123"` will result in:
+
+```
+thread 'main' panicked at ' --> 1:1
+  |
+1 | 123
+  | ^---
+  |
+  = unexpected digit', src/main.rs:12
+```
+while `"ab *"` will result in:
+```
+thread 'main' panicked at ' --> 1:1
+  |
+1 | ab *
+  |    ^---
+  |
+  = expected ident', src/main.rs:12
+```
+
+## Pairs API
+
+The grammar can be used to derive a `Parser` implementation automatically.
+Parsing returns an iterator of nested token pairs:
+
+```rust
+extern crate pest;
+#[macro_use]
+extern crate pest_derive;
+
+use pest::Parser;
+
+#[derive(Parser)]
+#[grammar = "ident.pest"]
+struct IdentParser;
+
+fn main() {
+    let pairs = IdentParser::parse(Rule::ident_list, "a1 b2").unwrap_or_else(|e| panic!("{}", e));
+
+    // Because ident_list is silent, the iterator will contain idents
+    for pair in pairs {
+        // A pair is a combination of the rule which matched and a span of input
+        println!("Rule:    {:?}", pair.as_rule());
+        println!("Span:    {:?}", pair.as_span());
+        println!("Text:    {}", pair.as_str());
+
+        // A pair can be converted to an iterator of the tokens which make it up:
+        for inner_pair in pair.into_inner() {
+            match inner_pair.as_rule() {
+                Rule::alpha => println!("Letter:  {}", inner_pair.as_str()),
+                Rule::digit => println!("Digit:   {}", inner_pair.as_str()),
+                _ => unreachable!()
+            };
+        }
+    }
+}
+```
+
+This produces the following output:
+```
+Rule:    ident
+Span:    Span { start: 0, end: 2 }
+Text:    a1
+Letter:  a
+Digit:   1
+Rule:    ident
+Span:    Span { start: 3, end: 5 }
+Text:    b2
+Letter:  b
+Digit:   2
+```
+
+## Other features
+
+* Precedence climbing
+* Input handling
+* Custom errors
+* Runs on stable Rust
+
+## Projects using pest
+
+* [pest_meta](https://github.com/pest-parser/pest/blob/master/meta/src/grammar.pest) (bootstrapped)
+* [AshPaper](https://github.com/shnewto/ashpaper)
+* [brain](https://github.com/brain-lang/brain)
+* [Chelone](https://github.com/Aaronepower/chelone)
+* [comrak](https://github.com/kivikakk/comrak)
+* [elastic-rs](https://github.com/cch123/elastic-rs)
+* [graphql-parser](https://github.com/Keats/graphql-parser)
+* [handlebars-rust](https://github.com/sunng87/handlebars-rust)
+* [hexdino](https://github.com/Luz/hexdino)
+* [Huia](https://gitlab.com/jimsy/huia/)
+* [jql](https://github.com/yamafaktory/jql)
+* [json5-rs](https://github.com/callum-oakley/json5-rs)
+* [mt940](https://github.com/svenstaro/mt940-rs)
+* [py_literal](https://github.com/jturner314/py_literal)
+* [rouler](https://github.com/jarcane/rouler)
+* [RuSh](https://github.com/lwandrebeck/RuSh)
+* [rs_pbrt](https://github.com/wahn/rs_pbrt)
+* [stache](https://github.com/dgraham/stache)
+* [tera](https://github.com/Keats/tera)
+* [ui_gen](https://github.com/emoon/ui_gen)
+* [ukhasnet-parser](https://github.com/adamgreig/ukhasnet-parser)
+* [ZoKrates](https://github.com/ZoKrates/ZoKrates)
+
+## Special thanks
+
+A special round of applause goes to prof. Marius Minea for his guidance and all
+pest contributors, some of which being none other than my friends.
diff --git a/cargo2android.json b/cargo2android.json
new file mode 100644
index 0000000..833343e
--- /dev/null
+++ b/cargo2android.json
@@ -0,0 +1,5 @@
+{
+  "patch": "patches/Android.bp.diff",
+  "run": true,
+  "host-first-multilib": true
+}
diff --git a/patches/0001-Remove-unused-extern-crate-maplit.patch b/patches/0001-Remove-unused-extern-crate-maplit.patch
new file mode 100644
index 0000000..abcf752
--- /dev/null
+++ b/patches/0001-Remove-unused-extern-crate-maplit.patch
@@ -0,0 +1,25 @@
+From cca209337abe86ad35dc705dd293b1ab264f5e46 Mon Sep 17 00:00:00 2001
+From: Henri Chataing <henrichataing@google.com>
+Date: Fri, 18 Feb 2022 11:49:59 +0100
+Subject: [PATCH] Remove unused extern crate maplit
+
+Change-Id: I4fdf3fb28528ba228d3c4869c7a4a17921f8293d
+---
+ src/lib.rs | 1 -
+ 1 file changed, 1 deletion(-)
+
+diff --git a/src/lib.rs b/src/lib.rs
+index 1f9c5bc..28f33b0 100644
+--- a/src/lib.rs
++++ b/src/lib.rs
+@@ -9,7 +9,6 @@
+ 
+ #![allow(clippy::range_plus_one)]
+ 
+-extern crate maplit;
+ #[cfg(test)]
+ #[macro_use]
+ extern crate pest;
+-- 
+2.35.1.265.g69c8d7142f-goog
+
diff --git a/patches/Android.bp.diff b/patches/Android.bp.diff
new file mode 100644
index 0000000..14c6cb9
--- /dev/null
+++ b/patches/Android.bp.diff
@@ -0,0 +1,12 @@
+diff --git a/Android.bp b/Android.bp
+index 62e8f1f..691d848 100644
+--- a/Android.bp
++++ b/Android.bp
+@@ -12,7 +12,6 @@ rust_library_host {
+     srcs: ["src/lib.rs"],
+     edition: "2015",
+     rustlibs: [
+-        "libmaplit",
+         "libpest",
+     ],
+     compile_multilib: "first",
diff --git a/src/ast.rs b/src/ast.rs
new file mode 100644
index 0000000..b80c596
--- /dev/null
+++ b/src/ast.rs
@@ -0,0 +1,315 @@
+// pest. The Elegant Parser
+// Copyright (c) 2018 Dragoș Tiselice
+//
+// Licensed under the Apache License, Version 2.0
+// <LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0> or the MIT
+// license <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. All files in the project carrying such notice may not be copied,
+// modified, or distributed except according to those terms.
+
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub struct Rule {
+    pub name: String,
+    pub ty: RuleType,
+    pub expr: Expr,
+}
+
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+pub enum RuleType {
+    Normal,
+    Silent,
+    Atomic,
+    CompoundAtomic,
+    NonAtomic,
+}
+
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub enum Expr {
+    /// Matches an exact string, e.g. `"a"`
+    Str(String),
+    /// Matches an exact string, case insensitively (ASCII only), e.g. `^"a"`
+    Insens(String),
+    /// Matches one character in the range, e.g. `'a'..'z'`
+    Range(String, String),
+    /// Matches the rule with the given name, e.g. `a`
+    Ident(String),
+    /// Matches a custom part of the stack, e.g. `PEEK[..]`
+    PeekSlice(i32, Option<i32>),
+    /// Positive lookahead; matches expression without making progress, e.g. `&e`
+    PosPred(Box<Expr>),
+    /// Negative lookahead; matches if expression doesn't match, without making progress, e.g. `!e`
+    NegPred(Box<Expr>),
+    /// Matches a sequence of two expressions, e.g. `e1 ~ e2`
+    Seq(Box<Expr>, Box<Expr>),
+    /// Matches either of two expressions, e.g. `e1 | e2`
+    Choice(Box<Expr>, Box<Expr>),
+    /// Optionally matches an expression, e.g. `e?`
+    Opt(Box<Expr>),
+    /// Matches an expression zero or more times, e.g. `e*`
+    Rep(Box<Expr>),
+    /// Matches an expression one or more times, e.g. `e+`
+    RepOnce(Box<Expr>),
+    /// Matches an expression an exact number of times, e.g. `e{n}`
+    RepExact(Box<Expr>, u32),
+    /// Matches an expression at least a number of times, e.g. `e{n,}`
+    RepMin(Box<Expr>, u32),
+    /// Matches an expression at most a number of times, e.g. `e{,n}`
+    RepMax(Box<Expr>, u32),
+    /// Matches an expression a number of times within a range, e.g. `e{m, n}`
+    RepMinMax(Box<Expr>, u32, u32),
+    /// Continues to match expressions until one of the strings in the `Vec` is found
+    Skip(Vec<String>),
+    /// Matches an expression and pushes it to the stack, e.g. `push(e)`
+    Push(Box<Expr>),
+}
+
+impl Expr {
+    pub fn iter_top_down(&self) -> ExprTopDownIterator {
+        ExprTopDownIterator::new(self)
+    }
+
+    pub fn map_top_down<F>(self, mut f: F) -> Expr
+    where
+        F: FnMut(Expr) -> Expr,
+    {
+        fn map_internal<F>(expr: Expr, f: &mut F) -> Expr
+        where
+            F: FnMut(Expr) -> Expr,
+        {
+            let expr = f(expr);
+
+            match expr {
+                // TODO: Use box syntax when it gets stabilized.
+                Expr::PosPred(expr) => {
+                    let mapped = Box::new(map_internal(*expr, f));
+                    Expr::PosPred(mapped)
+                }
+                Expr::NegPred(expr) => {
+                    let mapped = Box::new(map_internal(*expr, f));
+                    Expr::NegPred(mapped)
+                }
+                Expr::Seq(lhs, rhs) => {
+                    let mapped_lhs = Box::new(map_internal(*lhs, f));
+                    let mapped_rhs = Box::new(map_internal(*rhs, f));
+                    Expr::Seq(mapped_lhs, mapped_rhs)
+                }
+                Expr::Choice(lhs, rhs) => {
+                    let mapped_lhs = Box::new(map_internal(*lhs, f));
+                    let mapped_rhs = Box::new(map_internal(*rhs, f));
+                    Expr::Choice(mapped_lhs, mapped_rhs)
+                }
+                Expr::Rep(expr) => {
+                    let mapped = Box::new(map_internal(*expr, f));
+                    Expr::Rep(mapped)
+                }
+                Expr::RepOnce(expr) => {
+                    let mapped = Box::new(map_internal(*expr, f));
+                    Expr::RepOnce(mapped)
+                }
+                Expr::RepExact(expr, max) => {
+                    let mapped = Box::new(map_internal(*expr, f));
+                    Expr::RepExact(mapped, max)
+                }
+                Expr::RepMin(expr, num) => {
+                    let mapped = Box::new(map_internal(*expr, f));
+                    Expr::RepMin(mapped, num)
+                }
+                Expr::RepMax(expr, num) => {
+                    let mapped = Box::new(map_internal(*expr, f));
+                    Expr::RepMax(mapped, num)
+                }
+                Expr::RepMinMax(expr, min, max) => {
+                    let mapped = Box::new(map_internal(*expr, f));
+                    Expr::RepMinMax(mapped, min, max)
+                }
+                Expr::Opt(expr) => {
+                    let mapped = Box::new(map_internal(*expr, f));
+                    Expr::Opt(mapped)
+                }
+                Expr::Push(expr) => {
+                    let mapped = Box::new(map_internal(*expr, f));
+                    Expr::Push(mapped)
+                }
+                expr => expr,
+            }
+        }
+
+        map_internal(self, &mut f)
+    }
+
+    pub fn map_bottom_up<F>(self, mut f: F) -> Expr
+    where
+        F: FnMut(Expr) -> Expr,
+    {
+        fn map_internal<F>(expr: Expr, f: &mut F) -> Expr
+        where
+            F: FnMut(Expr) -> Expr,
+        {
+            let mapped = match expr {
+                Expr::PosPred(expr) => {
+                    // TODO: Use box syntax when it gets stabilized.
+                    let mapped = Box::new(map_internal(*expr, f));
+                    Expr::PosPred(mapped)
+                }
+                Expr::NegPred(expr) => {
+                    let mapped = Box::new(map_internal(*expr, f));
+                    Expr::NegPred(mapped)
+                }
+                Expr::Seq(lhs, rhs) => {
+                    let mapped_lhs = Box::new(map_internal(*lhs, f));
+                    let mapped_rhs = Box::new(map_internal(*rhs, f));
+                    Expr::Seq(mapped_lhs, mapped_rhs)
+                }
+                Expr::Choice(lhs, rhs) => {
+                    let mapped_lhs = Box::new(map_internal(*lhs, f));
+                    let mapped_rhs = Box::new(map_internal(*rhs, f));
+                    Expr::Choice(mapped_lhs, mapped_rhs)
+                }
+                Expr::Rep(expr) => {
+                    let mapped = Box::new(map_internal(*expr, f));
+                    Expr::Rep(mapped)
+                }
+                Expr::RepOnce(expr) => {
+                    let mapped = Box::new(map_internal(*expr, f));
+                    Expr::RepOnce(mapped)
+                }
+                Expr::RepExact(expr, num) => {
+                    let mapped = Box::new(map_internal(*expr, f));
+                    Expr::RepExact(mapped, num)
+                }
+                Expr::RepMin(expr, max) => {
+                    let mapped = Box::new(map_internal(*expr, f));
+                    Expr::RepMin(mapped, max)
+                }
+                Expr::RepMax(expr, max) => {
+                    let mapped = Box::new(map_internal(*expr, f));
+                    Expr::RepMax(mapped, max)
+                }
+                Expr::RepMinMax(expr, min, max) => {
+                    let mapped = Box::new(map_internal(*expr, f));
+                    Expr::RepMinMax(mapped, min, max)
+                }
+                Expr::Opt(expr) => {
+                    let mapped = Box::new(map_internal(*expr, f));
+                    Expr::Opt(mapped)
+                }
+                Expr::Push(expr) => {
+                    let mapped = Box::new(map_internal(*expr, f));
+                    Expr::Push(mapped)
+                }
+                expr => expr,
+            };
+
+            f(mapped)
+        }
+
+        map_internal(self, &mut f)
+    }
+}
+
+pub struct ExprTopDownIterator {
+    current: Option<Expr>,
+    next: Option<Expr>,
+    right_branches: Vec<Expr>,
+}
+
+impl ExprTopDownIterator {
+    pub fn new(expr: &Expr) -> Self {
+        let mut iter = ExprTopDownIterator {
+            current: None,
+            next: None,
+            right_branches: vec![],
+        };
+        iter.iterate_expr(expr.clone());
+        iter
+    }
+
+    fn iterate_expr(&mut self, expr: Expr) {
+        self.current = Some(expr.clone());
+        match expr {
+            Expr::Seq(lhs, rhs) => {
+                self.right_branches.push(*rhs);
+                self.next = Some(*lhs);
+            }
+            Expr::Choice(lhs, rhs) => {
+                self.right_branches.push(*rhs);
+                self.next = Some(*lhs);
+            }
+            Expr::PosPred(expr)
+            | Expr::NegPred(expr)
+            | Expr::Rep(expr)
+            | Expr::RepOnce(expr)
+            | Expr::RepExact(expr, _)
+            | Expr::RepMin(expr, _)
+            | Expr::RepMax(expr, _)
+            | Expr::RepMinMax(expr, ..)
+            | Expr::Opt(expr)
+            | Expr::Push(expr) => {
+                self.next = Some(*expr);
+            }
+            _ => {
+                self.next = None;
+            }
+        }
+    }
+}
+
+impl Iterator for ExprTopDownIterator {
+    type Item = Expr;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        let result = self.current.take();
+
+        if let Some(expr) = self.next.take() {
+            self.iterate_expr(expr);
+        } else if let Some(expr) = self.right_branches.pop() {
+            self.iterate_expr(expr);
+        }
+
+        result
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn top_down_iterator() {
+        let expr = Expr::Choice(
+            Box::new(Expr::Str(String::from("a"))),
+            Box::new(Expr::Str(String::from("b"))),
+        );
+        let mut top_down = expr.clone().iter_top_down();
+        assert_eq!(top_down.next(), Some(expr));
+        assert_eq!(top_down.next(), Some(Expr::Str(String::from("a"))));
+        assert_eq!(top_down.next(), Some(Expr::Str(String::from("b"))));
+        assert_eq!(top_down.next(), None);
+    }
+
+    #[test]
+    fn identity() {
+        let expr = Expr::Choice(
+            Box::new(Expr::Seq(
+                Box::new(Expr::Ident("a".to_owned())),
+                Box::new(Expr::Str("b".to_owned())),
+            )),
+            Box::new(Expr::PosPred(Box::new(Expr::NegPred(Box::new(Expr::Rep(
+                Box::new(Expr::RepOnce(Box::new(Expr::Opt(Box::new(Expr::Choice(
+                    Box::new(Expr::Insens("c".to_owned())),
+                    Box::new(Expr::Push(Box::new(Expr::Range(
+                        "'d'".to_owned(),
+                        "'e'".to_owned(),
+                    )))),
+                )))))),
+            )))))),
+        );
+
+        assert_eq!(
+            expr.clone()
+                .map_bottom_up(|expr| expr)
+                .map_top_down(|expr| expr),
+            expr
+        );
+    }
+}
diff --git a/src/grammar.pest b/src/grammar.pest
new file mode 100644
index 0000000..0d03ba8
--- /dev/null
+++ b/src/grammar.pest
@@ -0,0 +1,98 @@
+// pest. The Elegant Parser
+// Copyright (c) 2018 Dragoș Tiselice
+//
+// Licensed under the Apache License, Version 2.0
+// <LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0> or the MIT
+// license <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. All files in the project carrying such notice may not be copied,
+// modified, or distributed except according to those terms.
+
+grammar_rules = _{ SOI ~ grammar_rule+ ~ EOI }
+
+grammar_rule = {
+    identifier ~ assignment_operator ~ modifier? ~
+    opening_brace ~ expression ~ closing_brace
+}
+
+assignment_operator = { "=" }
+opening_brace       = { "{" }
+closing_brace       = { "}" }
+opening_paren       = { "(" }
+closing_paren       = { ")" }
+opening_brack       = { "[" }
+closing_brack       = { "]" }
+
+modifier = _{
+    silent_modifier |
+    atomic_modifier |
+    compound_atomic_modifier |
+    non_atomic_modifier
+}
+
+silent_modifier          = { "_" }
+atomic_modifier          = { "@" }
+compound_atomic_modifier = { "$" }
+non_atomic_modifier      = { "!" }
+
+expression =  { term ~ (infix_operator ~ term)* }
+term       =  { prefix_operator* ~ node ~ postfix_operator* }
+node       = _{ opening_paren ~ expression ~ closing_paren | terminal }
+terminal   = _{ _push | peek_slice | identifier | string | insensitive_string | range }
+
+prefix_operator  = _{ positive_predicate_operator | negative_predicate_operator }
+infix_operator   = _{ sequence_operator | choice_operator }
+postfix_operator = _{
+    optional_operator |
+    repeat_operator |
+    repeat_once_operator |
+    repeat_exact |
+    repeat_min |
+    repeat_max |
+    repeat_min_max
+}
+
+positive_predicate_operator = { "&" }
+negative_predicate_operator = { "!" }
+sequence_operator           = { "~" }
+choice_operator             = { "|" }
+optional_operator           = { "?" }
+repeat_operator             = { "*" }
+repeat_once_operator        = { "+" }
+
+repeat_exact   = { opening_brace ~ number ~ closing_brace }
+repeat_min     = { opening_brace ~ number ~ comma ~ closing_brace }
+repeat_max     = { opening_brace ~ comma ~ number ~ closing_brace }
+repeat_min_max = { opening_brace ~ number ~ comma ~ number ~ closing_brace }
+
+number = @{ '0'..'9'+ }
+integer = @{ number | "-" ~ "0"* ~ '1'..'9' ~ number? }
+
+comma = { "," }
+
+_push = { "PUSH" ~ opening_paren ~ expression ~ closing_paren }
+peek_slice = { "PEEK" ~ opening_brack ~ integer? ~ range_operator ~ integer? ~ closing_brack }
+
+identifier = @{ !"PUSH" ~ ("_" | alpha) ~ ("_" | alpha_num)* }
+alpha      = _{ 'a'..'z' | 'A'..'Z' }
+alpha_num  = _{ alpha | '0'..'9' }
+
+string             = ${ quote ~ inner_str ~ quote }
+insensitive_string =  { "^" ~ string }
+range              =  { character ~ range_operator ~ character }
+character          = ${ single_quote ~ inner_chr ~ single_quote }
+
+inner_str = @{ (!("\"" | "\\") ~ ANY)* ~ (escape ~ inner_str)? }
+inner_chr = @{ escape | ANY }
+escape    = @{ "\\" ~ ("\"" | "\\" | "r" | "n" | "t" | "0" | "'" | code | unicode) }
+code      = @{ "x" ~ hex_digit{2} }
+unicode   = @{ "u" ~ opening_brace ~ hex_digit{2, 6} ~ closing_brace }
+hex_digit = @{ '0'..'9' | 'a'..'f' | 'A'..'F' }
+
+quote          = { "\"" }
+single_quote   = { "'" }
+range_operator = { ".." }
+
+newline    = _{ "\n" | "\r\n" }
+WHITESPACE = _{ " " | "\t" | newline }
+block_comment = _{ "/*" ~ (block_comment | !"*/" ~ ANY)* ~ "*/" }
+COMMENT    = _{ block_comment | ("//" ~ (!newline ~ ANY)*) }
diff --git a/src/grammar.rs b/src/grammar.rs
new file mode 100644
index 0000000..bf94a1e
--- /dev/null
+++ b/src/grammar.rs
@@ -0,0 +1,2 @@
+pub struct PestParser;
+# [ allow ( dead_code , non_camel_case_types ) ] # [ derive ( Clone , Copy , Debug , Eq , Hash , Ord , PartialEq , PartialOrd ) ] pub enum Rule { EOI , grammar_rules , grammar_rule , assignment_operator , opening_brace , closing_brace , opening_paren , closing_paren , opening_brack , closing_brack , modifier , silent_modifier , atomic_modifier , compound_atomic_modifier , non_atomic_modifier , expression , term , node , terminal , prefix_operator , infix_operator , postfix_operator , positive_predicate_operator , negative_predicate_operator , sequence_operator , choice_operator , optional_operator , repeat_operator , repeat_once_operator , repeat_exact , repeat_min , repeat_max , repeat_min_max , number , integer , comma , _push , peek_slice , identifier , alpha , alpha_num , string , insensitive_string , range , character , inner_str , inner_chr , escape , code , unicode , hex_digit , quote , single_quote , range_operator , newline , WHITESPACE , block_comment , COMMENT } # [ allow ( clippy :: all ) ] impl :: pest :: Parser < Rule > for PestParser { fn parse < 'i > ( rule : Rule , input : & 'i str ) -> :: std :: result :: Result < :: pest :: iterators :: Pairs < 'i , Rule > , :: pest :: error :: Error < Rule > > { mod rules { pub mod hidden { use super :: super :: Rule ; # [ inline ] # [ allow ( dead_code , non_snake_case , unused_variables ) ] pub fn skip ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { if state . atomicity ( ) == :: pest :: Atomicity :: NonAtomic { state . sequence ( | state | { state . repeat ( | state | super :: visible :: WHITESPACE ( state ) ) . and_then ( | state | { state . repeat ( | state | { state . sequence ( | state | { super :: visible :: COMMENT ( state ) . and_then ( | state | { state . repeat ( | state | super :: visible :: WHITESPACE ( state ) ) } ) } ) } ) } ) } ) } else { Ok ( state ) } } } pub mod visible { use super :: super :: Rule ; # [ inline ] # [ allow ( non_snake_case , unused_variables ) ] pub fn grammar_rules ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { state . sequence ( | state | { self :: SOI ( state ) . and_then ( | state | { super :: hidden :: skip ( state ) } ) . and_then ( | state | { state . sequence ( | state | { self :: grammar_rule ( state ) . and_then ( | state | { super :: hidden :: skip ( state ) } ) . and_then ( | state | { state . sequence ( | state | { state . optional ( | state | { self :: grammar_rule ( state ) . and_then ( | state | { state . repeat ( | state | { state . sequence ( | state | { super :: hidden :: skip ( state ) . and_then ( | state | { self :: grammar_rule ( state ) } ) } ) } ) } ) } ) } ) } ) } ) } ) . and_then ( | state | { super :: hidden :: skip ( state ) } ) . and_then ( | state | { self :: EOI ( state ) } ) } ) } # [ inline ] # [ allow ( non_snake_case , unused_variables ) ] pub fn grammar_rule ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { state . rule ( Rule :: grammar_rule , | state | { state . sequence ( | state | { self :: identifier ( state ) . and_then ( | state | { super :: hidden :: skip ( state ) } ) . and_then ( | state | { self :: assignment_operator ( state ) } ) . and_then ( | state | { super :: hidden :: skip ( state ) } ) . and_then ( | state | { state . optional ( | state | { self :: modifier ( state ) } ) } ) . and_then ( | state | { super :: hidden :: skip ( state ) } ) . and_then ( | state | { self :: opening_brace ( state ) } ) . and_then ( | state | { super :: hidden :: skip ( state ) } ) . and_then ( | state | { self :: expression ( state ) } ) . and_then ( | state | { super :: hidden :: skip ( state ) } ) . and_then ( | state | { self :: closing_brace ( state ) } ) } ) } ) } # [ inline ] # [ allow ( non_snake_case , unused_variables ) ] pub fn assignment_operator ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { state . rule ( Rule :: assignment_operator , | state | { state . match_string ( "=" ) } ) } # [ inline ] # [ allow ( non_snake_case , unused_variables ) ] pub fn opening_brace ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { state . rule ( Rule :: opening_brace , | state | { state . match_string ( "{" ) } ) } # [ inline ] # [ allow ( non_snake_case , unused_variables ) ] pub fn closing_brace ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { state . rule ( Rule :: closing_brace , | state | { state . match_string ( "}" ) } ) } # [ inline ] # [ allow ( non_snake_case , unused_variables ) ] pub fn opening_paren ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { state . rule ( Rule :: opening_paren , | state | { state . match_string ( "(" ) } ) } # [ inline ] # [ allow ( non_snake_case , unused_variables ) ] pub fn closing_paren ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { state . rule ( Rule :: closing_paren , | state | { state . match_string ( ")" ) } ) } # [ inline ] # [ allow ( non_snake_case , unused_variables ) ] pub fn opening_brack ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { state . rule ( Rule :: opening_brack , | state | { state . match_string ( "[" ) } ) } # [ inline ] # [ allow ( non_snake_case , unused_variables ) ] pub fn closing_brack ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { state . rule ( Rule :: closing_brack , | state | { state . match_string ( "]" ) } ) } # [ inline ] # [ allow ( non_snake_case , unused_variables ) ] pub fn modifier ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { self :: silent_modifier ( state ) . or_else ( | state | { self :: atomic_modifier ( state ) } ) . or_else ( | state | { self :: compound_atomic_modifier ( state ) } ) . or_else ( | state | { self :: non_atomic_modifier ( state ) } ) } # [ inline ] # [ allow ( non_snake_case , unused_variables ) ] pub fn silent_modifier ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { state . rule ( Rule :: silent_modifier , | state | { state . match_string ( "_" ) } ) } # [ inline ] # [ allow ( non_snake_case , unused_variables ) ] pub fn atomic_modifier ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { state . rule ( Rule :: atomic_modifier , | state | { state . match_string ( "@" ) } ) } # [ inline ] # [ allow ( non_snake_case , unused_variables ) ] pub fn compound_atomic_modifier ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { state . rule ( Rule :: compound_atomic_modifier , | state | { state . match_string ( "$" ) } ) } # [ inline ] # [ allow ( non_snake_case , unused_variables ) ] pub fn non_atomic_modifier ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { state . rule ( Rule :: non_atomic_modifier , | state | { state . match_string ( "!" ) } ) } # [ inline ] # [ allow ( non_snake_case , unused_variables ) ] pub fn expression ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { state . rule ( Rule :: expression , | state | { state . sequence ( | state | { self :: term ( state ) . and_then ( | state | { super :: hidden :: skip ( state ) } ) . and_then ( | state | { state . sequence ( | state | { state . optional ( | state | { state . sequence ( | state | { self :: infix_operator ( state ) . and_then ( | state | { super :: hidden :: skip ( state ) } ) . and_then ( | state | { self :: term ( state ) } ) } ) . and_then ( | state | { state . repeat ( | state | { state . sequence ( | state | { super :: hidden :: skip ( state ) . and_then ( | state | { state . sequence ( | state | { self :: infix_operator ( state ) . and_then ( | state | { super :: hidden :: skip ( state ) } ) . and_then ( | state | { self :: term ( state ) } ) } ) } ) } ) } ) } ) } ) } ) } ) } ) } ) } # [ inline ] # [ allow ( non_snake_case , unused_variables ) ] pub fn term ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { state . rule ( Rule :: term , | state | { state . sequence ( | state | { state . sequence ( | state | { state . optional ( | state | { self :: prefix_operator ( state ) . and_then ( | state | { state . repeat ( | state | { state . sequence ( | state | { super :: hidden :: skip ( state ) . and_then ( | state | { self :: prefix_operator ( state ) } ) } ) } ) } ) } ) } ) . and_then ( | state | { super :: hidden :: skip ( state ) } ) . and_then ( | state | { self :: node ( state ) } ) . and_then ( | state | { super :: hidden :: skip ( state ) } ) . and_then ( | state | { state . sequence ( | state | { state . optional ( | state | { self :: postfix_operator ( state ) . and_then ( | state | { state . repeat ( | state | { state . sequence ( | state | { super :: hidden :: skip ( state ) . and_then ( | state | { self :: postfix_operator ( state ) } ) } ) } ) } ) } ) } ) } ) } ) } ) } # [ inline ] # [ allow ( non_snake_case , unused_variables ) ] pub fn node ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { state . sequence ( | state | { self :: opening_paren ( state ) . and_then ( | state | { super :: hidden :: skip ( state ) } ) . and_then ( | state | { self :: expression ( state ) } ) . and_then ( | state | { super :: hidden :: skip ( state ) } ) . and_then ( | state | { self :: closing_paren ( state ) } ) } ) . or_else ( | state | { self :: terminal ( state ) } ) } # [ inline ] # [ allow ( non_snake_case , unused_variables ) ] pub fn terminal ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { self :: _push ( state ) . or_else ( | state | { self :: peek_slice ( state ) } ) . or_else ( | state | { self :: identifier ( state ) } ) . or_else ( | state | { self :: string ( state ) } ) . or_else ( | state | { self :: insensitive_string ( state ) } ) . or_else ( | state | { self :: range ( state ) } ) } # [ inline ] # [ allow ( non_snake_case , unused_variables ) ] pub fn prefix_operator ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { self :: positive_predicate_operator ( state ) . or_else ( | state | { self :: negative_predicate_operator ( state ) } ) } # [ inline ] # [ allow ( non_snake_case , unused_variables ) ] pub fn infix_operator ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { self :: sequence_operator ( state ) . or_else ( | state | { self :: choice_operator ( state ) } ) } # [ inline ] # [ allow ( non_snake_case , unused_variables ) ] pub fn postfix_operator ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { self :: optional_operator ( state ) . or_else ( | state | { self :: repeat_operator ( state ) } ) . or_else ( | state | { self :: repeat_once_operator ( state ) } ) . or_else ( | state | { self :: repeat_exact ( state ) } ) . or_else ( | state | { self :: repeat_min ( state ) } ) . or_else ( | state | { self :: repeat_max ( state ) } ) . or_else ( | state | { self :: repeat_min_max ( state ) } ) } # [ inline ] # [ allow ( non_snake_case , unused_variables ) ] pub fn positive_predicate_operator ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { state . rule ( Rule :: positive_predicate_operator , | state | { state . match_string ( "&" ) } ) } # [ inline ] # [ allow ( non_snake_case , unused_variables ) ] pub fn negative_predicate_operator ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { state . rule ( Rule :: negative_predicate_operator , | state | { state . match_string ( "!" ) } ) } # [ inline ] # [ allow ( non_snake_case , unused_variables ) ] pub fn sequence_operator ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { state . rule ( Rule :: sequence_operator , | state | { state . match_string ( "~" ) } ) } # [ inline ] # [ allow ( non_snake_case , unused_variables ) ] pub fn choice_operator ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { state . rule ( Rule :: choice_operator , | state | { state . match_string ( "|" ) } ) } # [ inline ] # [ allow ( non_snake_case , unused_variables ) ] pub fn optional_operator ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { state . rule ( Rule :: optional_operator , | state | { state . match_string ( "?" ) } ) } # [ inline ] # [ allow ( non_snake_case , unused_variables ) ] pub fn repeat_operator ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { state . rule ( Rule :: repeat_operator , | state | { state . match_string ( "*" ) } ) } # [ inline ] # [ allow ( non_snake_case , unused_variables ) ] pub fn repeat_once_operator ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { state . rule ( Rule :: repeat_once_operator , | state | { state . match_string ( "+" ) } ) } # [ inline ] # [ allow ( non_snake_case , unused_variables ) ] pub fn repeat_exact ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { state . rule ( Rule :: repeat_exact , | state | { state . sequence ( | state | { self :: opening_brace ( state ) . and_then ( | state | { super :: hidden :: skip ( state ) } ) . and_then ( | state | { self :: number ( state ) } ) . and_then ( | state | { super :: hidden :: skip ( state ) } ) . and_then ( | state | { self :: closing_brace ( state ) } ) } ) } ) } # [ inline ] # [ allow ( non_snake_case , unused_variables ) ] pub fn repeat_min ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { state . rule ( Rule :: repeat_min , | state | { state . sequence ( | state | { self :: opening_brace ( state ) . and_then ( | state | { super :: hidden :: skip ( state ) } ) . and_then ( | state | { self :: number ( state ) } ) . and_then ( | state | { super :: hidden :: skip ( state ) } ) . and_then ( | state | { self :: comma ( state ) } ) . and_then ( | state | { super :: hidden :: skip ( state ) } ) . and_then ( | state | { self :: closing_brace ( state ) } ) } ) } ) } # [ inline ] # [ allow ( non_snake_case , unused_variables ) ] pub fn repeat_max ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { state . rule ( Rule :: repeat_max , | state | { state . sequence ( | state | { self :: opening_brace ( state ) . and_then ( | state | { super :: hidden :: skip ( state ) } ) . and_then ( | state | { self :: comma ( state ) } ) . and_then ( | state | { super :: hidden :: skip ( state ) } ) . and_then ( | state | { self :: number ( state ) } ) . and_then ( | state | { super :: hidden :: skip ( state ) } ) . and_then ( | state | { self :: closing_brace ( state ) } ) } ) } ) } # [ inline ] # [ allow ( non_snake_case , unused_variables ) ] pub fn repeat_min_max ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { state . rule ( Rule :: repeat_min_max , | state | { state . sequence ( | state | { self :: opening_brace ( state ) . and_then ( | state | { super :: hidden :: skip ( state ) } ) . and_then ( | state | { self :: number ( state ) } ) . and_then ( | state | { super :: hidden :: skip ( state ) } ) . and_then ( | state | { self :: comma ( state ) } ) . and_then ( | state | { super :: hidden :: skip ( state ) } ) . and_then ( | state | { self :: number ( state ) } ) . and_then ( | state | { super :: hidden :: skip ( state ) } ) . and_then ( | state | { self :: closing_brace ( state ) } ) } ) } ) } # [ inline ] # [ allow ( non_snake_case , unused_variables ) ] pub fn number ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { state . rule ( Rule :: number , | state | { state . atomic ( :: pest :: Atomicity :: Atomic , | state | { state . sequence ( | state | { state . match_range ( '0' .. '9' ) . and_then ( | state | { state . repeat ( | state | { state . match_range ( '0' .. '9' ) } ) } ) } ) } ) } ) } # [ inline ] # [ allow ( non_snake_case , unused_variables ) ] pub fn integer ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { state . rule ( Rule :: integer , | state | { state . atomic ( :: pest :: Atomicity :: Atomic , | state | { self :: number ( state ) . or_else ( | state | { state . sequence ( | state | { state . match_string ( "-" ) . and_then ( | state | { state . repeat ( | state | { state . match_string ( "0" ) } ) } ) . and_then ( | state | { state . match_range ( '1' .. '9' ) } ) . and_then ( | state | { state . optional ( | state | { self :: number ( state ) } ) } ) } ) } ) } ) } ) } # [ inline ] # [ allow ( non_snake_case , unused_variables ) ] pub fn comma ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { state . rule ( Rule :: comma , | state | { state . match_string ( "," ) } ) } # [ inline ] # [ allow ( non_snake_case , unused_variables ) ] pub fn _push ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { state . rule ( Rule :: _push , | state | { state . sequence ( | state | { state . match_string ( "PUSH" ) . and_then ( | state | { super :: hidden :: skip ( state ) } ) . and_then ( | state | { self :: opening_paren ( state ) } ) . and_then ( | state | { super :: hidden :: skip ( state ) } ) . and_then ( | state | { self :: expression ( state ) } ) . and_then ( | state | { super :: hidden :: skip ( state ) } ) . and_then ( | state | { self :: closing_paren ( state ) } ) } ) } ) } # [ inline ] # [ allow ( non_snake_case , unused_variables ) ] pub fn peek_slice ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { state . rule ( Rule :: peek_slice , | state | { state . sequence ( | state | { state . match_string ( "PEEK" ) . and_then ( | state | { super :: hidden :: skip ( state ) } ) . and_then ( | state | { self :: opening_brack ( state ) } ) . and_then ( | state | { super :: hidden :: skip ( state ) } ) . and_then ( | state | { state . optional ( | state | { self :: integer ( state ) } ) } ) . and_then ( | state | { super :: hidden :: skip ( state ) } ) . and_then ( | state | { self :: range_operator ( state ) } ) . and_then ( | state | { super :: hidden :: skip ( state ) } ) . and_then ( | state | { state . optional ( | state | { self :: integer ( state ) } ) } ) . and_then ( | state | { super :: hidden :: skip ( state ) } ) . and_then ( | state | { self :: closing_brack ( state ) } ) } ) } ) } # [ inline ] # [ allow ( non_snake_case , unused_variables ) ] pub fn identifier ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { state . rule ( Rule :: identifier , | state | { state . atomic ( :: pest :: Atomicity :: Atomic , | state | { state . sequence ( | state | { state . lookahead ( false , | state | { state . match_string ( "PUSH" ) } ) . and_then ( | state | { state . match_string ( "_" ) . or_else ( | state | { self :: alpha ( state ) } ) } ) . and_then ( | state | { state . repeat ( | state | { state . match_string ( "_" ) . or_else ( | state | { self :: alpha_num ( state ) } ) } ) } ) } ) } ) } ) } # [ inline ] # [ allow ( non_snake_case , unused_variables ) ] pub fn alpha ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { state . match_range ( 'a' .. 'z' ) . or_else ( | state | { state . match_range ( 'A' .. 'Z' ) } ) } # [ inline ] # [ allow ( non_snake_case , unused_variables ) ] pub fn alpha_num ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { self :: alpha ( state ) . or_else ( | state | { state . match_range ( '0' .. '9' ) } ) } # [ inline ] # [ allow ( non_snake_case , unused_variables ) ] pub fn string ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { state . atomic ( :: pest :: Atomicity :: CompoundAtomic , | state | { state . rule ( Rule :: string , | state | { state . sequence ( | state | { self :: quote ( state ) . and_then ( | state | { self :: inner_str ( state ) } ) . and_then ( | state | { self :: quote ( state ) } ) } ) } ) } ) } # [ inline ] # [ allow ( non_snake_case , unused_variables ) ] pub fn insensitive_string ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { state . rule ( Rule :: insensitive_string , | state | { state . sequence ( | state | { state . match_string ( "^" ) . and_then ( | state | { super :: hidden :: skip ( state ) } ) . and_then ( | state | { self :: string ( state ) } ) } ) } ) } # [ inline ] # [ allow ( non_snake_case , unused_variables ) ] pub fn range ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { state . rule ( Rule :: range , | state | { state . sequence ( | state | { self :: character ( state ) . and_then ( | state | { super :: hidden :: skip ( state ) } ) . and_then ( | state | { self :: range_operator ( state ) } ) . and_then ( | state | { super :: hidden :: skip ( state ) } ) . and_then ( | state | { self :: character ( state ) } ) } ) } ) } # [ inline ] # [ allow ( non_snake_case , unused_variables ) ] pub fn character ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { state . atomic ( :: pest :: Atomicity :: CompoundAtomic , | state | { state . rule ( Rule :: character , | state | { state . sequence ( | state | { self :: single_quote ( state ) . and_then ( | state | { self :: inner_chr ( state ) } ) . and_then ( | state | { self :: single_quote ( state ) } ) } ) } ) } ) } # [ inline ] # [ allow ( non_snake_case , unused_variables ) ] pub fn inner_str ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { state . rule ( Rule :: inner_str , | state | { state . atomic ( :: pest :: Atomicity :: Atomic , | state | { state . sequence ( | state | { let strings = [ "\"" , "\\" ] ; state . skip_until ( & strings ) . and_then ( | state | { state . optional ( | state | { state . sequence ( | state | { self :: escape ( state ) . and_then ( | state | { self :: inner_str ( state ) } ) } ) } ) } ) } ) } ) } ) } # [ inline ] # [ allow ( non_snake_case , unused_variables ) ] pub fn inner_chr ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { state . rule ( Rule :: inner_chr , | state | { state . atomic ( :: pest :: Atomicity :: Atomic , | state | { self :: escape ( state ) . or_else ( | state | { self :: ANY ( state ) } ) } ) } ) } # [ inline ] # [ allow ( non_snake_case , unused_variables ) ] pub fn escape ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { state . rule ( Rule :: escape , | state | { state . atomic ( :: pest :: Atomicity :: Atomic , | state | { state . sequence ( | state | { state . match_string ( "\\" ) . and_then ( | state | { state . match_string ( "\"" ) . or_else ( | state | { state . match_string ( "\\" ) } ) . or_else ( | state | { state . match_string ( "r" ) } ) . or_else ( | state | { state . match_string ( "n" ) } ) . or_else ( | state | { state . match_string ( "t" ) } ) . or_else ( | state | { state . match_string ( "0" ) } ) . or_else ( | state | { state . match_string ( "'" ) } ) . or_else ( | state | { self :: code ( state ) } ) . or_else ( | state | { self :: unicode ( state ) } ) } ) } ) } ) } ) } # [ inline ] # [ allow ( non_snake_case , unused_variables ) ] pub fn code ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { state . rule ( Rule :: code , | state | { state . atomic ( :: pest :: Atomicity :: Atomic , | state | { state . sequence ( | state | { state . match_string ( "x" ) . and_then ( | state | { self :: hex_digit ( state ) } ) . and_then ( | state | { self :: hex_digit ( state ) } ) } ) } ) } ) } # [ inline ] # [ allow ( non_snake_case , unused_variables ) ] pub fn unicode ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { state . rule ( Rule :: unicode , | state | { state . atomic ( :: pest :: Atomicity :: Atomic , | state | { state . sequence ( | state | { state . match_string ( "u" ) . and_then ( | state | { self :: opening_brace ( state ) } ) . and_then ( | state | { state . sequence ( | state | { self :: hex_digit ( state ) . and_then ( | state | { self :: hex_digit ( state ) } ) . and_then ( | state | { state . optional ( | state | { self :: hex_digit ( state ) } ) } ) . and_then ( | state | { state . optional ( | state | { self :: hex_digit ( state ) } ) } ) . and_then ( | state | { state . optional ( | state | { self :: hex_digit ( state ) } ) } ) . and_then ( | state | { state . optional ( | state | { self :: hex_digit ( state ) } ) } ) } ) } ) . and_then ( | state | { self :: closing_brace ( state ) } ) } ) } ) } ) } # [ inline ] # [ allow ( non_snake_case , unused_variables ) ] pub fn hex_digit ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { state . rule ( Rule :: hex_digit , | state | { state . atomic ( :: pest :: Atomicity :: Atomic , | state | { state . match_range ( '0' .. '9' ) . or_else ( | state | { state . match_range ( 'a' .. 'f' ) } ) . or_else ( | state | { state . match_range ( 'A' .. 'F' ) } ) } ) } ) } # [ inline ] # [ allow ( non_snake_case , unused_variables ) ] pub fn quote ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { state . rule ( Rule :: quote , | state | { state . match_string ( "\"" ) } ) } # [ inline ] # [ allow ( non_snake_case , unused_variables ) ] pub fn single_quote ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { state . rule ( Rule :: single_quote , | state | { state . match_string ( "'" ) } ) } # [ inline ] # [ allow ( non_snake_case , unused_variables ) ] pub fn range_operator ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { state . rule ( Rule :: range_operator , | state | { state . match_string ( ".." ) } ) } # [ inline ] # [ allow ( non_snake_case , unused_variables ) ] pub fn newline ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { state . match_string ( "\n" ) . or_else ( | state | { state . match_string ( "\r\n" ) } ) } # [ inline ] # [ allow ( non_snake_case , unused_variables ) ] pub fn WHITESPACE ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { state . atomic ( :: pest :: Atomicity :: Atomic , | state | { state . match_string ( " " ) . or_else ( | state | { state . match_string ( "\t" ) } ) . or_else ( | state | { self :: newline ( state ) } ) } ) } # [ inline ] # [ allow ( non_snake_case , unused_variables ) ] pub fn block_comment ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { state . sequence ( | state | { state . match_string ( "/*" ) . and_then ( | state | { super :: hidden :: skip ( state ) } ) . and_then ( | state | { state . sequence ( | state | { state . optional ( | state | { self :: block_comment ( state ) . or_else ( | state | { state . sequence ( | state | { state . lookahead ( false , | state | { state . match_string ( "*/" ) } ) . and_then ( | state | { super :: hidden :: skip ( state ) } ) . and_then ( | state | { self :: ANY ( state ) } ) } ) } ) . and_then ( | state | { state . repeat ( | state | { state . sequence ( | state | { super :: hidden :: skip ( state ) . and_then ( | state | { self :: block_comment ( state ) . or_else ( | state | { state . sequence ( | state | { state . lookahead ( false , | state | { state . match_string ( "*/" ) } ) . and_then ( | state | { super :: hidden :: skip ( state ) } ) . and_then ( | state | { self :: ANY ( state ) } ) } ) } ) } ) } ) } ) } ) } ) } ) } ) . and_then ( | state | { super :: hidden :: skip ( state ) } ) . and_then ( | state | { state . match_string ( "*/" ) } ) } ) } # [ inline ] # [ allow ( non_snake_case , unused_variables ) ] pub fn COMMENT ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { state . atomic ( :: pest :: Atomicity :: Atomic , | state | { self :: block_comment ( state ) . or_else ( | state | { state . sequence ( | state | { state . match_string ( "//" ) . and_then ( | state | { state . repeat ( | state | { state . sequence ( | state | { state . lookahead ( false , | state | { self :: newline ( state ) } ) . and_then ( | state | { self :: ANY ( state ) } ) } ) } ) } ) } ) } ) } ) } # [ inline ] # [ allow ( dead_code , non_snake_case , unused_variables ) ] pub fn SOI ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { state . start_of_input ( ) } # [ inline ] # [ allow ( dead_code , non_snake_case , unused_variables ) ] pub fn ANY ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { state . skip ( 1 ) } # [ inline ] # [ allow ( dead_code , non_snake_case , unused_variables ) ] pub fn EOI ( state : Box < :: pest :: ParserState < Rule >> ) -> :: pest :: ParseResult < Box < :: pest :: ParserState < Rule >> > { state . rule ( Rule :: EOI , | state | state . end_of_input ( ) ) } } pub use self :: visible :: * ; } :: pest :: state ( input , | state | { match rule { Rule :: grammar_rules => rules :: grammar_rules ( state ) , Rule :: grammar_rule => rules :: grammar_rule ( state ) , Rule :: assignment_operator => rules :: assignment_operator ( state ) , Rule :: opening_brace => rules :: opening_brace ( state ) , Rule :: closing_brace => rules :: closing_brace ( state ) , Rule :: opening_paren => rules :: opening_paren ( state ) , Rule :: closing_paren => rules :: closing_paren ( state ) , Rule :: opening_brack => rules :: opening_brack ( state ) , Rule :: closing_brack => rules :: closing_brack ( state ) , Rule :: modifier => rules :: modifier ( state ) , Rule :: silent_modifier => rules :: silent_modifier ( state ) , Rule :: atomic_modifier => rules :: atomic_modifier ( state ) , Rule :: compound_atomic_modifier => rules :: compound_atomic_modifier ( state ) , Rule :: non_atomic_modifier => rules :: non_atomic_modifier ( state ) , Rule :: expression => rules :: expression ( state ) , Rule :: term => rules :: term ( state ) , Rule :: node => rules :: node ( state ) , Rule :: terminal => rules :: terminal ( state ) , Rule :: prefix_operator => rules :: prefix_operator ( state ) , Rule :: infix_operator => rules :: infix_operator ( state ) , Rule :: postfix_operator => rules :: postfix_operator ( state ) , Rule :: positive_predicate_operator => rules :: positive_predicate_operator ( state ) , Rule :: negative_predicate_operator => rules :: negative_predicate_operator ( state ) , Rule :: sequence_operator => rules :: sequence_operator ( state ) , Rule :: choice_operator => rules :: choice_operator ( state ) , Rule :: optional_operator => rules :: optional_operator ( state ) , Rule :: repeat_operator => rules :: repeat_operator ( state ) , Rule :: repeat_once_operator => rules :: repeat_once_operator ( state ) , Rule :: repeat_exact => rules :: repeat_exact ( state ) , Rule :: repeat_min => rules :: repeat_min ( state ) , Rule :: repeat_max => rules :: repeat_max ( state ) , Rule :: repeat_min_max => rules :: repeat_min_max ( state ) , Rule :: number => rules :: number ( state ) , Rule :: integer => rules :: integer ( state ) , Rule :: comma => rules :: comma ( state ) , Rule :: _push => rules :: _push ( state ) , Rule :: peek_slice => rules :: peek_slice ( state ) , Rule :: identifier => rules :: identifier ( state ) , Rule :: alpha => rules :: alpha ( state ) , Rule :: alpha_num => rules :: alpha_num ( state ) , Rule :: string => rules :: string ( state ) , Rule :: insensitive_string => rules :: insensitive_string ( state ) , Rule :: range => rules :: range ( state ) , Rule :: character => rules :: character ( state ) , Rule :: inner_str => rules :: inner_str ( state ) , Rule :: inner_chr => rules :: inner_chr ( state ) , Rule :: escape => rules :: escape ( state ) , Rule :: code => rules :: code ( state ) , Rule :: unicode => rules :: unicode ( state ) , Rule :: hex_digit => rules :: hex_digit ( state ) , Rule :: quote => rules :: quote ( state ) , Rule :: single_quote => rules :: single_quote ( state ) , Rule :: range_operator => rules :: range_operator ( state ) , Rule :: newline => rules :: newline ( state ) , Rule :: WHITESPACE => rules :: WHITESPACE ( state ) , Rule :: block_comment => rules :: block_comment ( state ) , Rule :: COMMENT => rules :: COMMENT ( state ) , Rule :: EOI => rules :: EOI ( state ) } } ) } }
diff --git a/src/lib.rs b/src/lib.rs
new file mode 100644
index 0000000..28f33b0
--- /dev/null
+++ b/src/lib.rs
@@ -0,0 +1,133 @@
+// pest. The Elegant Parser
+// Copyright (c) 2018 Dragoș Tiselice
+//
+// Licensed under the Apache License, Version 2.0
+// <LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0> or the MIT
+// license <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. All files in the project carrying such notice may not be copied,
+// modified, or distributed except according to those terms.
+
+#![allow(clippy::range_plus_one)]
+
+#[cfg(test)]
+#[macro_use]
+extern crate pest;
+#[cfg(not(test))]
+extern crate pest;
+
+use std::fmt::Display;
+
+pub mod ast;
+pub mod optimizer;
+pub mod parser;
+pub mod validator;
+
+pub fn unwrap_or_report<T, E>(result: Result<T, E>) -> T
+where
+    E: IntoIterator,
+    E::Item: Display,
+{
+    result.unwrap_or_else(|e| {
+        panic!(
+            "grammar error\n\n".to_owned()
+                + &e.into_iter()
+                    .map(|error| format!("{}", error))
+                    .collect::<Vec<_>>()
+                    .join("\n\n")
+        )
+    })
+}
+
+#[doc(hidden)]
+pub static UNICODE_PROPERTY_NAMES: &[&str] = &[
+    /* BINARY */ "ALPHABETIC",
+    "BIDI_CONTROL",
+    "CASE_IGNORABLE",
+    "CASED",
+    "CHANGES_WHEN_CASEFOLDED",
+    "CHANGES_WHEN_CASEMAPPED",
+    "CHANGES_WHEN_LOWERCASED",
+    "CHANGES_WHEN_TITLECASED",
+    "CHANGES_WHEN_UPPERCASED",
+    "DASH",
+    "DEFAULT_IGNORABLE_CODE_POINT",
+    "DEPRECATED",
+    "DIACRITIC",
+    "EXTENDER",
+    "GRAPHEME_BASE",
+    "GRAPHEME_EXTEND",
+    "GRAPHEME_LINK",
+    "HEX_DIGIT",
+    "HYPHEN",
+    "IDS_BINARY_OPERATOR",
+    "IDS_TRINARY_OPERATOR",
+    "ID_CONTINUE",
+    "ID_START",
+    "IDEOGRAPHIC",
+    "JOIN_CONTROL",
+    "LOGICAL_ORDER_EXCEPTION",
+    "LOWERCASE",
+    "MATH",
+    "NONCHARACTER_CODE_POINT",
+    "OTHER_ALPHABETIC",
+    "OTHER_DEFAULT_IGNORABLE_CODE_POINT",
+    "OTHER_GRAPHEME_EXTEND",
+    "OTHER_ID_CONTINUE",
+    "OTHER_ID_START",
+    "OTHER_LOWERCASE",
+    "OTHER_MATH",
+    "OTHER_UPPERCASE",
+    "PATTERN_SYNTAX",
+    "PATTERN_WHITE_SPACE",
+    "PREPENDED_CONCATENATION_MARK",
+    "QUOTATION_MARK",
+    "RADICAL",
+    "REGIONAL_INDICATOR",
+    "SENTENCE_TERMINAL",
+    "SOFT_DOTTED",
+    "TERMINAL_PUNCTUATION",
+    "UNIFIED_IDEOGRAPH",
+    "UPPERCASE",
+    "VARIATION_SELECTOR",
+    "WHITE_SPACE",
+    "XID_CONTINUE",
+    "XID_START",
+    /* CATEGORY */ "CASED_LETTER",
+    "CLOSE_PUNCTUATION",
+    "CONNECTOR_PUNCTUATION",
+    "CONTROL",
+    "CURRENCY_SYMBOL",
+    "DASH_PUNCTUATION",
+    "DECIMAL_NUMBER",
+    "ENCLOSING_MARK",
+    "FINAL_PUNCTUATION",
+    "FORMAT",
+    "INITIAL_PUNCTUATION",
+    "LETTER",
+    "LETTER_NUMBER",
+    "LINE_SEPARATOR",
+    "LOWERCASE_LETTER",
+    "MARK",
+    "MATH_SYMBOL",
+    "MODIFIER_LETTER",
+    "MODIFIER_SYMBOL",
+    "NONSPACING_MARK",
+    "NUMBER",
+    "OPEN_PUNCTUATION",
+    "OTHER",
+    "OTHER_LETTER",
+    "OTHER_NUMBER",
+    "OTHER_PUNCTUATION",
+    "OTHER_SYMBOL",
+    "PARAGRAPH_SEPARATOR",
+    "PRIVATE_USE",
+    "PUNCTUATION",
+    "SEPARATOR",
+    "SPACE_SEPARATOR",
+    "SPACING_MARK",
+    "SURROGATE",
+    "SYMBOL",
+    "TITLECASE_LETTER",
+    "UNASSIGNED",
+    "UPPERCASE_LETTER",
+];
diff --git a/src/optimizer/concatenator.rs b/src/optimizer/concatenator.rs
new file mode 100644
index 0000000..e0aab7b
--- /dev/null
+++ b/src/optimizer/concatenator.rs
@@ -0,0 +1,34 @@
+// pest. The Elegant Parser
+// Copyright (c) 2018 Dragoș Tiselice
+//
+// Licensed under the Apache License, Version 2.0
+// <LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0> or the MIT
+// license <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. All files in the project carrying such notice may not be copied,
+// modified, or distributed except according to those terms.
+
+use ast::*;
+
+pub fn concatenate(rule: Rule) -> Rule {
+    match rule {
+        Rule { name, ty, expr } => Rule {
+            name,
+            ty,
+            expr: expr.map_bottom_up(|expr| {
+                if ty == RuleType::Atomic {
+                    // TODO: Use box syntax when it gets stabilized.
+                    match expr {
+                        Expr::Seq(lhs, rhs) => match (*lhs, *rhs) {
+                            (Expr::Str(lhs), Expr::Str(rhs)) => Expr::Str(lhs + &rhs),
+                            (Expr::Insens(lhs), Expr::Insens(rhs)) => Expr::Insens(lhs + &rhs),
+                            (lhs, rhs) => Expr::Seq(Box::new(lhs), Box::new(rhs)),
+                        },
+                        expr => expr,
+                    }
+                } else {
+                    expr
+                }
+            }),
+        },
+    }
+}
diff --git a/src/optimizer/factorizer.rs b/src/optimizer/factorizer.rs
new file mode 100644
index 0000000..236289e
--- /dev/null
+++ b/src/optimizer/factorizer.rs
@@ -0,0 +1,38 @@
+// pest. The Elegant Parser
+// Copyright (c) 2018 Dragoș Tiselice
+//
+// Licensed under the Apache License, Version 2.0
+// <LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0> or the MIT
+// license <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. All files in the project carrying such notice may not be copied,
+// modified, or distributed except according to those terms.
+
+use ast::*;
+
+pub fn factor(rule: Rule) -> Rule {
+    match rule {
+        Rule { name, ty, expr } => Rule {
+            name,
+            ty,
+            expr: expr.map_top_down(|expr| {
+                // TODO: Use box syntax when it gets stabilized.
+                match expr {
+                    Expr::Choice(lhs, rhs) => match (*lhs, *rhs) {
+                        (Expr::Seq(l1, r1), Expr::Seq(l2, r2)) => {
+                            if l1 == l2 {
+                                Expr::Seq(l1, Box::new(Expr::Choice(r1, r2)))
+                            } else {
+                                Expr::Choice(
+                                    Box::new(Expr::Seq(l1, r1)),
+                                    Box::new(Expr::Seq(l2, r2)),
+                                )
+                            }
+                        }
+                        (lhs, rhs) => Expr::Choice(Box::new(lhs), Box::new(rhs)),
+                    },
+                    expr => expr,
+                }
+            }),
+        },
+    }
+}
diff --git a/src/optimizer/mod.rs b/src/optimizer/mod.rs
new file mode 100644
index 0000000..7013c43
--- /dev/null
+++ b/src/optimizer/mod.rs
@@ -0,0 +1,510 @@
+// pest. The Elegant Parser
+// Copyright (c) 2018 Dragoș Tiselice
+//
+// Licensed under the Apache License, Version 2.0
+// <LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0> or the MIT
+// license <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. All files in the project carrying such notice may not be copied,
+// modified, or distributed except according to those terms.
+
+use ast::*;
+use std::collections::HashMap;
+
+#[cfg(test)]
+macro_rules! box_tree {
+    ( $node:ident( $(                      $child:ident( $($args:tt)* )     ),+ ) ) => (
+      $node      ( $( Box::new( box_tree!( $child      ( $($args   )* ) ) ) ),+ )
+    );
+    ($expr:expr) => ($expr);
+}
+
+mod concatenator;
+mod factorizer;
+mod restorer;
+mod rotater;
+mod skipper;
+mod unroller;
+
+pub fn optimize(rules: Vec<Rule>) -> Vec<OptimizedRule> {
+    let optimized: Vec<OptimizedRule> = rules
+        .into_iter()
+        .map(rotater::rotate)
+        .map(skipper::skip)
+        .map(unroller::unroll)
+        .map(concatenator::concatenate)
+        .map(factorizer::factor)
+        .map(rule_to_optimized_rule)
+        .collect();
+
+    let rules = to_hash_map(&optimized);
+    optimized
+        .into_iter()
+        .map(|rule| restorer::restore_on_err(rule, &rules))
+        .collect()
+}
+
+fn rule_to_optimized_rule(rule: Rule) -> OptimizedRule {
+    fn to_optimized(expr: Expr) -> OptimizedExpr {
+        match expr {
+            Expr::Str(string) => OptimizedExpr::Str(string),
+            Expr::Insens(string) => OptimizedExpr::Insens(string),
+            Expr::Range(start, end) => OptimizedExpr::Range(start, end),
+            Expr::Ident(ident) => OptimizedExpr::Ident(ident),
+            Expr::PeekSlice(start, end) => OptimizedExpr::PeekSlice(start, end),
+            Expr::PosPred(expr) => OptimizedExpr::PosPred(Box::new(to_optimized(*expr))),
+            Expr::NegPred(expr) => OptimizedExpr::NegPred(Box::new(to_optimized(*expr))),
+            Expr::Seq(lhs, rhs) => {
+                OptimizedExpr::Seq(Box::new(to_optimized(*lhs)), Box::new(to_optimized(*rhs)))
+            }
+            Expr::Choice(lhs, rhs) => {
+                OptimizedExpr::Choice(Box::new(to_optimized(*lhs)), Box::new(to_optimized(*rhs)))
+            }
+            Expr::Opt(expr) => OptimizedExpr::Opt(Box::new(to_optimized(*expr))),
+            Expr::Rep(expr) => OptimizedExpr::Rep(Box::new(to_optimized(*expr))),
+            Expr::Skip(strings) => OptimizedExpr::Skip(strings),
+            Expr::Push(expr) => OptimizedExpr::Push(Box::new(to_optimized(*expr))),
+            Expr::RepOnce(_)
+            | Expr::RepExact(..)
+            | Expr::RepMin(..)
+            | Expr::RepMax(..)
+            | Expr::RepMinMax(..) => unreachable!("No valid transformation to OptimizedRule"),
+        }
+    }
+
+    OptimizedRule {
+        name: rule.name,
+        ty: rule.ty,
+        expr: to_optimized(rule.expr),
+    }
+}
+
+fn to_hash_map(rules: &[OptimizedRule]) -> HashMap<String, OptimizedExpr> {
+    rules
+        .iter()
+        .map(|r| (r.name.clone(), r.expr.clone()))
+        .collect()
+}
+
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub struct OptimizedRule {
+    pub name: String,
+    pub ty: RuleType,
+    pub expr: OptimizedExpr,
+}
+
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub enum OptimizedExpr {
+    Str(String),
+    Insens(String),
+    Range(String, String),
+    Ident(String),
+    PeekSlice(i32, Option<i32>),
+    PosPred(Box<OptimizedExpr>),
+    NegPred(Box<OptimizedExpr>),
+    Seq(Box<OptimizedExpr>, Box<OptimizedExpr>),
+    Choice(Box<OptimizedExpr>, Box<OptimizedExpr>),
+    Opt(Box<OptimizedExpr>),
+    Rep(Box<OptimizedExpr>),
+    Skip(Vec<String>),
+    Push(Box<OptimizedExpr>),
+    RestoreOnErr(Box<OptimizedExpr>),
+}
+
+impl OptimizedExpr {
+    pub fn iter_top_down(&self) -> OptimizedExprTopDownIterator {
+        OptimizedExprTopDownIterator::new(self)
+    }
+
+    pub fn map_top_down<F>(self, mut f: F) -> OptimizedExpr
+    where
+        F: FnMut(OptimizedExpr) -> OptimizedExpr,
+    {
+        fn map_internal<F>(expr: OptimizedExpr, f: &mut F) -> OptimizedExpr
+        where
+            F: FnMut(OptimizedExpr) -> OptimizedExpr,
+        {
+            let expr = f(expr);
+
+            match expr {
+                // TODO: Use box syntax when it gets stabilized.
+                OptimizedExpr::PosPred(expr) => {
+                    let mapped = Box::new(map_internal(*expr, f));
+                    OptimizedExpr::PosPred(mapped)
+                }
+                OptimizedExpr::NegPred(expr) => {
+                    let mapped = Box::new(map_internal(*expr, f));
+                    OptimizedExpr::NegPred(mapped)
+                }
+                OptimizedExpr::Seq(lhs, rhs) => {
+                    let mapped_lhs = Box::new(map_internal(*lhs, f));
+                    let mapped_rhs = Box::new(map_internal(*rhs, f));
+                    OptimizedExpr::Seq(mapped_lhs, mapped_rhs)
+                }
+                OptimizedExpr::Choice(lhs, rhs) => {
+                    let mapped_lhs = Box::new(map_internal(*lhs, f));
+                    let mapped_rhs = Box::new(map_internal(*rhs, f));
+                    OptimizedExpr::Choice(mapped_lhs, mapped_rhs)
+                }
+                OptimizedExpr::Rep(expr) => {
+                    let mapped = Box::new(map_internal(*expr, f));
+                    OptimizedExpr::Rep(mapped)
+                }
+                OptimizedExpr::Opt(expr) => {
+                    let mapped = Box::new(map_internal(*expr, f));
+                    OptimizedExpr::Opt(mapped)
+                }
+                OptimizedExpr::Push(expr) => {
+                    let mapped = Box::new(map_internal(*expr, f));
+                    OptimizedExpr::Push(mapped)
+                }
+                expr => expr,
+            }
+        }
+
+        map_internal(self, &mut f)
+    }
+
+    pub fn map_bottom_up<F>(self, mut f: F) -> OptimizedExpr
+    where
+        F: FnMut(OptimizedExpr) -> OptimizedExpr,
+    {
+        fn map_internal<F>(expr: OptimizedExpr, f: &mut F) -> OptimizedExpr
+        where
+            F: FnMut(OptimizedExpr) -> OptimizedExpr,
+        {
+            let mapped = match expr {
+                OptimizedExpr::PosPred(expr) => {
+                    // TODO: Use box syntax when it gets stabilized.
+                    let mapped = Box::new(map_internal(*expr, f));
+                    OptimizedExpr::PosPred(mapped)
+                }
+                OptimizedExpr::NegPred(expr) => {
+                    let mapped = Box::new(map_internal(*expr, f));
+                    OptimizedExpr::NegPred(mapped)
+                }
+                OptimizedExpr::Seq(lhs, rhs) => {
+                    let mapped_lhs = Box::new(map_internal(*lhs, f));
+                    let mapped_rhs = Box::new(map_internal(*rhs, f));
+                    OptimizedExpr::Seq(mapped_lhs, mapped_rhs)
+                }
+                OptimizedExpr::Choice(lhs, rhs) => {
+                    let mapped_lhs = Box::new(map_internal(*lhs, f));
+                    let mapped_rhs = Box::new(map_internal(*rhs, f));
+                    OptimizedExpr::Choice(mapped_lhs, mapped_rhs)
+                }
+                OptimizedExpr::Rep(expr) => {
+                    let mapped = Box::new(map_internal(*expr, f));
+                    OptimizedExpr::Rep(mapped)
+                }
+                OptimizedExpr::Opt(expr) => {
+                    let mapped = Box::new(map_internal(*expr, f));
+                    OptimizedExpr::Opt(mapped)
+                }
+                OptimizedExpr::Push(expr) => {
+                    let mapped = Box::new(map_internal(*expr, f));
+                    OptimizedExpr::Push(mapped)
+                }
+                expr => expr,
+            };
+
+            f(mapped)
+        }
+
+        map_internal(self, &mut f)
+    }
+}
+
+pub struct OptimizedExprTopDownIterator {
+    current: Option<OptimizedExpr>,
+    next: Option<OptimizedExpr>,
+    right_branches: Vec<OptimizedExpr>,
+}
+
+impl OptimizedExprTopDownIterator {
+    pub fn new(expr: &OptimizedExpr) -> Self {
+        let mut iter = OptimizedExprTopDownIterator {
+            current: None,
+            next: None,
+            right_branches: vec![],
+        };
+        iter.iterate_expr(expr.clone());
+        iter
+    }
+
+    fn iterate_expr(&mut self, expr: OptimizedExpr) {
+        self.current = Some(expr.clone());
+        match expr {
+            OptimizedExpr::Seq(lhs, rhs) => {
+                self.right_branches.push(*rhs);
+                self.next = Some(*lhs);
+            }
+            OptimizedExpr::Choice(lhs, rhs) => {
+                self.right_branches.push(*rhs);
+                self.next = Some(*lhs);
+            }
+            OptimizedExpr::PosPred(expr)
+            | OptimizedExpr::NegPred(expr)
+            | OptimizedExpr::Rep(expr)
+            | OptimizedExpr::Opt(expr)
+            | OptimizedExpr::Push(expr) => {
+                self.next = Some(*expr);
+            }
+            _ => {
+                self.next = None;
+            }
+        }
+    }
+}
+
+impl Iterator for OptimizedExprTopDownIterator {
+    type Item = OptimizedExpr;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        let result = self.current.take();
+
+        if let Some(expr) = self.next.take() {
+            self.iterate_expr(expr);
+        } else if let Some(expr) = self.right_branches.pop() {
+            self.iterate_expr(expr);
+        }
+
+        result
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn rotate() {
+        let rules = {
+            use ast::Expr::*;
+            vec![Rule {
+                name: "rule".to_owned(),
+                ty: RuleType::Normal,
+                expr: box_tree!(Choice(
+                    Choice(
+                        Choice(Str(String::from("a")), Str(String::from("b"))),
+                        Str(String::from("c"))
+                    ),
+                    Str(String::from("d"))
+                )),
+            }]
+        };
+        let rotated = {
+            use optimizer::OptimizedExpr::*;
+            vec![OptimizedRule {
+                name: "rule".to_owned(),
+                ty: RuleType::Normal,
+                expr: box_tree!(Choice(
+                    Str(String::from("a")),
+                    Choice(
+                        Str(String::from("b")),
+                        Choice(Str(String::from("c")), Str(String::from("d")))
+                    )
+                )),
+            }]
+        };
+
+        assert_eq!(optimize(rules), rotated);
+    }
+
+    #[test]
+    fn skip() {
+        let rules = {
+            use ast::Expr::*;
+            vec![Rule {
+                name: "rule".to_owned(),
+                ty: RuleType::Atomic,
+                expr: box_tree!(Rep(Seq(
+                    NegPred(Choice(Str(String::from("a")), Str(String::from("b")))),
+                    Ident(String::from("ANY"))
+                ))),
+            }]
+        };
+        let skipped = vec![OptimizedRule {
+            name: "rule".to_owned(),
+            ty: RuleType::Atomic,
+            expr: OptimizedExpr::Skip(vec![String::from("a"), String::from("b")]),
+        }];
+
+        assert_eq!(optimize(rules), skipped);
+    }
+
+    #[test]
+    fn concat_strings() {
+        let rules = {
+            use ast::Expr::*;
+            vec![Rule {
+                name: "rule".to_owned(),
+                ty: RuleType::Atomic,
+                expr: box_tree!(Seq(
+                    Seq(Str(String::from("a")), Str(String::from("b"))),
+                    Seq(Str(String::from("c")), Str(String::from("d")))
+                )),
+            }]
+        };
+        let concatenated = vec![OptimizedRule {
+            name: "rule".to_owned(),
+            ty: RuleType::Atomic,
+            expr: OptimizedExpr::Str(String::from("abcd")),
+        }];
+
+        assert_eq!(optimize(rules), concatenated);
+    }
+
+    #[test]
+    fn unroll_loop_exact() {
+        let rules = vec![Rule {
+            name: "rule".to_owned(),
+            ty: RuleType::Atomic,
+            expr: Expr::RepExact(Box::new(Expr::Ident(String::from("a"))), 3),
+        }];
+        let unrolled = {
+            use optimizer::OptimizedExpr::*;
+            vec![OptimizedRule {
+                name: "rule".to_owned(),
+                ty: RuleType::Atomic,
+                expr: box_tree!(Seq(
+                    Ident(String::from("a")),
+                    Seq(Ident(String::from("a")), Ident(String::from("a")))
+                )),
+            }]
+        };
+
+        assert_eq!(optimize(rules), unrolled);
+    }
+
+    #[test]
+    fn unroll_loop_max() {
+        let rules = vec![Rule {
+            name: "rule".to_owned(),
+            ty: RuleType::Atomic,
+            expr: Expr::RepMax(Box::new(Expr::Str("a".to_owned())), 3),
+        }];
+        let unrolled = {
+            use optimizer::OptimizedExpr::*;
+            vec![OptimizedRule {
+                name: "rule".to_owned(),
+                ty: RuleType::Atomic,
+                expr: box_tree!(Seq(
+                    Opt(Str(String::from("a"))),
+                    Seq(Opt(Str(String::from("a"))), Opt(Str(String::from("a"))))
+                )),
+            }]
+        };
+
+        assert_eq!(optimize(rules), unrolled);
+    }
+
+    #[test]
+    fn unroll_loop_min() {
+        let rules = vec![Rule {
+            name: "rule".to_owned(),
+            ty: RuleType::Atomic,
+            expr: Expr::RepMin(Box::new(Expr::Str("a".to_owned())), 2),
+        }];
+        let unrolled = {
+            use optimizer::OptimizedExpr::*;
+            vec![OptimizedRule {
+                name: "rule".to_owned(),
+                ty: RuleType::Atomic,
+                expr: box_tree!(Seq(
+                    Str(String::from("a")),
+                    Seq(Str(String::from("a")), Rep(Str(String::from("a"))))
+                )),
+            }]
+        };
+
+        assert_eq!(optimize(rules), unrolled);
+    }
+
+    #[test]
+    fn unroll_loop_min_max() {
+        let rules = vec![Rule {
+            name: "rule".to_owned(),
+            ty: RuleType::Atomic,
+            expr: Expr::RepMinMax(Box::new(Expr::Str("a".to_owned())), 2, 3),
+        }];
+        let unrolled = {
+            use optimizer::OptimizedExpr::*;
+            vec![OptimizedRule {
+                name: "rule".to_owned(),
+                ty: RuleType::Atomic,
+                /* TODO possible room for improvement here:
+                 * if the sequences were rolled out in the opposite
+                 * order, we could further optimize the strings
+                 * in cases like this.
+                Str(String::from(("aa")),
+                Opt(Str(String::from("a")))
+                */
+                expr: box_tree!(Seq(
+                    Str(String::from("a")),
+                    Seq(Str(String::from("a")), Opt(Str(String::from("a"))))
+                )),
+            }]
+        };
+
+        assert_eq!(optimize(rules), unrolled);
+    }
+
+    #[test]
+    fn concat_insensitive_strings() {
+        let rules = {
+            use ast::Expr::*;
+            vec![Rule {
+                name: "rule".to_owned(),
+                ty: RuleType::Atomic,
+                expr: box_tree!(Seq(
+                    Seq(Insens(String::from("a")), Insens(String::from("b"))),
+                    Seq(Insens(String::from("c")), Insens(String::from("d")))
+                )),
+            }]
+        };
+        let concatenated = vec![OptimizedRule {
+            name: "rule".to_owned(),
+            ty: RuleType::Atomic,
+            expr: OptimizedExpr::Insens(String::from("abcd")),
+        }];
+
+        assert_eq!(optimize(rules), concatenated);
+    }
+
+    #[test]
+    fn long_common_sequence() {
+        let rules = {
+            use ast::Expr::*;
+            vec![Rule {
+                name: "rule".to_owned(),
+                ty: RuleType::Silent,
+                expr: box_tree!(Choice(
+                    Seq(
+                        Ident(String::from("a")),
+                        Seq(Ident(String::from("b")), Ident(String::from("c")))
+                    ),
+                    Seq(
+                        Seq(Ident(String::from("a")), Ident(String::from("b"))),
+                        Ident(String::from("d"))
+                    )
+                )),
+            }]
+        };
+        let optimized = {
+            use optimizer::OptimizedExpr::*;
+            vec![OptimizedRule {
+                name: "rule".to_owned(),
+                ty: RuleType::Silent,
+                expr: box_tree!(Seq(
+                    Ident(String::from("a")),
+                    Seq(
+                        Ident(String::from("b")),
+                        Choice(Ident(String::from("c")), Ident(String::from("d")))
+                    )
+                )),
+            }]
+        };
+
+        assert_eq!(optimize(rules), optimized);
+    }
+}
diff --git a/src/optimizer/restorer.rs b/src/optimizer/restorer.rs
new file mode 100644
index 0000000..34a710e
--- /dev/null
+++ b/src/optimizer/restorer.rs
@@ -0,0 +1,157 @@
+// pest. The Elegant Parser
+// Copyright (c) 2018 Dragoș Tiselice
+//
+// Licensed under the Apache License, Version 2.0
+// <LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0> or the MIT
+// license <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. All files in the project carrying such notice may not be copied,
+// modified, or distributed except according to those terms.
+use std::collections::HashMap;
+
+use optimizer::*;
+
+pub fn restore_on_err(
+    rule: OptimizedRule,
+    rules: &HashMap<String, OptimizedExpr>,
+) -> OptimizedRule {
+    match rule {
+        OptimizedRule { name, ty, expr } => {
+            let expr = expr.map_bottom_up(|expr| wrap_branching_exprs(expr, rules));
+
+            OptimizedRule { name, ty, expr }
+        }
+    }
+}
+
+fn wrap_branching_exprs(
+    expr: OptimizedExpr,
+    rules: &HashMap<String, OptimizedExpr>,
+) -> OptimizedExpr {
+    match expr {
+        OptimizedExpr::Opt(expr) => {
+            if child_modifies_state(&expr, rules, &mut HashMap::new()) {
+                OptimizedExpr::Opt(Box::new(OptimizedExpr::RestoreOnErr(expr)))
+            } else {
+                OptimizedExpr::Opt(expr)
+            }
+        }
+        OptimizedExpr::Choice(lhs, rhs) => {
+            let wrapped_lhs = if child_modifies_state(&lhs, rules, &mut HashMap::new()) {
+                Box::new(OptimizedExpr::RestoreOnErr(lhs))
+            } else {
+                lhs
+            };
+            let wrapped_rhs = if child_modifies_state(&rhs, rules, &mut HashMap::new()) {
+                Box::new(OptimizedExpr::RestoreOnErr(rhs))
+            } else {
+                rhs
+            };
+            OptimizedExpr::Choice(wrapped_lhs, wrapped_rhs)
+        }
+        OptimizedExpr::Rep(expr) => {
+            if child_modifies_state(&expr, rules, &mut HashMap::new()) {
+                OptimizedExpr::Rep(Box::new(OptimizedExpr::RestoreOnErr(expr)))
+            } else {
+                OptimizedExpr::Rep(expr)
+            }
+        }
+        _ => expr,
+    }
+}
+
+fn child_modifies_state(
+    expr: &OptimizedExpr,
+    rules: &HashMap<String, OptimizedExpr>,
+    cache: &mut HashMap<String, Option<bool>>,
+) -> bool {
+    expr.iter_top_down().any(|expr| match expr {
+        OptimizedExpr::Push(_) => true,
+        OptimizedExpr::Ident(ref name) if name == "DROP" => true,
+        OptimizedExpr::Ident(ref name) if name == "POP" => true,
+        OptimizedExpr::Ident(ref name) => match cache.get(name).cloned() {
+            Some(option) => match option {
+                Some(cached) => cached,
+                None => {
+                    cache.insert(name.to_owned(), Some(false));
+                    false
+                }
+            },
+            None => {
+                cache.insert(name.to_owned(), None);
+
+                let result = match rules.get(name) {
+                    Some(expr) => child_modifies_state(expr, rules, cache),
+                    None => false,
+                };
+
+                cache.insert(name.to_owned(), Some(result));
+
+                result
+            }
+        },
+        _ => false,
+    })
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use optimizer::OptimizedExpr::*;
+
+    #[test]
+    fn restore_no_stack_children() {
+        let rules = vec![OptimizedRule {
+            name: "rule".to_owned(),
+            ty: RuleType::Normal,
+            expr: box_tree!(Opt(Str("a".to_string()))),
+        }];
+
+        assert_eq!(
+            restore_on_err(rules[0].clone(), &to_hash_map(&rules)),
+            rules[0].clone()
+        );
+    }
+
+    #[test]
+    fn restore_with_child_stack_ops() {
+        let rules = vec![OptimizedRule {
+            name: "rule".to_owned(),
+            ty: RuleType::Normal,
+            expr: box_tree!(Rep(Push(Str("a".to_string())))),
+        }];
+
+        let restored = OptimizedRule {
+            name: "rule".to_owned(),
+            ty: RuleType::Normal,
+            expr: box_tree!(Rep(RestoreOnErr(Push(Str("a".to_string()))))),
+        };
+
+        assert_eq!(
+            restore_on_err(rules[0].clone(), &to_hash_map(&rules)),
+            restored
+        );
+    }
+
+    #[test]
+    fn restore_choice_branch_with_and_branch_without() {
+        let rules = vec![OptimizedRule {
+            name: "rule".to_owned(),
+            ty: RuleType::Normal,
+            expr: box_tree!(Choice(Push(Str("a".to_string())), Str("a".to_string()))),
+        }];
+
+        let restored = OptimizedRule {
+            name: "rule".to_owned(),
+            ty: RuleType::Normal,
+            expr: box_tree!(Choice(
+                RestoreOnErr(Push(Str("a".to_string()))),
+                Str("a".to_string())
+            )),
+        };
+
+        assert_eq!(
+            restore_on_err(rules[0].clone(), &to_hash_map(&rules)),
+            restored
+        );
+    }
+}
diff --git a/src/optimizer/rotater.rs b/src/optimizer/rotater.rs
new file mode 100644
index 0000000..3588738
--- /dev/null
+++ b/src/optimizer/rotater.rs
@@ -0,0 +1,45 @@
+// pest. The Elegant Parser
+// Copyright (c) 2018 Dragoș Tiselice
+//
+// Licensed under the Apache License, Version 2.0
+// <LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0> or the MIT
+// license <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. All files in the project carrying such notice may not be copied,
+// modified, or distributed except according to those terms.
+
+use ast::*;
+
+pub fn rotate(rule: Rule) -> Rule {
+    fn rotate_internal(expr: Expr) -> Expr {
+        match expr {
+            // TODO: Use box syntax when it gets stabilized.
+            Expr::Seq(lhs, rhs) => {
+                let lhs = *lhs;
+                match lhs {
+                    Expr::Seq(ll, lr) => {
+                        rotate_internal(Expr::Seq(ll, Box::new(Expr::Seq(lr, rhs))))
+                    }
+                    lhs => Expr::Seq(Box::new(lhs), rhs),
+                }
+            }
+            Expr::Choice(lhs, rhs) => {
+                let lhs = *lhs;
+                match lhs {
+                    Expr::Choice(ll, lr) => {
+                        rotate_internal(Expr::Choice(ll, Box::new(Expr::Choice(lr, rhs))))
+                    }
+                    lhs => Expr::Choice(Box::new(lhs), rhs),
+                }
+            }
+            expr => expr,
+        }
+    }
+
+    match rule {
+        Rule { name, ty, expr } => Rule {
+            name,
+            ty,
+            expr: expr.map_top_down(rotate_internal),
+        },
+    }
+}
diff --git a/src/optimizer/skipper.rs b/src/optimizer/skipper.rs
new file mode 100644
index 0000000..f55edc0
--- /dev/null
+++ b/src/optimizer/skipper.rs
@@ -0,0 +1,57 @@
+// pest. The Elegant Parser
+// Copyright (c) 2018 Dragoș Tiselice
+//
+// Licensed under the Apache License, Version 2.0
+// <LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0> or the MIT
+// license <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. All files in the project carrying such notice may not be copied,
+// modified, or distributed except according to those terms.
+
+use ast::*;
+
+pub fn skip(rule: Rule) -> Rule {
+    fn populate_choices(expr: Expr, mut choices: Vec<String>) -> Option<Expr> {
+        match expr {
+            Expr::Choice(lhs, rhs) => {
+                if let Expr::Str(string) = *lhs {
+                    choices.push(string);
+                    populate_choices(*rhs, choices)
+                } else {
+                    None
+                }
+            }
+            Expr::Str(string) => {
+                choices.push(string);
+                Some(Expr::Skip(choices))
+            }
+            _ => None,
+        }
+    }
+
+    match rule {
+        Rule { name, ty, expr } => Rule {
+            name,
+            ty,
+            expr: if ty == RuleType::Atomic {
+                expr.map_top_down(|expr| {
+                    // TODO: Use box syntax when it gets stabilized.
+                    if let Expr::Rep(expr) = expr.clone() {
+                        if let Expr::Seq(lhs, rhs) = *expr.clone() {
+                            if let (Expr::NegPred(expr), Expr::Ident(ident)) = (*lhs, *rhs) {
+                                if ident == "ANY" {
+                                    if let Some(expr) = populate_choices(*expr, vec![]) {
+                                        return expr;
+                                    }
+                                }
+                            }
+                        }
+                    };
+
+                    expr
+                })
+            } else {
+                expr
+            },
+        },
+    }
+}
diff --git a/src/optimizer/unroller.rs b/src/optimizer/unroller.rs
new file mode 100644
index 0000000..fff1733
--- /dev/null
+++ b/src/optimizer/unroller.rs
@@ -0,0 +1,67 @@
+// pest. The Elegant Parser
+// Copyright (c) 2018 Dragoș Tiselice
+//
+// Licensed under the Apache License, Version 2.0
+// <LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0> or the MIT
+// license <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. All files in the project carrying such notice may not be copied,
+// modified, or distributed except according to those terms.
+
+use ast::*;
+
+pub fn unroll(rule: Rule) -> Rule {
+    match rule {
+        Rule { name, ty, expr } => Rule {
+            name,
+            ty,
+            expr: expr.map_bottom_up(|expr| match expr {
+                Expr::RepOnce(expr) => Expr::Seq(expr.clone(), Box::new(Expr::Rep(expr))),
+                Expr::RepExact(expr, num) => (1..num + 1)
+                    .map(|_| *expr.clone())
+                    .rev()
+                    .fold(None, |rep, expr| match rep {
+                        None => Some(expr),
+                        Some(rep) => Some(Expr::Seq(Box::new(expr), Box::new(rep))),
+                    })
+                    .unwrap(),
+                Expr::RepMin(expr, min) => (1..min + 2)
+                    .map(|i| {
+                        if i <= min {
+                            *expr.clone()
+                        } else {
+                            Expr::Rep(expr.clone())
+                        }
+                    })
+                    .rev()
+                    .fold(None, |rep, expr| match rep {
+                        None => Some(expr),
+                        Some(rep) => Some(Expr::Seq(Box::new(expr), Box::new(rep))),
+                    })
+                    .unwrap(),
+                Expr::RepMax(expr, max) => (1..max + 1)
+                    .map(|_| Expr::Opt(expr.clone()))
+                    .rev()
+                    .fold(None, |rep, expr| match rep {
+                        None => Some(expr),
+                        Some(rep) => Some(Expr::Seq(Box::new(expr), Box::new(rep))),
+                    })
+                    .unwrap(),
+                Expr::RepMinMax(expr, min, max) => (1..max + 1)
+                    .map(|i| {
+                        if i <= min {
+                            *expr.clone()
+                        } else {
+                            Expr::Opt(expr.clone())
+                        }
+                    })
+                    .rev()
+                    .fold(None, |rep, expr| match rep {
+                        None => Some(expr),
+                        Some(rep) => Some(Expr::Seq(Box::new(expr), Box::new(rep))),
+                    })
+                    .unwrap(),
+                expr => expr,
+            }),
+        },
+    }
+}
diff --git a/src/parser.rs b/src/parser.rs
new file mode 100644
index 0000000..5f6f3b3
--- /dev/null
+++ b/src/parser.rs
@@ -0,0 +1,1488 @@
+// pest. The Elegant Parser
+// Copyright (c) 2018 Dragoș Tiselice
+//
+// Licensed under the Apache License, Version 2.0
+// <LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0> or the MIT
+// license <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. All files in the project carrying such notice may not be copied,
+// modified, or distributed except according to those terms.
+
+use std::char;
+use std::iter::Peekable;
+
+use pest::error::{Error, ErrorVariant};
+use pest::iterators::{Pair, Pairs};
+use pest::prec_climber::{Assoc, Operator, PrecClimber};
+use pest::{Parser, Span};
+
+use ast::{Expr, Rule as AstRule, RuleType};
+use validator;
+
+include!("grammar.rs");
+
+pub fn parse(rule: Rule, data: &str) -> Result<Pairs<Rule>, Error<Rule>> {
+    PestParser::parse(rule, data)
+}
+
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub struct ParserRule<'i> {
+    pub name: String,
+    pub span: Span<'i>,
+    pub ty: RuleType,
+    pub node: ParserNode<'i>,
+}
+
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub struct ParserNode<'i> {
+    pub expr: ParserExpr<'i>,
+    pub span: Span<'i>,
+}
+
+impl<'i> ParserNode<'i> {
+    pub fn filter_map_top_down<F, T>(self, mut f: F) -> Vec<T>
+    where
+        F: FnMut(ParserNode<'i>) -> Option<T>,
+    {
+        pub fn filter_internal<'i, F, T>(node: ParserNode<'i>, f: &mut F, result: &mut Vec<T>)
+        where
+            F: FnMut(ParserNode<'i>) -> Option<T>,
+        {
+            if let Some(value) = f(node.clone()) {
+                result.push(value);
+            }
+
+            match node.expr {
+                // TODO: Use box syntax when it gets stabilized.
+                ParserExpr::PosPred(node) => {
+                    filter_internal(*node, f, result);
+                }
+                ParserExpr::NegPred(node) => {
+                    filter_internal(*node, f, result);
+                }
+                ParserExpr::Seq(lhs, rhs) => {
+                    filter_internal(*lhs, f, result);
+                    filter_internal(*rhs, f, result);
+                }
+                ParserExpr::Choice(lhs, rhs) => {
+                    filter_internal(*lhs, f, result);
+                    filter_internal(*rhs, f, result);
+                }
+                ParserExpr::Rep(node) => {
+                    filter_internal(*node, f, result);
+                }
+                ParserExpr::RepOnce(node) => {
+                    filter_internal(*node, f, result);
+                }
+                ParserExpr::RepExact(node, _) => {
+                    filter_internal(*node, f, result);
+                }
+                ParserExpr::RepMin(node, _) => {
+                    filter_internal(*node, f, result);
+                }
+                ParserExpr::RepMax(node, _) => {
+                    filter_internal(*node, f, result);
+                }
+                ParserExpr::RepMinMax(node, ..) => {
+                    filter_internal(*node, f, result);
+                }
+                ParserExpr::Opt(node) => {
+                    filter_internal(*node, f, result);
+                }
+                ParserExpr::Push(node) => {
+                    filter_internal(*node, f, result);
+                }
+                _ => (),
+            }
+        }
+
+        let mut result = vec![];
+
+        filter_internal(self, &mut f, &mut result);
+
+        result
+    }
+}
+
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub enum ParserExpr<'i> {
+    Str(String),
+    Insens(String),
+    Range(String, String),
+    Ident(String),
+    PeekSlice(i32, Option<i32>),
+    PosPred(Box<ParserNode<'i>>),
+    NegPred(Box<ParserNode<'i>>),
+    Seq(Box<ParserNode<'i>>, Box<ParserNode<'i>>),
+    Choice(Box<ParserNode<'i>>, Box<ParserNode<'i>>),
+    Opt(Box<ParserNode<'i>>),
+    Rep(Box<ParserNode<'i>>),
+    RepOnce(Box<ParserNode<'i>>),
+    RepExact(Box<ParserNode<'i>>, u32),
+    RepMin(Box<ParserNode<'i>>, u32),
+    RepMax(Box<ParserNode<'i>>, u32),
+    RepMinMax(Box<ParserNode<'i>>, u32, u32),
+    Push(Box<ParserNode<'i>>),
+}
+
+fn convert_rule(rule: ParserRule) -> AstRule {
+    match rule {
+        ParserRule { name, ty, node, .. } => {
+            let expr = convert_node(node);
+
+            AstRule { name, ty, expr }
+        }
+    }
+}
+
+fn convert_node(node: ParserNode) -> Expr {
+    match node.expr {
+        ParserExpr::Str(string) => Expr::Str(string),
+        ParserExpr::Insens(string) => Expr::Insens(string),
+        ParserExpr::Range(start, end) => Expr::Range(start, end),
+        ParserExpr::Ident(ident) => Expr::Ident(ident),
+        ParserExpr::PeekSlice(start, end) => Expr::PeekSlice(start, end),
+        ParserExpr::PosPred(node) => Expr::PosPred(Box::new(convert_node(*node))),
+        ParserExpr::NegPred(node) => Expr::NegPred(Box::new(convert_node(*node))),
+        ParserExpr::Seq(node1, node2) => Expr::Seq(
+            Box::new(convert_node(*node1)),
+            Box::new(convert_node(*node2)),
+        ),
+        ParserExpr::Choice(node1, node2) => Expr::Choice(
+            Box::new(convert_node(*node1)),
+            Box::new(convert_node(*node2)),
+        ),
+        ParserExpr::Opt(node) => Expr::Opt(Box::new(convert_node(*node))),
+        ParserExpr::Rep(node) => Expr::Rep(Box::new(convert_node(*node))),
+        ParserExpr::RepOnce(node) => Expr::RepOnce(Box::new(convert_node(*node))),
+        ParserExpr::RepExact(node, num) => Expr::RepExact(Box::new(convert_node(*node)), num),
+        ParserExpr::RepMin(node, max) => Expr::RepMin(Box::new(convert_node(*node)), max),
+        ParserExpr::RepMax(node, max) => Expr::RepMax(Box::new(convert_node(*node)), max),
+        ParserExpr::RepMinMax(node, min, max) => {
+            Expr::RepMinMax(Box::new(convert_node(*node)), min, max)
+        }
+        ParserExpr::Push(node) => Expr::Push(Box::new(convert_node(*node))),
+    }
+}
+
+pub fn consume_rules(pairs: Pairs<Rule>) -> Result<Vec<AstRule>, Vec<Error<Rule>>> {
+    let rules = consume_rules_with_spans(pairs)?;
+    let errors = validator::validate_ast(&rules);
+    if errors.is_empty() {
+        Ok(rules.into_iter().map(convert_rule).collect())
+    } else {
+        Err(errors)
+    }
+}
+
+fn consume_rules_with_spans<'i>(
+    pairs: Pairs<'i, Rule>,
+) -> Result<Vec<ParserRule<'i>>, Vec<Error<Rule>>> {
+    let climber = PrecClimber::new(vec![
+        Operator::new(Rule::choice_operator, Assoc::Left),
+        Operator::new(Rule::sequence_operator, Assoc::Left),
+    ]);
+
+    pairs
+        .filter(|pair| pair.as_rule() == Rule::grammar_rule)
+        .map(|pair| {
+            let mut pairs = pair.into_inner().peekable();
+
+            let span = pairs.next().unwrap().as_span();
+            let name = span.as_str().to_owned();
+
+            pairs.next().unwrap(); // assignment_operator
+
+            let ty = if pairs.peek().unwrap().as_rule() != Rule::opening_brace {
+                match pairs.next().unwrap().as_rule() {
+                    Rule::silent_modifier => RuleType::Silent,
+                    Rule::atomic_modifier => RuleType::Atomic,
+                    Rule::compound_atomic_modifier => RuleType::CompoundAtomic,
+                    Rule::non_atomic_modifier => RuleType::NonAtomic,
+                    _ => unreachable!(),
+                }
+            } else {
+                RuleType::Normal
+            };
+
+            pairs.next().unwrap(); // opening_brace
+
+            let node = consume_expr(pairs.next().unwrap().into_inner().peekable(), &climber)?;
+
+            Ok(ParserRule {
+                name,
+                span,
+                ty,
+                node,
+            })
+        })
+        .collect()
+}
+
+fn consume_expr<'i>(
+    pairs: Peekable<Pairs<'i, Rule>>,
+    climber: &PrecClimber<Rule>,
+) -> Result<ParserNode<'i>, Vec<Error<Rule>>> {
+    fn unaries<'i>(
+        mut pairs: Peekable<Pairs<'i, Rule>>,
+        climber: &PrecClimber<Rule>,
+    ) -> Result<ParserNode<'i>, Vec<Error<Rule>>> {
+        let pair = pairs.next().unwrap();
+
+        let node = match pair.as_rule() {
+            Rule::opening_paren => {
+                let node = unaries(pairs, climber)?;
+                let end = node.span.end_pos();
+
+                ParserNode {
+                    expr: node.expr,
+                    span: pair.as_span().start_pos().span(&end),
+                }
+            }
+            Rule::positive_predicate_operator => {
+                let node = unaries(pairs, climber)?;
+                let end = node.span.end_pos();
+
+                ParserNode {
+                    expr: ParserExpr::PosPred(Box::new(node)),
+                    span: pair.as_span().start_pos().span(&end),
+                }
+            }
+            Rule::negative_predicate_operator => {
+                let node = unaries(pairs, climber)?;
+                let end = node.span.end_pos();
+
+                ParserNode {
+                    expr: ParserExpr::NegPred(Box::new(node)),
+                    span: pair.as_span().start_pos().span(&end),
+                }
+            }
+            other_rule => {
+                let node = match other_rule {
+                    Rule::expression => consume_expr(pair.into_inner().peekable(), climber)?,
+                    Rule::_push => {
+                        let start = pair.clone().as_span().start_pos();
+                        let mut pairs = pair.into_inner();
+                        pairs.next().unwrap(); // opening_paren
+                        let pair = pairs.next().unwrap();
+
+                        let node = consume_expr(pair.into_inner().peekable(), climber)?;
+                        let end = node.span.end_pos();
+
+                        ParserNode {
+                            expr: ParserExpr::Push(Box::new(node)),
+                            span: start.span(&end),
+                        }
+                    }
+                    Rule::peek_slice => {
+                        let mut pairs = pair.clone().into_inner();
+                        pairs.next().unwrap(); // opening_brack
+                        let pair_start = pairs.next().unwrap(); // .. or integer
+                        let start: i32 = match pair_start.as_rule() {
+                            Rule::range_operator => 0,
+                            Rule::integer => {
+                                pairs.next().unwrap(); // ..
+                                pair_start.as_str().parse().unwrap()
+                            }
+                            _ => unreachable!(),
+                        };
+                        let pair_end = pairs.next().unwrap(); // integer or }
+                        let end: Option<i32> = match pair_end.as_rule() {
+                            Rule::closing_brack => None,
+                            Rule::integer => {
+                                pairs.next().unwrap(); // }
+                                Some(pair_end.as_str().parse().unwrap())
+                            }
+                            _ => unreachable!(),
+                        };
+                        ParserNode {
+                            expr: ParserExpr::PeekSlice(start, end),
+                            span: pair.as_span(),
+                        }
+                    }
+                    Rule::identifier => ParserNode {
+                        expr: ParserExpr::Ident(pair.as_str().to_owned()),
+                        span: pair.clone().as_span(),
+                    },
+                    Rule::string => {
+                        let string = unescape(pair.as_str()).expect("incorrect string literal");
+                        ParserNode {
+                            expr: ParserExpr::Str(string[1..string.len() - 1].to_owned()),
+                            span: pair.clone().as_span(),
+                        }
+                    }
+                    Rule::insensitive_string => {
+                        let string = unescape(pair.as_str()).expect("incorrect string literal");
+                        ParserNode {
+                            expr: ParserExpr::Insens(string[2..string.len() - 1].to_owned()),
+                            span: pair.clone().as_span(),
+                        }
+                    }
+                    Rule::range => {
+                        let mut pairs = pair.into_inner();
+                        let pair = pairs.next().unwrap();
+                        let start = unescape(pair.as_str()).expect("incorrect char literal");
+                        let start_pos = pair.clone().as_span().start_pos();
+                        pairs.next();
+                        let pair = pairs.next().unwrap();
+                        let end = unescape(pair.as_str()).expect("incorrect char literal");
+                        let end_pos = pair.clone().as_span().end_pos();
+
+                        ParserNode {
+                            expr: ParserExpr::Range(
+                                start[1..start.len() - 1].to_owned(),
+                                end[1..end.len() - 1].to_owned(),
+                            ),
+                            span: start_pos.span(&end_pos),
+                        }
+                    }
+                    _ => unreachable!(),
+                };
+
+                pairs.fold(
+                    Ok(node),
+                    |node: Result<ParserNode<'i>, Vec<Error<Rule>>>, pair| {
+                        let node = node?;
+
+                        let node = match pair.as_rule() {
+                            Rule::optional_operator => {
+                                let start = node.span.start_pos();
+                                ParserNode {
+                                    expr: ParserExpr::Opt(Box::new(node)),
+                                    span: start.span(&pair.as_span().end_pos()),
+                                }
+                            }
+                            Rule::repeat_operator => {
+                                let start = node.span.start_pos();
+                                ParserNode {
+                                    expr: ParserExpr::Rep(Box::new(node)),
+                                    span: start.span(&pair.as_span().end_pos()),
+                                }
+                            }
+                            Rule::repeat_once_operator => {
+                                let start = node.span.start_pos();
+                                ParserNode {
+                                    expr: ParserExpr::RepOnce(Box::new(node)),
+                                    span: start.span(&pair.as_span().end_pos()),
+                                }
+                            }
+                            Rule::repeat_exact => {
+                                let mut inner = pair.clone().into_inner();
+
+                                inner.next().unwrap(); // opening_brace
+
+                                let number = inner.next().unwrap();
+                                let num = if let Ok(num) = number.as_str().parse::<u32>() {
+                                    num
+                                } else {
+                                    return Err(vec![Error::new_from_span(
+                                        ErrorVariant::CustomError {
+                                            message: "number cannot overflow u32".to_owned(),
+                                        },
+                                        number.as_span(),
+                                    )]);
+                                };
+
+                                if num == 0 {
+                                    let error: Error<Rule> = Error::new_from_span(
+                                        ErrorVariant::CustomError {
+                                            message: "cannot repeat 0 times".to_owned(),
+                                        },
+                                        number.as_span(),
+                                    );
+
+                                    return Err(vec![error]);
+                                }
+
+                                let start = node.span.start_pos();
+                                ParserNode {
+                                    expr: ParserExpr::RepExact(Box::new(node), num),
+                                    span: start.span(&pair.as_span().end_pos()),
+                                }
+                            }
+                            Rule::repeat_min => {
+                                let mut inner = pair.clone().into_inner();
+
+                                inner.next().unwrap(); // opening_brace
+
+                                let min_number = inner.next().unwrap();
+                                let min = if let Ok(min) = min_number.as_str().parse::<u32>() {
+                                    min
+                                } else {
+                                    return Err(vec![Error::new_from_span(
+                                        ErrorVariant::CustomError {
+                                            message: "number cannot overflow u32".to_owned(),
+                                        },
+                                        min_number.as_span(),
+                                    )]);
+                                };
+
+                                let start = node.span.start_pos();
+                                ParserNode {
+                                    expr: ParserExpr::RepMin(Box::new(node), min),
+                                    span: start.span(&pair.as_span().end_pos()),
+                                }
+                            }
+                            Rule::repeat_max => {
+                                let mut inner = pair.clone().into_inner();
+
+                                inner.next().unwrap(); // opening_brace
+                                inner.next().unwrap(); // comma
+
+                                let max_number = inner.next().unwrap();
+                                let max = if let Ok(max) = max_number.as_str().parse::<u32>() {
+                                    max
+                                } else {
+                                    return Err(vec![Error::new_from_span(
+                                        ErrorVariant::CustomError {
+                                            message: "number cannot overflow u32".to_owned(),
+                                        },
+                                        max_number.as_span(),
+                                    )]);
+                                };
+
+                                if max == 0 {
+                                    let error: Error<Rule> = Error::new_from_span(
+                                        ErrorVariant::CustomError {
+                                            message: "cannot repeat 0 times".to_owned(),
+                                        },
+                                        max_number.as_span(),
+                                    );
+
+                                    return Err(vec![error]);
+                                }
+
+                                let start = node.span.start_pos();
+                                ParserNode {
+                                    expr: ParserExpr::RepMax(Box::new(node), max),
+                                    span: start.span(&pair.as_span().end_pos()),
+                                }
+                            }
+                            Rule::repeat_min_max => {
+                                let mut inner = pair.clone().into_inner();
+
+                                inner.next().unwrap(); // opening_brace
+
+                                let min_number = inner.next().unwrap();
+                                let min = if let Ok(min) = min_number.as_str().parse::<u32>() {
+                                    min
+                                } else {
+                                    return Err(vec![Error::new_from_span(
+                                        ErrorVariant::CustomError {
+                                            message: "number cannot overflow u32".to_owned(),
+                                        },
+                                        min_number.as_span(),
+                                    )]);
+                                };
+
+                                inner.next().unwrap(); // comma
+
+                                let max_number = inner.next().unwrap();
+                                let max = if let Ok(max) = max_number.as_str().parse::<u32>() {
+                                    max
+                                } else {
+                                    return Err(vec![Error::new_from_span(
+                                        ErrorVariant::CustomError {
+                                            message: "number cannot overflow u32".to_owned(),
+                                        },
+                                        max_number.as_span(),
+                                    )]);
+                                };
+
+                                if max == 0 {
+                                    let error: Error<Rule> = Error::new_from_span(
+                                        ErrorVariant::CustomError {
+                                            message: "cannot repeat 0 times".to_owned(),
+                                        },
+                                        max_number.as_span(),
+                                    );
+
+                                    return Err(vec![error]);
+                                }
+
+                                let start = node.span.start_pos();
+                                ParserNode {
+                                    expr: ParserExpr::RepMinMax(Box::new(node), min, max),
+                                    span: start.span(&pair.as_span().end_pos()),
+                                }
+                            }
+                            Rule::closing_paren => {
+                                let start = node.span.start_pos();
+
+                                ParserNode {
+                                    expr: node.expr,
+                                    span: start.span(&pair.as_span().end_pos()),
+                                }
+                            }
+                            _ => unreachable!(),
+                        };
+
+                        Ok(node)
+                    },
+                )?
+            }
+        };
+
+        Ok(node)
+    }
+
+    let term = |pair: Pair<'i, Rule>| unaries(pair.into_inner().peekable(), climber);
+    let infix = |lhs: Result<ParserNode<'i>, Vec<Error<Rule>>>,
+                 op: Pair<'i, Rule>,
+                 rhs: Result<ParserNode<'i>, Vec<Error<Rule>>>| match op.as_rule() {
+        Rule::sequence_operator => {
+            let lhs = lhs?;
+            let rhs = rhs?;
+
+            let start = lhs.span.start_pos();
+            let end = rhs.span.end_pos();
+
+            Ok(ParserNode {
+                expr: ParserExpr::Seq(Box::new(lhs), Box::new(rhs)),
+                span: start.span(&end),
+            })
+        }
+        Rule::choice_operator => {
+            let lhs = lhs?;
+            let rhs = rhs?;
+
+            let start = lhs.span.start_pos();
+            let end = rhs.span.end_pos();
+
+            Ok(ParserNode {
+                expr: ParserExpr::Choice(Box::new(lhs), Box::new(rhs)),
+                span: start.span(&end),
+            })
+        }
+        _ => unreachable!(),
+    };
+
+    climber.climb(pairs, term, infix)
+}
+
+fn unescape(string: &str) -> Option<String> {
+    let mut result = String::new();
+    let mut chars = string.chars();
+
+    loop {
+        match chars.next() {
+            Some('\\') => match chars.next()? {
+                '"' => result.push('"'),
+                '\\' => result.push('\\'),
+                'r' => result.push('\r'),
+                'n' => result.push('\n'),
+                't' => result.push('\t'),
+                '0' => result.push('\0'),
+                '\'' => result.push('\''),
+                'x' => {
+                    let string: String = chars.clone().take(2).collect();
+
+                    if string.len() != 2 {
+                        return None;
+                    }
+
+                    for _ in 0..string.len() {
+                        chars.next()?;
+                    }
+
+                    let value = u8::from_str_radix(&string, 16).ok()?;
+
+                    result.push(char::from(value));
+                }
+                'u' => {
+                    if chars.next()? != '{' {
+                        return None;
+                    }
+
+                    let string: String = chars.clone().take_while(|c| *c != '}').collect();
+
+                    if string.len() < 2 || 6 < string.len() {
+                        return None;
+                    }
+
+                    for _ in 0..string.len() + 1 {
+                        chars.next()?;
+                    }
+
+                    let value = u32::from_str_radix(&string, 16).ok()?;
+
+                    result.push(char::from_u32(value)?);
+                }
+                _ => return None,
+            },
+            Some(c) => result.push(c),
+            None => return Some(result),
+        };
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::super::unwrap_or_report;
+    use super::*;
+
+    #[test]
+    fn rules() {
+        parses_to! {
+            parser: PestParser,
+            input: "a = { b } c = { d }",
+            rule: Rule::grammar_rules,
+            tokens: [
+                grammar_rule(0, 9, [
+                    identifier(0, 1),
+                    assignment_operator(2, 3),
+                    opening_brace(4, 5),
+                    expression(6, 8, [
+                        term(6, 8, [
+                            identifier(6, 7)
+                        ])
+                    ]),
+                    closing_brace(8, 9)
+                ]),
+                grammar_rule(10, 19, [
+                    identifier(10, 11),
+                    assignment_operator(12, 13),
+                    opening_brace(14, 15),
+                    expression(16, 18, [
+                        term(16, 18, [
+                            identifier(16, 17)
+                        ])
+                    ]),
+                    closing_brace(18, 19)
+                ])
+            ]
+        };
+    }
+
+    #[test]
+    fn rule() {
+        parses_to! {
+            parser: PestParser,
+            input: "a = ! { b ~ c }",
+            rule: Rule::grammar_rule,
+            tokens: [
+                grammar_rule(0, 15, [
+                    identifier(0, 1),
+                    assignment_operator(2, 3),
+                    non_atomic_modifier(4, 5),
+                    opening_brace(6, 7),
+                    expression(8, 14, [
+                        term(8, 10, [
+                            identifier(8, 9)
+                        ]),
+                        sequence_operator(10, 11),
+                        term(12, 14, [
+                            identifier(12, 13)
+                        ])
+                    ]),
+                    closing_brace(14, 15)
+                ])
+            ]
+        };
+    }
+
+    #[test]
+    fn expression() {
+        parses_to! {
+            parser: PestParser,
+            input: "_a | 'a'..'b' ~ !^\"abc\" ~ (d | e)*?",
+            rule: Rule::expression,
+            tokens: [
+                expression(0, 35, [
+                    term(0, 3, [
+                        identifier(0, 2)
+                    ]),
+                    choice_operator(3, 4),
+                    term(5, 14, [
+                        range(5, 13, [
+                            character(5, 8, [
+                                single_quote(5, 6),
+                                inner_chr(6, 7),
+                                single_quote(7, 8)
+                            ]),
+                            range_operator(8, 10),
+                            character(10, 13, [
+                                single_quote(10, 11),
+                                inner_chr(11, 12),
+                                single_quote(12, 13)
+                            ])
+                        ])
+                    ]),
+                    sequence_operator(14, 15),
+                    term(16, 24, [
+                        negative_predicate_operator(16, 17),
+                        insensitive_string(17, 23, [
+                            string(18, 23, [
+                                quote(18, 19),
+                                inner_str(19, 22),
+                                quote(22, 23)
+                            ])
+                        ])
+                    ]),
+                    sequence_operator(24, 25),
+                    term(26, 35, [
+                        opening_paren(26, 27),
+                        expression(27, 32, [
+                            term(27, 29, [
+                                identifier(27, 28)
+                            ]),
+                            choice_operator(29, 30),
+                            term(31, 32, [
+                                identifier(31, 32)
+                            ])
+                        ]),
+                        closing_paren(32, 33),
+                        repeat_operator(33, 34),
+                        optional_operator(34, 35)
+                    ])
+                ])
+            ]
+        };
+    }
+
+    #[test]
+    fn repeat_exact() {
+        parses_to! {
+            parser: PestParser,
+            input: "{1}",
+            rule: Rule::repeat_exact,
+            tokens: [
+                repeat_exact(0, 3, [
+                    opening_brace(0, 1),
+                    number(1, 2),
+                    closing_brace(2, 3)
+                ])
+            ]
+        };
+    }
+
+    #[test]
+    fn repeat_min() {
+        parses_to! {
+            parser: PestParser,
+            input: "{2,}",
+            rule: Rule::repeat_min,
+            tokens: [
+                repeat_min(0, 4, [
+                    opening_brace(0,1),
+                    number(1,2),
+                    comma(2,3),
+                    closing_brace(3,4)
+                ])
+            ]
+        }
+    }
+
+    #[test]
+    fn repeat_max() {
+        parses_to! {
+            parser: PestParser,
+            input: "{, 3}",
+            rule: Rule::repeat_max,
+            tokens: [
+                repeat_max(0, 5, [
+                    opening_brace(0,1),
+                    comma(1,2),
+                    number(3,4),
+                    closing_brace(4,5)
+                ])
+            ]
+        }
+    }
+
+    #[test]
+    fn repeat_min_max() {
+        parses_to! {
+            parser: PestParser,
+            input: "{1, 2}",
+            rule: Rule::repeat_min_max,
+            tokens: [
+                repeat_min_max(0, 6, [
+                    opening_brace(0, 1),
+                    number(1, 2),
+                    comma(2, 3),
+                    number(4, 5),
+                    closing_brace(5, 6)
+                ])
+            ]
+        };
+    }
+
+    #[test]
+    fn push() {
+        parses_to! {
+            parser: PestParser,
+            input: "PUSH ( a )",
+            rule: Rule::_push,
+            tokens: [
+                _push(0, 10, [
+                    opening_paren(5, 6),
+                    expression(7, 9, [
+                        term(7, 9, [
+                            identifier(7, 8)
+                        ])
+                    ]),
+                    closing_paren(9, 10)
+                ])
+            ]
+        };
+    }
+
+    #[test]
+    fn peek_slice_all() {
+        parses_to! {
+            parser: PestParser,
+            input: "PEEK[..]",
+            rule: Rule::peek_slice,
+            tokens: [
+                peek_slice(0, 8, [
+                    opening_brack(4, 5),
+                    range_operator(5, 7),
+                    closing_brack(7, 8)
+                ])
+            ]
+        };
+    }
+
+    #[test]
+    fn peek_slice_start() {
+        parses_to! {
+            parser: PestParser,
+            input: "PEEK[1..]",
+            rule: Rule::peek_slice,
+            tokens: [
+                peek_slice(0, 9, [
+                    opening_brack(4, 5),
+                    integer(5, 6),
+                    range_operator(6, 8),
+                    closing_brack(8, 9)
+                ])
+            ]
+        };
+    }
+
+    #[test]
+    fn peek_slice_end() {
+        parses_to! {
+            parser: PestParser,
+            input: "PEEK[ ..-1]",
+            rule: Rule::peek_slice,
+            tokens: [
+                peek_slice(0, 11, [
+                    opening_brack(4, 5),
+                    range_operator(6, 8),
+                    integer(8, 10),
+                    closing_brack(10, 11)
+                ])
+            ]
+        };
+    }
+
+    #[test]
+    fn peek_slice_start_end() {
+        parses_to! {
+            parser: PestParser,
+            input: "PEEK[-5..10]",
+            rule: Rule::peek_slice,
+            tokens: [
+                peek_slice(0, 12, [
+                    opening_brack(4, 5),
+                    integer(5, 7),
+                    range_operator(7, 9),
+                    integer(9, 11),
+                    closing_brack(11, 12)
+                ])
+            ]
+        };
+    }
+
+    #[test]
+    fn identifier() {
+        parses_to! {
+            parser: PestParser,
+            input: "_a8943",
+            rule: Rule::identifier,
+            tokens: [
+                identifier(0, 6)
+            ]
+        };
+    }
+
+    #[test]
+    fn string() {
+        parses_to! {
+            parser: PestParser,
+            input: "\"aaaaa\\n\\r\\t\\\\\\0\\'\\\"\\x0F\\u{123abC}\\u{12}aaaaa\"",
+            rule: Rule::string,
+            tokens: [
+                string(0, 46, [
+                    quote(0, 1),
+                    inner_str(1, 45),
+                    quote(45, 46)
+                ])
+            ]
+        };
+    }
+
+    #[test]
+    fn insensitive_string() {
+        parses_to! {
+            parser: PestParser,
+            input: "^  \"\\\"hi\"",
+            rule: Rule::insensitive_string,
+            tokens: [
+                insensitive_string(0, 9, [
+                    string(3, 9, [
+                        quote(3, 4),
+                        inner_str(4, 8),
+                        quote(8, 9)
+                    ])
+                ])
+            ]
+        };
+    }
+
+    #[test]
+    fn range() {
+        parses_to! {
+            parser: PestParser,
+            input: "'\\n' .. '\\x1a'",
+            rule: Rule::range,
+            tokens: [
+                range(0, 14, [
+                    character(0, 4, [
+                        single_quote(0, 1),
+                        inner_chr(1, 3),
+                        single_quote(3, 4)
+                    ]),
+                    range_operator(5, 7),
+                    character(8, 14, [
+                        single_quote(8, 9),
+                        inner_chr(9, 13),
+                        single_quote(13, 14)
+                    ])
+                ])
+            ]
+        };
+    }
+
+    #[test]
+    fn character() {
+        parses_to! {
+            parser: PestParser,
+            input: "'\\u{123abC}'",
+            rule: Rule::character,
+            tokens: [
+                character(0, 12, [
+                    single_quote(0, 1),
+                    inner_chr(1, 11),
+                    single_quote(11, 12)
+                ])
+            ]
+        };
+    }
+
+    #[test]
+    fn number() {
+        parses_to! {
+            parser: PestParser,
+            input: "0123",
+            rule: Rule::number,
+            tokens: [
+                number(0, 4)
+            ]
+        };
+    }
+
+    #[test]
+    fn comment() {
+        parses_to! {
+            parser: PestParser,
+            input: "a ~    // asda\n b",
+            rule: Rule::expression,
+            tokens: [
+                expression(0, 17, [
+                    term(0, 2, [
+                        identifier(0, 1)
+                    ]),
+                    sequence_operator(2, 3),
+                    term(16, 17, [
+                        identifier(16, 17)
+                    ])
+                ])
+            ]
+        };
+    }
+
+    #[test]
+    fn wrong_identifier() {
+        fails_with! {
+            parser: PestParser,
+            input: "0",
+            rule: Rule::grammar_rules,
+            positives: vec![Rule::identifier],
+            negatives: vec![],
+            pos: 0
+        };
+    }
+
+    #[test]
+    fn missing_assignment_operator() {
+        fails_with! {
+            parser: PestParser,
+            input: "a {}",
+            rule: Rule::grammar_rules,
+            positives: vec![Rule::assignment_operator],
+            negatives: vec![],
+            pos: 2
+        };
+    }
+
+    #[test]
+    fn wrong_modifier() {
+        fails_with! {
+            parser: PestParser,
+            input: "a = *{}",
+            rule: Rule::grammar_rules,
+            positives: vec![
+                Rule::opening_brace,
+                Rule::silent_modifier,
+                Rule::atomic_modifier,
+                Rule::compound_atomic_modifier,
+                Rule::non_atomic_modifier
+            ],
+            negatives: vec![],
+            pos: 4
+        };
+    }
+
+    #[test]
+    fn missing_opening_brace() {
+        fails_with! {
+            parser: PestParser,
+            input: "a = _",
+            rule: Rule::grammar_rules,
+            positives: vec![Rule::opening_brace],
+            negatives: vec![],
+            pos: 5
+        };
+    }
+
+    #[test]
+    fn empty_rule() {
+        fails_with! {
+            parser: PestParser,
+            input: "a = {}",
+            rule: Rule::grammar_rules,
+            positives: vec![Rule::term],
+            negatives: vec![],
+            pos: 5
+        };
+    }
+
+    #[test]
+    fn missing_rhs() {
+        fails_with! {
+            parser: PestParser,
+            input: "a = { b ~ }",
+            rule: Rule::grammar_rules,
+            positives: vec![Rule::term],
+            negatives: vec![],
+            pos: 10
+        };
+    }
+
+    #[test]
+    fn wrong_op() {
+        fails_with! {
+            parser: PestParser,
+            input: "a = { b % }",
+            rule: Rule::grammar_rules,
+            positives: vec![
+                Rule::opening_brace,
+                Rule::closing_brace,
+                Rule::sequence_operator,
+                Rule::choice_operator,
+                Rule::optional_operator,
+                Rule::repeat_operator,
+                Rule::repeat_once_operator
+            ],
+            negatives: vec![],
+            pos: 8
+        };
+    }
+
+    #[test]
+    fn missing_closing_paren() {
+        fails_with! {
+            parser: PestParser,
+            input: "a = { (b }",
+            rule: Rule::grammar_rules,
+            positives: vec![
+                Rule::opening_brace,
+                Rule::closing_paren,
+                Rule::sequence_operator,
+                Rule::choice_operator,
+                Rule::optional_operator,
+                Rule::repeat_operator,
+                Rule::repeat_once_operator
+            ],
+            negatives: vec![],
+            pos: 9
+        };
+    }
+
+    #[test]
+    fn missing_term() {
+        fails_with! {
+            parser: PestParser,
+            input: "a = { ! }",
+            rule: Rule::grammar_rules,
+            positives: vec![
+                Rule::opening_paren,
+                Rule::positive_predicate_operator,
+                Rule::negative_predicate_operator,
+                Rule::_push,
+                Rule::peek_slice,
+                Rule::identifier,
+                Rule::insensitive_string,
+                Rule::quote,
+                Rule::single_quote
+            ],
+            negatives: vec![],
+            pos: 8
+        };
+    }
+
+    #[test]
+    fn string_missing_ending_quote() {
+        fails_with! {
+            parser: PestParser,
+            input: "a = { \" }",
+            rule: Rule::grammar_rules,
+            positives: vec![Rule::quote],
+            negatives: vec![],
+            pos: 9
+        };
+    }
+
+    #[test]
+    fn insensitive_missing_string() {
+        fails_with! {
+            parser: PestParser,
+            input: "a = { ^ }",
+            rule: Rule::grammar_rules,
+            positives: vec![Rule::quote],
+            negatives: vec![],
+            pos: 8
+        };
+    }
+
+    #[test]
+    fn char_missing_ending_single_quote() {
+        fails_with! {
+            parser: PestParser,
+            input: "a = { \' }",
+            rule: Rule::grammar_rules,
+            positives: vec![Rule::single_quote],
+            negatives: vec![],
+            pos: 8
+        };
+    }
+
+    #[test]
+    fn range_missing_range_operator() {
+        fails_with! {
+            parser: PestParser,
+            input: "a = { \'a\' }",
+            rule: Rule::grammar_rules,
+            positives: vec![Rule::range_operator],
+            negatives: vec![],
+            pos: 10
+        };
+    }
+
+    #[test]
+    fn wrong_postfix() {
+        fails_with! {
+            parser: PestParser,
+            input: "a = { a& }",
+            rule: Rule::grammar_rules,
+            positives: vec![
+                Rule::opening_brace,
+                Rule::closing_brace,
+                Rule::sequence_operator,
+                Rule::choice_operator,
+                Rule::optional_operator,
+                Rule::repeat_operator,
+                Rule::repeat_once_operator
+            ],
+            negatives: vec![],
+            pos: 7
+        };
+    }
+
+    #[test]
+    fn ast() {
+        let input =
+            "rule = _{ a{1} ~ \"a\"{3,} ~ b{, 2} ~ \"b\"{1, 2} | !(^\"c\" | PUSH('d'..'e'))?* }";
+
+        let pairs = PestParser::parse(Rule::grammar_rules, input).unwrap();
+        let ast = consume_rules_with_spans(pairs).unwrap();
+        let ast: Vec<_> = ast.into_iter().map(|rule| convert_rule(rule)).collect();
+
+        assert_eq!(
+            ast,
+            vec![AstRule {
+                name: "rule".to_owned(),
+                ty: RuleType::Silent,
+                expr: Expr::Choice(
+                    Box::new(Expr::Seq(
+                        Box::new(Expr::Seq(
+                            Box::new(Expr::Seq(
+                                Box::new(Expr::RepExact(Box::new(Expr::Ident("a".to_owned())), 1)),
+                                Box::new(Expr::RepMin(Box::new(Expr::Str("a".to_owned())), 3))
+                            )),
+                            Box::new(Expr::RepMax(Box::new(Expr::Ident("b".to_owned())), 2))
+                        )),
+                        Box::new(Expr::RepMinMax(Box::new(Expr::Str("b".to_owned())), 1, 2))
+                    )),
+                    Box::new(Expr::NegPred(Box::new(Expr::Rep(Box::new(Expr::Opt(
+                        Box::new(Expr::Choice(
+                            Box::new(Expr::Insens("c".to_owned())),
+                            Box::new(Expr::Push(Box::new(Expr::Range(
+                                "d".to_owned(),
+                                "e".to_owned()
+                            ))))
+                        ))
+                    ))))))
+                )
+            },]
+        );
+    }
+
+    #[test]
+    fn ast_peek_slice() {
+        let input = "rule = _{ PEEK[-04..] ~ PEEK[..3] }";
+
+        let pairs = PestParser::parse(Rule::grammar_rules, input).unwrap();
+        let ast = consume_rules_with_spans(pairs).unwrap();
+        let ast: Vec<_> = ast.into_iter().map(|rule| convert_rule(rule)).collect();
+
+        assert_eq!(
+            ast,
+            vec![AstRule {
+                name: "rule".to_owned(),
+                ty: RuleType::Silent,
+                expr: Expr::Seq(
+                    Box::new(Expr::PeekSlice(-4, None)),
+                    Box::new(Expr::PeekSlice(0, Some(3))),
+                )
+            }],
+        );
+    }
+
+    #[test]
+    #[should_panic(expected = "grammar error
+
+ --> 1:13
+  |
+1 | rule = { \"\"{4294967297} }
+  |             ^--------^
+  |
+  = number cannot overflow u32")]
+    fn repeat_exact_overflow() {
+        let input = "rule = { \"\"{4294967297} }";
+
+        let pairs = PestParser::parse(Rule::grammar_rules, input).unwrap();
+        unwrap_or_report(consume_rules_with_spans(pairs));
+    }
+
+    #[test]
+    #[should_panic(expected = "grammar error
+
+ --> 1:13
+  |
+1 | rule = { \"\"{0} }
+  |             ^
+  |
+  = cannot repeat 0 times")]
+    fn repeat_exact_zero() {
+        let input = "rule = { \"\"{0} }";
+
+        let pairs = PestParser::parse(Rule::grammar_rules, input).unwrap();
+        unwrap_or_report(consume_rules_with_spans(pairs));
+    }
+
+    #[test]
+    #[should_panic(expected = "grammar error
+
+ --> 1:13
+  |
+1 | rule = { \"\"{4294967297,} }
+  |             ^--------^
+  |
+  = number cannot overflow u32")]
+    fn repeat_min_overflow() {
+        let input = "rule = { \"\"{4294967297,} }";
+
+        let pairs = PestParser::parse(Rule::grammar_rules, input).unwrap();
+        unwrap_or_report(consume_rules_with_spans(pairs));
+    }
+
+    #[test]
+    #[should_panic(expected = "grammar error
+
+ --> 1:14
+  |
+1 | rule = { \"\"{,4294967297} }
+  |              ^--------^
+  |
+  = number cannot overflow u32")]
+    fn repeat_max_overflow() {
+        let input = "rule = { \"\"{,4294967297} }";
+
+        let pairs = PestParser::parse(Rule::grammar_rules, input).unwrap();
+        unwrap_or_report(consume_rules_with_spans(pairs));
+    }
+
+    #[test]
+    #[should_panic(expected = "grammar error
+
+ --> 1:14
+  |
+1 | rule = { \"\"{,0} }
+  |              ^
+  |
+  = cannot repeat 0 times")]
+    fn repeat_max_zero() {
+        let input = "rule = { \"\"{,0} }";
+
+        let pairs = PestParser::parse(Rule::grammar_rules, input).unwrap();
+        unwrap_or_report(consume_rules_with_spans(pairs));
+    }
+
+    #[test]
+    #[should_panic(expected = "grammar error
+
+ --> 1:13
+  |
+1 | rule = { \"\"{4294967297,4294967298} }
+  |             ^--------^
+  |
+  = number cannot overflow u32")]
+    fn repeat_min_max_overflow() {
+        let input = "rule = { \"\"{4294967297,4294967298} }";
+
+        let pairs = PestParser::parse(Rule::grammar_rules, input).unwrap();
+        unwrap_or_report(consume_rules_with_spans(pairs));
+    }
+
+    #[test]
+    #[should_panic(expected = "grammar error
+
+ --> 1:15
+  |
+1 | rule = { \"\"{0,0} }
+  |               ^
+  |
+  = cannot repeat 0 times")]
+    fn repeat_min_max_zero() {
+        let input = "rule = { \"\"{0,0} }";
+
+        let pairs = PestParser::parse(Rule::grammar_rules, input).unwrap();
+        unwrap_or_report(consume_rules_with_spans(pairs));
+    }
+
+    #[test]
+    fn unescape_all() {
+        let string = r"a\nb\x55c\u{111}d";
+
+        assert_eq!(unescape(string), Some("a\nb\x55c\u{111}d".to_owned()));
+    }
+
+    #[test]
+    fn unescape_empty_escape() {
+        let string = r"\";
+
+        assert_eq!(unescape(string), None);
+    }
+
+    #[test]
+    fn unescape_wrong_escape() {
+        let string = r"\w";
+
+        assert_eq!(unescape(string), None);
+    }
+
+    #[test]
+    fn unescape_backslash() {
+        let string = "\\\\";
+        assert_eq!(unescape(string), Some("\\".to_owned()));
+    }
+
+    #[test]
+    fn unescape_return() {
+        let string = "\\r";
+        assert_eq!(unescape(string), Some("\r".to_owned()));
+    }
+
+    #[test]
+    fn unescape_tab() {
+        let string = "\\t";
+        assert_eq!(unescape(string), Some("\t".to_owned()));
+    }
+
+    #[test]
+    fn unescape_null() {
+        let string = "\\0";
+        assert_eq!(unescape(string), Some("\0".to_owned()));
+    }
+
+    #[test]
+    fn unescape_single_quote() {
+        let string = "\\'";
+        assert_eq!(unescape(string), Some("\'".to_owned()));
+    }
+
+    #[test]
+    fn unescape_wrong_byte() {
+        let string = r"\xfg";
+
+        assert_eq!(unescape(string), None);
+    }
+
+    #[test]
+    fn unescape_short_byte() {
+        let string = r"\xf";
+
+        assert_eq!(unescape(string), None);
+    }
+
+    #[test]
+    fn unescape_no_open_brace_unicode() {
+        let string = r"\u11";
+
+        assert_eq!(unescape(string), None);
+    }
+
+    #[test]
+    fn unescape_no_close_brace_unicode() {
+        let string = r"\u{11";
+
+        assert_eq!(unescape(string), None);
+    }
+
+    #[test]
+    fn unescape_short_unicode() {
+        let string = r"\u{1}";
+
+        assert_eq!(unescape(string), None);
+    }
+
+    #[test]
+    fn unescape_long_unicode() {
+        let string = r"\u{1111111}";
+
+        assert_eq!(unescape(string), None);
+    }
+}
diff --git a/src/validator.rs b/src/validator.rs
new file mode 100644
index 0000000..a358dbe
--- /dev/null
+++ b/src/validator.rs
@@ -0,0 +1,851 @@
+// pest. The Elegant Parser
+// Copyright (c) 2018 Dragoș Tiselice
+//
+// Licensed under the Apache License, Version 2.0
+// <LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0> or the MIT
+// license <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. All files in the project carrying such notice may not be copied,
+// modified, or distributed except according to those terms.
+
+use std::collections::{HashMap, HashSet};
+
+use pest::error::{Error, ErrorVariant, InputLocation};
+use pest::iterators::Pairs;
+use pest::Span;
+
+use parser::{ParserExpr, ParserNode, ParserRule, Rule};
+use UNICODE_PROPERTY_NAMES;
+
+#[allow(clippy::needless_pass_by_value)]
+pub fn validate_pairs<'i>(pairs: Pairs<'i, Rule>) -> Result<Vec<&'i str>, Vec<Error<Rule>>> {
+    let mut rust_keywords = HashSet::new();
+    rust_keywords.insert("abstract");
+    rust_keywords.insert("alignof");
+    rust_keywords.insert("as");
+    rust_keywords.insert("become");
+    rust_keywords.insert("box");
+    rust_keywords.insert("break");
+    rust_keywords.insert("const");
+    rust_keywords.insert("continue");
+    rust_keywords.insert("crate");
+    rust_keywords.insert("do");
+    rust_keywords.insert("else");
+    rust_keywords.insert("enum");
+    rust_keywords.insert("extern");
+    rust_keywords.insert("false");
+    rust_keywords.insert("final");
+    rust_keywords.insert("fn");
+    rust_keywords.insert("for");
+    rust_keywords.insert("if");
+    rust_keywords.insert("impl");
+    rust_keywords.insert("in");
+    rust_keywords.insert("let");
+    rust_keywords.insert("loop");
+    rust_keywords.insert("macro");
+    rust_keywords.insert("match");
+    rust_keywords.insert("mod");
+    rust_keywords.insert("move");
+    rust_keywords.insert("mut");
+    rust_keywords.insert("offsetof");
+    rust_keywords.insert("override");
+    rust_keywords.insert("priv");
+    rust_keywords.insert("proc");
+    rust_keywords.insert("pure");
+    rust_keywords.insert("pub");
+    rust_keywords.insert("ref");
+    rust_keywords.insert("return");
+    rust_keywords.insert("Self");
+    rust_keywords.insert("self");
+    rust_keywords.insert("sizeof");
+    rust_keywords.insert("static");
+    rust_keywords.insert("struct");
+    rust_keywords.insert("super");
+    rust_keywords.insert("trait");
+    rust_keywords.insert("true");
+    rust_keywords.insert("type");
+    rust_keywords.insert("typeof");
+    rust_keywords.insert("unsafe");
+    rust_keywords.insert("unsized");
+    rust_keywords.insert("use");
+    rust_keywords.insert("virtual");
+    rust_keywords.insert("where");
+    rust_keywords.insert("while");
+    rust_keywords.insert("yield");
+
+    let mut pest_keywords = HashSet::new();
+    pest_keywords.insert("_");
+    pest_keywords.insert("ANY");
+    pest_keywords.insert("DROP");
+    pest_keywords.insert("EOI");
+    pest_keywords.insert("PEEK");
+    pest_keywords.insert("PEEK_ALL");
+    pest_keywords.insert("POP");
+    pest_keywords.insert("POP_ALL");
+    pest_keywords.insert("PUSH");
+    pest_keywords.insert("SOI");
+
+    let mut builtins = HashSet::new();
+    builtins.insert("ANY");
+    builtins.insert("DROP");
+    builtins.insert("EOI");
+    builtins.insert("PEEK");
+    builtins.insert("PEEK_ALL");
+    builtins.insert("POP");
+    builtins.insert("POP_ALL");
+    builtins.insert("SOI");
+    builtins.insert("ASCII_DIGIT");
+    builtins.insert("ASCII_NONZERO_DIGIT");
+    builtins.insert("ASCII_BIN_DIGIT");
+    builtins.insert("ASCII_OCT_DIGIT");
+    builtins.insert("ASCII_HEX_DIGIT");
+    builtins.insert("ASCII_ALPHA_LOWER");
+    builtins.insert("ASCII_ALPHA_UPPER");
+    builtins.insert("ASCII_ALPHA");
+    builtins.insert("ASCII_ALPHANUMERIC");
+    builtins.insert("ASCII");
+    builtins.insert("NEWLINE");
+    builtins.extend(UNICODE_PROPERTY_NAMES);
+
+    let definitions: Vec<_> = pairs
+        .clone()
+        .filter(|pair| pair.as_rule() == Rule::grammar_rule)
+        .map(|pair| pair.into_inner().next().unwrap().as_span())
+        .collect();
+    let called_rules: Vec<_> = pairs
+        .clone()
+        .filter(|pair| pair.as_rule() == Rule::grammar_rule)
+        .flat_map(|pair| {
+            pair.into_inner()
+                .flatten()
+                .skip(1)
+                .filter(|pair| pair.as_rule() == Rule::identifier)
+                .map(|pair| pair.as_span())
+        })
+        .collect();
+
+    let mut errors = vec![];
+
+    errors.extend(validate_rust_keywords(&definitions, &rust_keywords));
+    errors.extend(validate_pest_keywords(&definitions, &pest_keywords));
+    errors.extend(validate_already_defined(&definitions));
+    errors.extend(validate_undefined(&definitions, &called_rules, &builtins));
+
+    if !errors.is_empty() {
+        return Err(errors);
+    }
+
+    let definitions: HashSet<_> = definitions.iter().map(|span| span.as_str()).collect();
+    let called_rules: HashSet<_> = called_rules.iter().map(|span| span.as_str()).collect();
+
+    let defaults = called_rules.difference(&definitions);
+
+    Ok(defaults.cloned().collect())
+}
+
+#[allow(clippy::implicit_hasher, clippy::ptr_arg)]
+pub fn validate_rust_keywords<'i>(
+    definitions: &Vec<Span<'i>>,
+    rust_keywords: &HashSet<&str>,
+) -> Vec<Error<Rule>> {
+    let mut errors = vec![];
+
+    for definition in definitions {
+        let name = definition.as_str();
+
+        if rust_keywords.contains(name) {
+            errors.push(Error::new_from_span(
+                ErrorVariant::CustomError {
+                    message: format!("{} is a rust keyword", name),
+                },
+                definition.clone(),
+            ))
+        }
+    }
+
+    errors
+}
+
+#[allow(clippy::implicit_hasher, clippy::ptr_arg)]
+pub fn validate_pest_keywords<'i>(
+    definitions: &Vec<Span<'i>>,
+    pest_keywords: &HashSet<&str>,
+) -> Vec<Error<Rule>> {
+    let mut errors = vec![];
+
+    for definition in definitions {
+        let name = definition.as_str();
+
+        if pest_keywords.contains(name) {
+            errors.push(Error::new_from_span(
+                ErrorVariant::CustomError {
+                    message: format!("{} is a pest keyword", name),
+                },
+                definition.clone(),
+            ))
+        }
+    }
+
+    errors
+}
+
+#[allow(clippy::ptr_arg)]
+pub fn validate_already_defined<'i>(definitions: &Vec<Span<'i>>) -> Vec<Error<Rule>> {
+    let mut errors = vec![];
+    let mut defined = HashSet::new();
+
+    for definition in definitions {
+        let name = definition.as_str();
+
+        if defined.contains(&name) {
+            errors.push(Error::new_from_span(
+                ErrorVariant::CustomError {
+                    message: format!("rule {} already defined", name),
+                },
+                definition.clone(),
+            ))
+        } else {
+            defined.insert(name);
+        }
+    }
+
+    errors
+}
+
+#[allow(clippy::implicit_hasher, clippy::ptr_arg)]
+pub fn validate_undefined<'i>(
+    definitions: &Vec<Span<'i>>,
+    called_rules: &Vec<Span<'i>>,
+    builtins: &HashSet<&str>,
+) -> Vec<Error<Rule>> {
+    let mut errors = vec![];
+    let definitions: HashSet<_> = definitions.iter().map(|span| span.as_str()).collect();
+
+    for rule in called_rules {
+        let name = rule.as_str();
+
+        if !definitions.contains(name) && !builtins.contains(name) {
+            errors.push(Error::new_from_span(
+                ErrorVariant::CustomError {
+                    message: format!("rule {} is undefined", name),
+                },
+                rule.clone(),
+            ))
+        }
+    }
+
+    errors
+}
+
+#[allow(clippy::ptr_arg)]
+pub fn validate_ast<'a, 'i: 'a>(rules: &'a Vec<ParserRule<'i>>) -> Vec<Error<Rule>> {
+    let mut errors = vec![];
+
+    errors.extend(validate_repetition(rules));
+    errors.extend(validate_choices(rules));
+    errors.extend(validate_whitespace_comment(rules));
+    errors.extend(validate_left_recursion(rules));
+
+    errors.sort_by_key(|error| match error.location {
+        InputLocation::Span(span) => span,
+        _ => unreachable!(),
+    });
+
+    errors
+}
+
+fn is_non_progressing<'i>(
+    expr: &ParserExpr<'i>,
+    rules: &HashMap<String, &ParserNode<'i>>,
+    trace: &mut Vec<String>,
+) -> bool {
+    match *expr {
+        ParserExpr::Str(ref string) => string == "",
+        ParserExpr::Ident(ref ident) => {
+            if ident == "soi" || ident == "eoi" {
+                return true;
+            }
+
+            if !trace.contains(ident) {
+                if let Some(node) = rules.get(ident) {
+                    trace.push(ident.clone());
+                    let result = is_non_progressing(&node.expr, rules, trace);
+                    trace.pop().unwrap();
+
+                    return result;
+                }
+            }
+
+            false
+        }
+        ParserExpr::PosPred(_) => true,
+        ParserExpr::NegPred(_) => true,
+        ParserExpr::Seq(ref lhs, ref rhs) => {
+            is_non_progressing(&lhs.expr, rules, trace)
+                && is_non_progressing(&rhs.expr, rules, trace)
+        }
+        ParserExpr::Choice(ref lhs, ref rhs) => {
+            is_non_progressing(&lhs.expr, rules, trace)
+                || is_non_progressing(&rhs.expr, rules, trace)
+        }
+        _ => false,
+    }
+}
+
+fn is_non_failing<'i>(
+    expr: &ParserExpr<'i>,
+    rules: &HashMap<String, &ParserNode<'i>>,
+    trace: &mut Vec<String>,
+) -> bool {
+    match *expr {
+        ParserExpr::Str(ref string) => string == "",
+        ParserExpr::Ident(ref ident) => {
+            if !trace.contains(ident) {
+                if let Some(node) = rules.get(ident) {
+                    trace.push(ident.clone());
+                    let result = is_non_failing(&node.expr, rules, trace);
+                    trace.pop().unwrap();
+
+                    return result;
+                }
+            }
+
+            false
+        }
+        ParserExpr::Opt(_) => true,
+        ParserExpr::Rep(_) => true,
+        ParserExpr::Seq(ref lhs, ref rhs) => {
+            is_non_failing(&lhs.expr, rules, trace) && is_non_failing(&rhs.expr, rules, trace)
+        }
+        ParserExpr::Choice(ref lhs, ref rhs) => {
+            is_non_failing(&lhs.expr, rules, trace) || is_non_failing(&rhs.expr, rules, trace)
+        }
+        _ => false,
+    }
+}
+
+fn validate_repetition<'a, 'i: 'a>(rules: &'a [ParserRule<'i>]) -> Vec<Error<Rule>> {
+    let mut result = vec![];
+    let map = to_hash_map(rules);
+
+    for rule in rules {
+        let mut errors = rule.node
+            .clone()
+            .filter_map_top_down(|node| match node.expr {
+                ParserExpr::Rep(ref other)
+                | ParserExpr::RepOnce(ref other)
+                | ParserExpr::RepMin(ref other, _) => {
+                    if is_non_failing(&other.expr, &map, &mut vec![]) {
+                        Some(Error::new_from_span(
+                            ErrorVariant::CustomError {
+                                message:
+                                    "expression inside repetition cannot fail and will repeat \
+                                     infinitely"
+                                        .to_owned()
+                            },
+                            node.span.clone()
+                        ))
+                    } else if is_non_progressing(&other.expr, &map, &mut vec![]) {
+                        Some(Error::new_from_span(
+                            ErrorVariant::CustomError {
+                                message:
+                                    "expression inside repetition is non-progressing and will repeat \
+                                     infinitely"
+                                        .to_owned(),
+                            },
+                            node.span.clone()
+                        ))
+                    } else {
+                        None
+                    }
+                }
+                _ => None
+            });
+
+        result.append(&mut errors);
+    }
+
+    result
+}
+
+fn validate_choices<'a, 'i: 'a>(rules: &'a [ParserRule<'i>]) -> Vec<Error<Rule>> {
+    let mut result = vec![];
+    let map = to_hash_map(rules);
+
+    for rule in rules {
+        let mut errors = rule
+            .node
+            .clone()
+            .filter_map_top_down(|node| match node.expr {
+                ParserExpr::Choice(ref lhs, _) => {
+                    let node = match lhs.expr {
+                        ParserExpr::Choice(_, ref rhs) => rhs,
+                        _ => lhs,
+                    };
+
+                    if is_non_failing(&node.expr, &map, &mut vec![]) {
+                        Some(Error::new_from_span(
+                            ErrorVariant::CustomError {
+                                message:
+                                    "expression cannot fail; following choices cannot be reached"
+                                        .to_owned(),
+                            },
+                            node.span.clone(),
+                        ))
+                    } else {
+                        None
+                    }
+                }
+                _ => None,
+            });
+
+        result.append(&mut errors);
+    }
+
+    result
+}
+
+fn validate_whitespace_comment<'a, 'i: 'a>(rules: &'a [ParserRule<'i>]) -> Vec<Error<Rule>> {
+    let map = to_hash_map(rules);
+
+    rules
+        .iter()
+        .filter_map(|rule| {
+            if rule.name == "WHITESPACE" || rule.name == "COMMENT" {
+                if is_non_failing(&rule.node.expr, &map, &mut vec![]) {
+                    Some(Error::new_from_span(
+                        ErrorVariant::CustomError {
+                            message: format!(
+                                "{} cannot fail and will repeat infinitely",
+                                &rule.name
+                            ),
+                        },
+                        rule.node.span.clone(),
+                    ))
+                } else if is_non_progressing(&rule.node.expr, &map, &mut vec![]) {
+                    Some(Error::new_from_span(
+                        ErrorVariant::CustomError {
+                            message: format!(
+                                "{} is non-progressing and will repeat infinitely",
+                                &rule.name
+                            ),
+                        },
+                        rule.node.span.clone(),
+                    ))
+                } else {
+                    None
+                }
+            } else {
+                None
+            }
+        })
+        .collect()
+}
+
+fn validate_left_recursion<'a, 'i: 'a>(rules: &'a [ParserRule<'i>]) -> Vec<Error<Rule>> {
+    left_recursion(to_hash_map(rules))
+}
+
+fn to_hash_map<'a, 'i: 'a>(rules: &'a [ParserRule<'i>]) -> HashMap<String, &'a ParserNode<'i>> {
+    rules.iter().map(|r| (r.name.clone(), &r.node)).collect()
+}
+
+#[allow(clippy::needless_pass_by_value)]
+fn left_recursion<'a, 'i: 'a>(rules: HashMap<String, &'a ParserNode<'i>>) -> Vec<Error<Rule>> {
+    fn check_expr<'a, 'i: 'a>(
+        node: &'a ParserNode<'i>,
+        rules: &'a HashMap<String, &ParserNode<'i>>,
+        trace: &mut Vec<String>,
+    ) -> Option<Error<Rule>> {
+        match node.expr.clone() {
+            ParserExpr::Ident(other) => {
+                if trace[0] == other {
+                    trace.push(other);
+                    let chain = trace
+                        .iter()
+                        .map(|ident| ident.as_ref())
+                        .collect::<Vec<_>>()
+                        .join(" -> ");
+
+                    return Some(Error::new_from_span(
+                        ErrorVariant::CustomError {
+                            message: format!(
+                                "rule {} is left-recursive ({}); pest::prec_climber might be useful \
+                                 in this case",
+                                node.span.as_str(),
+                                chain
+                            )
+                        },
+                        node.span.clone()
+                    ));
+                }
+
+                if !trace.contains(&other) {
+                    if let Some(node) = rules.get(&other) {
+                        trace.push(other);
+                        let result = check_expr(node, rules, trace);
+                        trace.pop().unwrap();
+
+                        return result;
+                    }
+                }
+
+                None
+            }
+            ParserExpr::Seq(ref lhs, ref rhs) => {
+                if is_non_failing(&lhs.expr, rules, &mut vec![trace.last().unwrap().clone()]) {
+                    check_expr(rhs, rules, trace)
+                } else {
+                    check_expr(lhs, rules, trace)
+                }
+            }
+            ParserExpr::Choice(ref lhs, ref rhs) => {
+                check_expr(&lhs, rules, trace).or_else(|| check_expr(&rhs, rules, trace))
+            }
+            ParserExpr::Rep(ref node) => check_expr(&node, rules, trace),
+            ParserExpr::RepOnce(ref node) => check_expr(&node, rules, trace),
+            ParserExpr::Opt(ref node) => check_expr(&node, rules, trace),
+            ParserExpr::PosPred(ref node) => check_expr(&node, rules, trace),
+            ParserExpr::NegPred(ref node) => check_expr(&node, rules, trace),
+            ParserExpr::Push(ref node) => check_expr(&node, rules, trace),
+            _ => None,
+        }
+    }
+
+    let mut errors = vec![];
+
+    for (ref name, ref node) in &rules {
+        let name = (*name).clone();
+
+        if let Some(error) = check_expr(node, &rules, &mut vec![name]) {
+            errors.push(error);
+        }
+    }
+
+    errors
+}
+
+#[cfg(test)]
+mod tests {
+    use super::super::parser::{consume_rules, PestParser};
+    use super::super::unwrap_or_report;
+    use super::*;
+    use pest::Parser;
+
+    #[test]
+    #[should_panic(expected = "grammar error
+
+ --> 1:1
+  |
+1 | let = { \"a\" }
+  | ^-^
+  |
+  = let is a rust keyword")]
+    fn rust_keyword() {
+        let input = "let = { \"a\" }";
+        unwrap_or_report(validate_pairs(
+            PestParser::parse(Rule::grammar_rules, input).unwrap(),
+        ));
+    }
+
+    #[test]
+    #[should_panic(expected = "grammar error
+
+ --> 1:1
+  |
+1 | ANY = { \"a\" }
+  | ^-^
+  |
+  = ANY is a pest keyword")]
+    fn pest_keyword() {
+        let input = "ANY = { \"a\" }";
+        unwrap_or_report(validate_pairs(
+            PestParser::parse(Rule::grammar_rules, input).unwrap(),
+        ));
+    }
+
+    #[test]
+    #[should_panic(expected = "grammar error
+
+ --> 1:13
+  |
+1 | a = { \"a\" } a = { \"a\" }
+  |             ^
+  |
+  = rule a already defined")]
+    fn already_defined() {
+        let input = "a = { \"a\" } a = { \"a\" }";
+        unwrap_or_report(validate_pairs(
+            PestParser::parse(Rule::grammar_rules, input).unwrap(),
+        ));
+    }
+
+    #[test]
+    #[should_panic(expected = "grammar error
+
+ --> 1:7
+  |
+1 | a = { b }
+  |       ^
+  |
+  = rule b is undefined")]
+    fn undefined() {
+        let input = "a = { b }";
+        unwrap_or_report(validate_pairs(
+            PestParser::parse(Rule::grammar_rules, input).unwrap(),
+        ));
+    }
+
+    #[test]
+    fn valid_recursion() {
+        let input = "a = { \"\" ~ \"a\"? ~ \"a\"* ~ (\"a\" | \"b\") ~ a }";
+        unwrap_or_report(consume_rules(
+            PestParser::parse(Rule::grammar_rules, input).unwrap(),
+        ));
+    }
+
+    #[test]
+    #[should_panic(expected = "grammar error
+
+ --> 1:16
+  |
+1 | WHITESPACE = { \"\" }
+  |                ^^
+  |
+  = WHITESPACE cannot fail and will repeat infinitely")]
+    fn non_failing_whitespace() {
+        let input = "WHITESPACE = { \"\" }";
+        unwrap_or_report(consume_rules(
+            PestParser::parse(Rule::grammar_rules, input).unwrap(),
+        ));
+    }
+
+    #[test]
+    #[should_panic(expected = "grammar error
+
+ --> 1:13
+  |
+1 | COMMENT = { soi }
+  |             ^-^
+  |
+  = COMMENT is non-progressing and will repeat infinitely")]
+    fn non_progressing_comment() {
+        let input = "COMMENT = { soi }";
+        unwrap_or_report(consume_rules(
+            PestParser::parse(Rule::grammar_rules, input).unwrap(),
+        ));
+    }
+
+    #[test]
+    #[should_panic(expected = "grammar error
+
+ --> 1:7
+  |
+1 | a = { (\"\")* }
+  |       ^---^
+  |
+  = expression inside repetition cannot fail and will repeat infinitely")]
+    fn non_failing_repetition() {
+        let input = "a = { (\"\")* }";
+        unwrap_or_report(consume_rules(
+            PestParser::parse(Rule::grammar_rules, input).unwrap(),
+        ));
+    }
+
+    #[test]
+    #[should_panic(expected = "grammar error
+
+ --> 1:18
+  |
+1 | a = { \"\" } b = { a* }
+  |                  ^^
+  |
+  = expression inside repetition cannot fail and will repeat infinitely")]
+    fn indirect_non_failing_repetition() {
+        let input = "a = { \"\" } b = { a* }";
+        unwrap_or_report(consume_rules(
+            PestParser::parse(Rule::grammar_rules, input).unwrap(),
+        ));
+    }
+
+    #[test]
+    #[should_panic(expected = "grammar error
+
+ --> 1:20
+  |
+1 | a = { \"a\" ~ (\"b\" ~ (\"\")*) }
+  |                    ^---^
+  |
+  = expression inside repetition cannot fail and will repeat infinitely")]
+    fn deep_non_failing_repetition() {
+        let input = "a = { \"a\" ~ (\"b\" ~ (\"\")*) }";
+        unwrap_or_report(consume_rules(
+            PestParser::parse(Rule::grammar_rules, input).unwrap(),
+        ));
+    }
+
+    #[test]
+    #[should_panic(expected = "grammar error
+
+ --> 1:7
+  |
+1 | a = { (\"\" ~ &\"a\" ~ !\"a\" ~ (soi | eoi))* }
+  |       ^-------------------------------^
+  |
+  = expression inside repetition is non-progressing and will repeat infinitely")]
+    fn non_progressing_repetition() {
+        let input = "a = { (\"\" ~ &\"a\" ~ !\"a\" ~ (soi | eoi))* }";
+        unwrap_or_report(consume_rules(
+            PestParser::parse(Rule::grammar_rules, input).unwrap(),
+        ));
+    }
+
+    #[test]
+    #[should_panic(expected = "grammar error
+
+ --> 1:20
+  |
+1 | a = { !\"a\" } b = { a* }
+  |                    ^^
+  |
+  = expression inside repetition is non-progressing and will repeat infinitely")]
+    fn indirect_non_progressing_repetition() {
+        let input = "a = { !\"a\" } b = { a* }";
+        unwrap_or_report(consume_rules(
+            PestParser::parse(Rule::grammar_rules, input).unwrap(),
+        ));
+    }
+
+    #[test]
+    #[should_panic(expected = "grammar error
+
+ --> 1:7
+  |
+1 | a = { a }
+  |       ^
+  |
+  = rule a is left-recursive (a -> a); pest::prec_climber might be useful in this case")]
+    fn simple_left_recursion() {
+        let input = "a = { a }";
+        unwrap_or_report(consume_rules(
+            PestParser::parse(Rule::grammar_rules, input).unwrap(),
+        ));
+    }
+
+    #[test]
+    #[should_panic(expected = "grammar error
+
+ --> 1:7
+  |
+1 | a = { b } b = { a }
+  |       ^
+  |
+  = rule b is left-recursive (b -> a -> b); pest::prec_climber might be useful in this case
+
+ --> 1:17
+  |
+1 | a = { b } b = { a }
+  |                 ^
+  |
+  = rule a is left-recursive (a -> b -> a); pest::prec_climber might be useful in this case")]
+    fn indirect_left_recursion() {
+        let input = "a = { b } b = { a }";
+        unwrap_or_report(consume_rules(
+            PestParser::parse(Rule::grammar_rules, input).unwrap(),
+        ));
+    }
+
+    #[test]
+    #[should_panic(expected = "grammar error
+
+ --> 1:39
+  |
+1 | a = { \"\" ~ \"a\"? ~ \"a\"* ~ (\"a\" | \"\") ~ a }
+  |                                       ^
+  |
+  = rule a is left-recursive (a -> a); pest::prec_climber might be useful in this case")]
+    fn non_failing_left_recursion() {
+        let input = "a = { \"\" ~ \"a\"? ~ \"a\"* ~ (\"a\" | \"\") ~ a }";
+        unwrap_or_report(consume_rules(
+            PestParser::parse(Rule::grammar_rules, input).unwrap(),
+        ));
+    }
+
+    #[test]
+    #[should_panic(expected = "grammar error
+
+ --> 1:13
+  |
+1 | a = { \"a\" | a }
+  |             ^
+  |
+  = rule a is left-recursive (a -> a); pest::prec_climber might be useful in this case")]
+    fn non_primary_choice_left_recursion() {
+        let input = "a = { \"a\" | a }";
+        unwrap_or_report(consume_rules(
+            PestParser::parse(Rule::grammar_rules, input).unwrap(),
+        ));
+    }
+
+    #[test]
+    #[should_panic(expected = "grammar error
+
+ --> 1:7
+  |
+1 | a = { \"a\"* | \"a\" | \"b\" }
+  |       ^--^
+  |
+  = expression cannot fail; following choices cannot be reached")]
+    fn lhs_non_failing_choice() {
+        let input = "a = { \"a\"* | \"a\" | \"b\" }";
+        unwrap_or_report(consume_rules(
+            PestParser::parse(Rule::grammar_rules, input).unwrap(),
+        ));
+    }
+
+    #[test]
+    #[should_panic(expected = "grammar error
+
+ --> 1:13
+  |
+1 | a = { \"a\" | \"a\"* | \"b\" }
+  |             ^--^
+  |
+  = expression cannot fail; following choices cannot be reached")]
+    fn lhs_non_failing_choice_middle() {
+        let input = "a = { \"a\" | \"a\"* | \"b\" }";
+        unwrap_or_report(consume_rules(
+            PestParser::parse(Rule::grammar_rules, input).unwrap(),
+        ));
+    }
+
+    #[test]
+    #[should_panic(expected = "grammar error
+
+ --> 1:7
+  |
+1 | a = { b | \"a\" } b = { \"b\"* | \"c\" }
+  |       ^
+  |
+  = expression cannot fail; following choices cannot be reached
+
+ --> 1:23
+  |
+1 | a = { b | \"a\" } b = { \"b\"* | \"c\" }
+  |                       ^--^
+  |
+  = expression cannot fail; following choices cannot be reached")]
+    fn lhs_non_failing_nested_choices() {
+        let input = "a = { b | \"a\" } b = { \"b\"* | \"c\" }";
+        unwrap_or_report(consume_rules(
+            PestParser::parse(Rule::grammar_rules, input).unwrap(),
+        ));
+    }
+
+    #[test]
+    fn skip_can_be_defined() {
+        let input = "skip = { \"\" }";
+        unwrap_or_report(consume_rules(
+            PestParser::parse(Rule::grammar_rules, input).unwrap(),
+        ));
+    }
+}