| extern crate nom; |
| |
| |
| use nom::{ |
| IResult, |
| branch::alt, |
| combinator::map_res, |
| character::complete::char, |
| bytes::complete::tag, |
| character::complete::{digit1 as digit, space0 as space}, |
| multi::fold_many0, |
| sequence::{delimited, pair} |
| }; |
| |
| // Parser definition |
| |
| use std::str::FromStr; |
| |
| // We parse any expr surrounded by parens, ignoring all whitespaces around those |
| fn parens(i: &str) -> IResult<&str, i64> { |
| delimited( |
| space, |
| delimited( |
| tag("("), |
| expr, |
| tag(")") |
| ), |
| space |
| )(i) |
| } |
| |
| // We transform an integer string into a i64, ignoring surrounding whitespaces |
| // We look for a digit suite, and try to convert it. |
| // If either str::from_utf8 or FromStr::from_str fail, |
| // we fallback to the parens parser defined above |
| fn factor(i: &str) -> IResult<&str, i64> { |
| alt(( |
| map_res(delimited(space, digit, space), FromStr::from_str), |
| parens |
| ))(i) |
| } |
| |
| // We read an initial factor and for each time we find |
| // a * or / operator followed by another factor, we do |
| // the math by folding everything |
| fn term(i: &str) -> IResult<&str, i64> { |
| let (i, init) = factor(i)?; |
| |
| fold_many0( |
| pair(alt((char('*'), char('/'))), factor), |
| init, |
| |acc, (op, val): (char, i64)| { |
| if op == '*' { acc * val } else { acc / val } |
| } |
| )(i) |
| } |
| |
| fn expr(i: &str) -> IResult<&str, i64> { |
| let (i, init) = term(i)?; |
| |
| fold_many0( |
| pair(alt((char('+'), char('-'))), term), |
| init, |
| |acc, (op, val): (char, i64)| { |
| if op == '+' { acc + val } else { acc - val } |
| } |
| )(i) |
| } |
| |
| #[test] |
| fn factor_test() { |
| assert_eq!(factor("3"), Ok(("", 3))); |
| assert_eq!(factor(" 12"), Ok(("", 12))); |
| assert_eq!(factor("537 "), Ok(("", 537))); |
| assert_eq!(factor(" 24 "), Ok(("", 24))); |
| } |
| |
| #[test] |
| fn term_test() { |
| assert_eq!(term(" 12 *2 / 3"), Ok(("", 8))); |
| assert_eq!( |
| term(" 2* 3 *2 *2 / 3"), |
| Ok(("", 8)) |
| ); |
| assert_eq!(term(" 48 / 3/2"), Ok(("", 8))); |
| } |
| |
| #[test] |
| fn expr_test() { |
| assert_eq!(expr(" 1 + 2 "), Ok(("", 3))); |
| assert_eq!( |
| expr(" 12 + 6 - 4+ 3"), |
| Ok(("", 17)) |
| ); |
| assert_eq!(expr(" 1 + 2*3 + 4"), Ok(("", 11))); |
| } |
| |
| #[test] |
| fn parens_test() { |
| assert_eq!(expr(" ( 2 )"), Ok(("", 2))); |
| assert_eq!( |
| expr(" 2* ( 3 + 4 ) "), |
| Ok(("", 14)) |
| ); |
| assert_eq!( |
| expr(" 2*2 / ( 5 - 1) + 3"), |
| Ok(("", 4)) |
| ); |
| } |