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android / platform / external / antlr / b7f974f39180d46da516fb24eb2b1ca67d56089c / . / tool / src / main / java / org / antlr / analysis / DFAState.java
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/*
* [The "BSD license"]
* Copyright (c) 2010 Terence Parr
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. The name of the author may not be used to endorse or promote products
* derived from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
package org.antlr.analysis;
import org.antlr.misc.IntSet;
import org.antlr.misc.MultiMap;
import org.antlr.misc.OrderedHashSet;
import org.antlr.misc.Utils;
import org.antlr.tool.Grammar;
import java.util.*;
/** A DFA state represents a set of possible NFA configurations.
* As Aho, Sethi, Ullman p. 117 says "The DFA uses its state
* to keep track of all possible states the NFA can be in after
* reading each input symbol. That is to say, after reading
* input a1a2..an, the DFA is in a state that represents the
* subset T of the states of the NFA that are reachable from the
* NFA's start state along some path labeled a1a2..an."
* In conventional NFA→DFA conversion, therefore, the subset T
* would be a bitset representing the set of states the
* NFA could be in. We need to track the alt predicted by each
* state as well, however. More importantly, we need to maintain
* a stack of states, tracking the closure operations as they
* jump from rule to rule, emulating rule invocations (method calls).
* Recall that NFAs do not normally have a stack like a pushdown-machine
* so I have to add one to simulate the proper lookahead sequences for
* the underlying LL grammar from which the NFA was derived.
*
* I use a list of NFAConfiguration objects. An NFAConfiguration
* is both a state (ala normal conversion) and an NFAContext describing
* the chain of rules (if any) followed to arrive at that state. There
* is also the semantic context, which is the "set" of predicates found
* on the path to this configuration.
*
* A DFA state may have multiple references to a particular state,
* but with different NFAContexts (with same or different alts)
* meaning that state was reached via a different set of rule invocations.
*/
public class DFAState extends State {
public static final int INITIAL_NUM_TRANSITIONS = 4;
public static final int PREDICTED_ALT_UNSET = NFA.INVALID_ALT_NUMBER-1;
/** We are part of what DFA? Use this ref to get access to the
* context trees for an alt.
*/
public DFA dfa;
/** Track the transitions emanating from this DFA state. The List
* elements are Transition objects.
*/
protected List<Transition> transitions =
new ArrayList<Transition>(INITIAL_NUM_TRANSITIONS);
/** When doing an acyclic DFA, this is the number of lookahead symbols
* consumed to reach this state. This value may be nonzero for most
* dfa states, but it is only a valid value if the user has specified
* a max fixed lookahead.
*/
protected int k;
/** The NFA&rarr;DFA algorithm may terminate leaving some states
* without a path to an accept state, implying that upon certain
* input, the decision is not deterministic--no decision about
* predicting a unique alternative can be made. Recall that an
* accept state is one in which a unique alternative is predicted.
*/
protected int acceptStateReachable = DFA.REACHABLE_UNKNOWN;
/** Rather than recheck every NFA configuration in a DFA state (after
* resolving) in findNewDFAStatesAndAddDFATransitions just check
* this boolean. Saves a linear walk perhaps DFA state creation.
* Every little bit helps.
*/
protected boolean resolvedWithPredicates = false;
/** If a closure operation finds that we tried to invoke the same
* rule too many times (stack would grow beyond a threshold), it
* marks the state has aborted and notifies the DecisionProbe.
*/
public boolean abortedDueToRecursionOverflow = false;
/** If we detect recursion on more than one alt, decision is non-LL(*),
* but try to isolate it to only those states whose closure operations
* detect recursion. There may be other alts that are cool:
*
* a : recur '.'
* | recur ';'
* | X Y // LL(2) decision; don't abort and use k=1 plus backtracking
* | X Z
* ;
*
* 12/13/2007: Actually this has caused problems. If k=*, must terminate
* and throw out entire DFA; retry with k=1. Since recursive, do not
* attempt more closure ops as it may take forever. Exception thrown
* now and we simply report the problem. If synpreds exist, I'll retry
* with k=1.
*/
protected boolean abortedDueToMultipleRecursiveAlts = false;
/** Build up the hash code for this state as NFA configurations
* are added as it's monotonically increasing list of configurations.
*/
protected int cachedHashCode;
protected int cachedUniquelyPredicatedAlt = PREDICTED_ALT_UNSET;
public int minAltInConfigurations=Integer.MAX_VALUE;
public boolean atLeastOneConfigurationHasAPredicate = false;
/** The set of NFA configurations (state,alt,context) for this DFA state */
public OrderedHashSet<NFAConfiguration> nfaConfigurations =
new OrderedHashSet<NFAConfiguration>();
public List<NFAConfiguration> configurationsWithLabeledEdges =
new ArrayList<NFAConfiguration>();
/** Used to prevent the closure operation from looping to itself and
* hence looping forever. Sensitive to the NFA state, the alt, and
* the stack context. This just the nfa config set because we want to
* prevent closures only on states contributed by closure not reach
* operations.
*
* Two configurations identical including semantic context are
* considered the same closure computation. @see NFAToDFAConverter.closureBusy().
*/
protected Set<NFAConfiguration> closureBusy = new HashSet<NFAConfiguration>();
/** As this state is constructed (i.e., as NFA states are added), we
* can easily check for non-epsilon transitions because the only
* transition that could be a valid label is transition(0). When we
* process this node eventually, we'll have to walk all states looking
* for all possible transitions. That is of the order: size(label space)
* times size(nfa states), which can be pretty damn big. It's better
* to simply track possible labels.
*/
protected OrderedHashSet<Label> reachableLabels;
public DFAState(DFA dfa) {
this.dfa = dfa;
}
public void reset() {
//nfaConfigurations = null; // getGatedPredicatesInNFAConfigurations needs
configurationsWithLabeledEdges = null;
closureBusy = null;
reachableLabels = null;
}
@Override
public Transition transition(int i) {
return transitions.get(i);
}
@Override
public int getNumberOfTransitions() {
return transitions.size();
}
@Override
public void addTransition(Transition t) {
transitions.add(t);
}
/** Add a transition from this state to target with label. Return
* the transition number from 0..n-1.
*/
public int addTransition(DFAState target, Label label) {
transitions.add( new Transition(label, target) );
return transitions.size()-1;
}
public Transition getTransition(int trans) {
return transitions.get(trans);
}
public void removeTransition(int trans) {
transitions.remove(trans);
}
/** Add an NFA configuration to this DFA node. Add uniquely
* an NFA state/alt/syntactic&amp;semantic context (chain of invoking state(s)
* and semantic predicate contexts).
*
* I don't see how there could be two configurations with same
* state|alt|synCtx and different semantic contexts because the
* semantic contexts are computed along the path to a particular state
* so those two configurations would have to have the same predicate.
* Nonetheless, the addition of configurations is unique on all
* configuration info. I guess I'm saying that syntactic context
* implies semantic context as the latter is computed according to the
* former.
*
* As we add configurations to this DFA state, track the set of all possible
* transition labels so we can simply walk it later rather than doing a
* loop over all possible labels in the NFA.
*/
public void addNFAConfiguration(NFAState state, NFAConfiguration c) {
if ( nfaConfigurations.contains(c) ) {
return;
}
nfaConfigurations.add(c);
// track min alt rather than compute later
if ( c.alt < minAltInConfigurations ) {
minAltInConfigurations = c.alt;
}
if ( c.semanticContext!=SemanticContext.EMPTY_SEMANTIC_CONTEXT ) {
atLeastOneConfigurationHasAPredicate = true;
}
// update hashCode; for some reason using context.hashCode() also
// makes the GC take like 70% of the CPU and is slow!
cachedHashCode += c.state + c.alt;
// update reachableLabels
// We're adding an NFA state; check to see if it has a non-epsilon edge
if ( state.transition[0] != null ) {
Label label = state.transition[0].label;
if ( !(label.isEpsilon()||label.isSemanticPredicate()) ) {
// this NFA state has a non-epsilon edge, track for fast
// walking later when we do reach on this DFA state we're
// building.
configurationsWithLabeledEdges.add(c);
if ( state.transition[1] ==null ) {
// later we can check this to ignore o-A->o states in closure
c.singleAtomTransitionEmanating = true;
}
addReachableLabel(label);
}
}
}
public NFAConfiguration addNFAConfiguration(NFAState state,
int alt,
NFAContext context,
SemanticContext semanticContext)
{
NFAConfiguration c = new NFAConfiguration(state.stateNumber,
alt,
context,
semanticContext);
addNFAConfiguration(state, c);
return c;
}
/** Add label uniquely and disjointly; intersection with
* another set or int/char forces breaking up the set(s).
*
* Example, if reachable list of labels is [a..z, {k,9}, 0..9],
* the disjoint list will be [{a..j,l..z}, k, 9, 0..8].
*
* As we add NFA configurations to a DFA state, we might as well track
* the set of all possible transition labels to make the DFA conversion
* more efficient. W/o the reachable labels, we'd need to check the
* whole vocabulary space (could be 0..\uFFFF)! The problem is that
* labels can be sets, which may overlap with int labels or other sets.
* As we need a deterministic set of transitions from any
* state in the DFA, we must make the reachable labels set disjoint.
* This operation amounts to finding the character classes for this
* DFA state whereas with tools like flex, that need to generate a
* homogeneous DFA, must compute char classes across all states.
* We are going to generate DFAs with heterogeneous states so we
* only care that the set of transitions out of a single state are
* unique. :)
*
* The idea for adding a new set, t, is to look for overlap with the
* elements of existing list s. Upon overlap, replace
* existing set s[i] with two new disjoint sets, s[i]-t and s[i]&amp;t.
* (if s[i]-t is nil, don't add). The remainder is t-s[i], which is
* what you want to add to the set minus what was already there. The
* remainder must then be compared against the i+1..n elements in s
* looking for another collision. Each collision results in a smaller
* and smaller remainder. Stop when you run out of s elements or
* remainder goes to nil. If remainder is non nil when you run out of
* s elements, then add remainder to the end.
*
* Single element labels are treated as sets to make the code uniform.
*/
protected void addReachableLabel(Label label) {
if ( reachableLabels==null ) {
reachableLabels = new OrderedHashSet<Label>();
}
/*
System.out.println("addReachableLabel to state "+dfa.decisionNumber+"."+stateNumber+": "+label.getSet().toString(dfa.nfa.grammar));
System.out.println("start of add to state "+dfa.decisionNumber+"."+stateNumber+": " +
"reachableLabels="+reachableLabels.toString());
*/
if ( reachableLabels.contains(label) ) { // exact label present
return;
}
IntSet t = label.getSet();
IntSet remainder = t; // remainder starts out as whole set to add
int n = reachableLabels.size(); // only look at initial elements
// walk the existing list looking for the collision
for (int i=0; i<n; i++) {
Label rl = reachableLabels.get(i);
/*
System.out.println("comparing ["+i+"]: "+label.toString(dfa.nfa.grammar)+" & "+
rl.toString(dfa.nfa.grammar)+"="+
intersection.toString(dfa.nfa.grammar));
*/
if ( !Label.intersect(label, rl) ) {
continue;
}
//System.out.println(label+" collides with "+rl);
// For any (s_i, t) with s_i&t!=nil replace with (s_i-t, s_i&t)
// (ignoring s_i-t if nil; don't put in list)
// Replace existing s_i with intersection since we
// know that will always be a non nil character class
IntSet s_i = rl.getSet();
IntSet intersection = s_i.and(t);
reachableLabels.set(i, new Label(intersection));
// Compute s_i-t to see what is in current set and not in incoming
IntSet existingMinusNewElements = s_i.subtract(t);
//System.out.println(s_i+"-"+t+"="+existingMinusNewElements);
if ( !existingMinusNewElements.isNil() ) {
// found a new character class, add to the end (doesn't affect
// outer loop duration due to n computation a priori.
Label newLabel = new Label(existingMinusNewElements);
reachableLabels.add(newLabel);
}
/*
System.out.println("after collision, " +
"reachableLabels="+reachableLabels.toString());
*/
// anything left to add to the reachableLabels?
remainder = t.subtract(s_i);
if ( remainder.isNil() ) {
break; // nothing left to add to set. done!
}
t = remainder;
}
if ( !remainder.isNil() ) {
/*
System.out.println("before add remainder to state "+dfa.decisionNumber+"."+stateNumber+": " +
"reachableLabels="+reachableLabels.toString());
System.out.println("remainder state "+dfa.decisionNumber+"."+stateNumber+": "+remainder.toString(dfa.nfa.grammar));
*/
Label newLabel = new Label(remainder);
reachableLabels.add(newLabel);
}
/*
System.out.println("#END of add to state "+dfa.decisionNumber+"."+stateNumber+": " +
"reachableLabels="+reachableLabels.toString());
*/
}
public OrderedHashSet<Label> getReachableLabels() {
return reachableLabels;
}
public void setNFAConfigurations(OrderedHashSet<NFAConfiguration> configs) {
this.nfaConfigurations = configs;
}
/** A decent hash for a DFA state is the sum of the NFA state/alt pairs.
* This is used when we add DFAState objects to the DFA.states Map and
* when we compare DFA states. Computed in addNFAConfiguration()
*/
@Override
public int hashCode() {
if ( cachedHashCode==0 ) {
// LL(1) algorithm doesn't use NFA configurations, which
// dynamically compute hashcode; must have something; use super
return super.hashCode();
}
return cachedHashCode;
}
/** Two DFAStates are equal if their NFA configuration sets are the
* same. This method is used to see if a DFA state already exists.
*
* Because the number of alternatives and number of NFA configurations are
* finite, there is a finite number of DFA states that can be processed.
* This is necessary to show that the algorithm terminates.
*
* Cannot test the DFA state numbers here because in DFA.addState we need
* to know if any other state exists that has this exact set of NFA
* configurations. The DFAState state number is irrelevant.
*/
@Override
public boolean equals(Object o) {
// compare set of NFA configurations in this set with other
DFAState other = (DFAState)o;
return this.nfaConfigurations.equals(other.nfaConfigurations);
}
/** Walk each configuration and if they are all the same alt, return
* that alt else return NFA.INVALID_ALT_NUMBER. Ignore resolved
* configurations, but don't ignore resolveWithPredicate configs
* because this state should not be an accept state. We need to add
* this to the work list and then have semantic predicate edges
* emanating from it.
*/
public int getUniquelyPredictedAlt() {
if ( cachedUniquelyPredicatedAlt!=PREDICTED_ALT_UNSET ) {
return cachedUniquelyPredicatedAlt;
}
int alt = NFA.INVALID_ALT_NUMBER;
int numConfigs = nfaConfigurations.size();
for (int i = 0; i < numConfigs; i++) {
NFAConfiguration configuration = nfaConfigurations.get(i);
// ignore anything we resolved; predicates will still result
// in transitions out of this state, so must count those
// configurations; i.e., don't ignore resolveWithPredicate configs
if ( configuration.resolved ) {
continue;
}
if ( alt==NFA.INVALID_ALT_NUMBER ) {
alt = configuration.alt; // found first nonresolved alt
}
else if ( configuration.alt!=alt ) {
return NFA.INVALID_ALT_NUMBER;
}
}
this.cachedUniquelyPredicatedAlt = alt;
return alt;
}
/** Return the uniquely mentioned alt from the NFA configurations;
* Ignore the resolved bit etc... Return INVALID_ALT_NUMBER
* if there is more than one alt mentioned.
*/
public int getUniqueAlt() {
int alt = NFA.INVALID_ALT_NUMBER;
int numConfigs = nfaConfigurations.size();
for (int i = 0; i < numConfigs; i++) {
NFAConfiguration configuration = nfaConfigurations.get(i);
if ( alt==NFA.INVALID_ALT_NUMBER ) {
alt = configuration.alt; // found first alt
}
else if ( configuration.alt!=alt ) {
return NFA.INVALID_ALT_NUMBER;
}
}
return alt;
}
/** When more than one alternative can match the same input, the first
* alternative is chosen to resolve the conflict. The other alts
* are "turned off" by setting the "resolved" flag in the NFA
* configurations. Return the set of disabled alternatives. For
*
* a : A | A | A ;
*
* this method returns {2,3} as disabled. This does not mean that
* the alternative is totally unreachable, it just means that for this
* DFA state, that alt is disabled. There may be other accept states
* for that alt.
*/
public Set<Integer> getDisabledAlternatives() {
Set<Integer> disabled = new LinkedHashSet<Integer>();
int numConfigs = nfaConfigurations.size();
for (int i = 0; i < numConfigs; i++) {
NFAConfiguration configuration = nfaConfigurations.get(i);
if ( configuration.resolved ) {
disabled.add(Utils.integer(configuration.alt));
}
}
return disabled;
}
protected Set<Integer> getNonDeterministicAlts() {
int user_k = dfa.getUserMaxLookahead();
if ( user_k>0 && user_k==k ) {
// if fixed lookahead, then more than 1 alt is a nondeterminism
// if we have hit the max lookahead
return getAltSet();
}
else if ( abortedDueToMultipleRecursiveAlts || abortedDueToRecursionOverflow ) {
// if we had to abort for non-LL(*) state assume all alts are a problem
return getAltSet();
}
else {
return getConflictingAlts();
}
}
/** Walk each NFA configuration in this DFA state looking for a conflict
* where (s|i|ctx) and (s|j|ctx) exist, indicating that state s with
* context conflicting ctx predicts alts i and j. Return an Integer set
* of the alternative numbers that conflict. Two contexts conflict if
* they are equal or one is a stack suffix of the other or one is
* the empty context.
*
* Use a hash table to record the lists of configs for each state
* as they are encountered. We need only consider states for which
* there is more than one configuration. The configurations' predicted
* alt must be different or must have different contexts to avoid a
* conflict.
*
* Don't report conflicts for DFA states that have conflicting Tokens
* rule NFA states; they will be resolved in favor of the first rule.
*/
protected Set<Integer> getConflictingAlts() {
// TODO this is called multiple times: cache result?
//System.out.println("getNondetAlts for DFA state "+stateNumber);
Set<Integer> nondeterministicAlts = new HashSet<Integer>();
// If only 1 NFA conf then no way it can be nondeterministic;
// save the overhead. There are many o-a->o NFA transitions
// and so we save a hash map and iterator creation for each
// state.
int numConfigs = nfaConfigurations.size();
if ( numConfigs <=1 ) {
return null;
}
// First get a list of configurations for each state.
// Most of the time, each state will have one associated configuration.
MultiMap<Integer, NFAConfiguration> stateToConfigListMap =
new MultiMap<Integer, NFAConfiguration>();
for (int i = 0; i < numConfigs; i++) {
NFAConfiguration configuration = nfaConfigurations.get(i);
Integer stateI = Utils.integer(configuration.state);
stateToConfigListMap.map(stateI, configuration);
}
// potential conflicts are states with > 1 configuration and diff alts
Set<Integer> states = stateToConfigListMap.keySet();
int numPotentialConflicts = 0;
for (Integer stateI : states) {
boolean thisStateHasPotentialProblem = false;
List<NFAConfiguration> configsForState = stateToConfigListMap.get(stateI);
int alt=0;
int numConfigsForState = configsForState.size();
for (int i = 0; i < numConfigsForState && numConfigsForState>1 ; i++) {
NFAConfiguration c = configsForState.get(i);
if ( alt==0 ) {
alt = c.alt;
}
else if ( c.alt!=alt ) {
/*
System.out.println("potential conflict in state "+stateI+
" configs: "+configsForState);
*/
// 11/28/2005: don't report closures that pinch back
// together in Tokens rule. We want to silently resolve
// to the first token definition ala lex/flex by ignoring
// these conflicts.
// Also this ensures that lexers look for more and more
// characters (longest match) before resorting to predicates.
// TestSemanticPredicates.testLexerMatchesLongestThenTestPred()
// for example would terminate at state s1 and test predicate
// meaning input "ab" would test preds to decide what to
// do but it should match rule C w/o testing preds.
if ( dfa.nfa.grammar.type!=Grammar.LEXER ||
!dfa.decisionNFAStartState.enclosingRule.name.equals(Grammar.ARTIFICIAL_TOKENS_RULENAME) )
{
numPotentialConflicts++;
thisStateHasPotentialProblem = true;
}
}
}
if ( !thisStateHasPotentialProblem ) {
// remove NFA state's configurations from
// further checking; no issues with it
// (can't remove as it's concurrent modification; set to null)
stateToConfigListMap.put(stateI, null);
}
}
// a fast check for potential issues; most states have none
if ( numPotentialConflicts==0 ) {
return null;
}
// we have a potential problem, so now go through config lists again
// looking for different alts (only states with potential issues
// are left in the states set). Now we will check context.
// For example, the list of configs for NFA state 3 in some DFA
// state might be:
// [3|2|[28 18 $], 3|1|[28 $], 3|1, 3|2]
// I want to create a map from context to alts looking for overlap:
// [28 18 $] -> 2
// [28 $] -> 1
// [$] -> 1,2
// Indeed a conflict exists as same state 3, same context [$], predicts
// alts 1 and 2.
// walk each state with potential conflicting configurations
for (Integer stateI : states) {
List<NFAConfiguration> configsForState = stateToConfigListMap.get(stateI);
// compare each configuration pair s, t to ensure:
// s.ctx different than t.ctx if s.alt != t.alt
int numConfigsForState = 0;
if ( configsForState!=null ) {
numConfigsForState = configsForState.size();
}
for (int i = 0; i < numConfigsForState; i++) {
NFAConfiguration s = configsForState.get(i);
for (int j = i+1; j < numConfigsForState; j++) {
NFAConfiguration t = configsForState.get(j);
// conflicts means s.ctx==t.ctx or s.ctx is a stack
// suffix of t.ctx or vice versa (if alts differ).
// Also a conflict if s.ctx or t.ctx is empty
if ( s.alt != t.alt && s.context.conflictsWith(t.context) ) {
nondeterministicAlts.add(Utils.integer(s.alt));
nondeterministicAlts.add(Utils.integer(t.alt));
}
}
}
}
if ( nondeterministicAlts.isEmpty() ) {
return null;
}
return nondeterministicAlts;
}
/** Get the set of all alts mentioned by all NFA configurations in this
* DFA state.
*/
public Set<Integer> getAltSet() {
int numConfigs = nfaConfigurations.size();
Set<Integer> alts = new HashSet<Integer>();
for (int i = 0; i < numConfigs; i++) {
NFAConfiguration configuration = nfaConfigurations.get(i);
alts.add(Utils.integer(configuration.alt));
}
if ( alts.isEmpty() ) {
return null;
}
return alts;
}
public Set<? extends SemanticContext> getGatedSyntacticPredicatesInNFAConfigurations() {
int numConfigs = nfaConfigurations.size();
Set<SemanticContext> synpreds = new HashSet<SemanticContext>();
for (int i = 0; i < numConfigs; i++) {
NFAConfiguration configuration = nfaConfigurations.get(i);
SemanticContext gatedPredExpr =
configuration.semanticContext.getGatedPredicateContext();
// if this is a manual syn pred (gated and syn pred), add
if ( gatedPredExpr!=null &&
configuration.semanticContext.isSyntacticPredicate() )
{
synpreds.add(configuration.semanticContext);
}
}
if ( synpreds.isEmpty() ) {
return null;
}
return synpreds;
}
/** For gated productions, we need an OR'd list of all predicates for the
* target of an edge so we can gate the edge based upon the predicates
* associated with taking that path (if any).
*
* For syntactic predicates, we only want to generate predicate
* evaluations as it transitions to an accept state; waste to
* do it earlier. So, only add gated preds derived from manually-
* specified syntactic predicates if this is an accept state.
*
* Also, since configurations w/o gated predicates are like true
* gated predicates, finding a configuration whose alt has no gated
* predicate implies we should evaluate the predicate to true. This
* means the whole edge has to be ungated. Consider:
*
* X : ('a' | {p}?=&gt; 'a')
* | 'a' 'b'
* ;
*
* Here, you 'a' gets you from s0 to s1 but you can't test p because
* plain 'a' is ok. It's also ok for starting alt 2. Hence, you can't
* test p. Even on the edge going to accept state for alt 1 of X, you
* can't test p. You can get to the same place with and w/o the context.
* Therefore, it is never ok to test p in this situation.
*
* TODO: cache this as it's called a lot; or at least set bit if &gt;1 present in state
*/
public SemanticContext getGatedPredicatesInNFAConfigurations() {
SemanticContext unionOfPredicatesFromAllAlts = null;
int numConfigs = nfaConfigurations.size();
for (int i = 0; i < numConfigs; i++) {
NFAConfiguration configuration = nfaConfigurations.get(i);
SemanticContext gatedPredExpr =
configuration.semanticContext.getGatedPredicateContext();
if ( gatedPredExpr==null ) {
// if we ever find a configuration w/o a gated predicate
// (even if it's a nongated predicate), we cannot gate
// the indident edges.
return null;
}
else if ( acceptState || !configuration.semanticContext.isSyntacticPredicate() ) {
// at this point we have a gated predicate and, due to elseif,
// we know it's an accept or not a syn pred. In this case,
// it's safe to add the gated predicate to the union. We
// only want to add syn preds if it's an accept state. Other
// gated preds can be used with edges leading to accept states.
if ( unionOfPredicatesFromAllAlts==null ) {
unionOfPredicatesFromAllAlts = gatedPredExpr;
}
else {
unionOfPredicatesFromAllAlts =
SemanticContext.or(unionOfPredicatesFromAllAlts,gatedPredExpr);
}
}
}
if ( unionOfPredicatesFromAllAlts instanceof SemanticContext.TruePredicate ) {
return null;
}
return unionOfPredicatesFromAllAlts;
}
/** Is an accept state reachable from this state? */
public int getAcceptStateReachable() {
return acceptStateReachable;
}
public void setAcceptStateReachable(int acceptStateReachable) {
this.acceptStateReachable = acceptStateReachable;
}
public boolean isResolvedWithPredicates() {
return resolvedWithPredicates;
}
/** Print all NFA states plus what alts they predict */
@Override
public String toString() {
StringBuilder buf = new StringBuilder();
buf.append(stateNumber).append(":{");
for (int i = 0; i < nfaConfigurations.size(); i++) {
NFAConfiguration configuration = nfaConfigurations.get(i);
if ( i>0 ) {
buf.append(", ");
}
buf.append(configuration);
}
buf.append("}");
return buf.toString();
}
public int getLookaheadDepth() {
return k;
}
public void setLookaheadDepth(int k) {
this.k = k;
if ( k > dfa.max_k ) { // track max k for entire DFA
dfa.max_k = k;
}
}
}