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// Copyright (c) 2012-2022 The ANTLR Project. All rights reserved.
// Use of this file is governed by the BSD 3-clause license that
// can be found in the LICENSE.txt file in the project root.
package antlr
type LL1Analyzer struct {
atn *ATN
}
func NewLL1Analyzer(atn *ATN) *LL1Analyzer {
la := new(LL1Analyzer)
la.atn = atn
return la
}
// - Special value added to the lookahead sets to indicate that we hit
// a predicate during analysis if {@code seeThruPreds==false}.
//
// /
const (
LL1AnalyzerHitPred = TokenInvalidType
)
// *
// Calculates the SLL(1) expected lookahead set for each outgoing transition
// of an {@link ATNState}. The returned array has one element for each
// outgoing transition in {@code s}. If the closure from transition
// <em>i</em> leads to a semantic predicate before Matching a symbol, the
// element at index <em>i</em> of the result will be {@code nil}.
//
// @param s the ATN state
// @return the expected symbols for each outgoing transition of {@code s}.
func (la *LL1Analyzer) getDecisionLookahead(s ATNState) []*IntervalSet {
if s == nil {
return nil
}
count := len(s.GetTransitions())
look := make([]*IntervalSet, count)
for alt := 0; alt < count; alt++ {
look[alt] = NewIntervalSet()
lookBusy := NewJStore[ATNConfig, Comparator[ATNConfig]](&ObjEqComparator[ATNConfig]{})
seeThruPreds := false // fail to get lookahead upon pred
la.look1(s.GetTransitions()[alt].getTarget(), nil, BasePredictionContextEMPTY, look[alt], lookBusy, NewBitSet(), seeThruPreds, false)
// Wipe out lookahead for la alternative if we found nothing
// or we had a predicate when we !seeThruPreds
if look[alt].length() == 0 || look[alt].contains(LL1AnalyzerHitPred) {
look[alt] = nil
}
}
return look
}
// *
// Compute set of tokens that can follow {@code s} in the ATN in the
// specified {@code ctx}.
//
// <p>If {@code ctx} is {@code nil} and the end of the rule containing
// {@code s} is reached, {@link Token//EPSILON} is added to the result set.
// If {@code ctx} is not {@code nil} and the end of the outermost rule is
// reached, {@link Token//EOF} is added to the result set.</p>
//
// @param s the ATN state
// @param stopState the ATN state to stop at. This can be a
// {@link BlockEndState} to detect epsilon paths through a closure.
// @param ctx the complete parser context, or {@code nil} if the context
// should be ignored
//
// @return The set of tokens that can follow {@code s} in the ATN in the
// specified {@code ctx}.
// /
func (la *LL1Analyzer) Look(s, stopState ATNState, ctx RuleContext) *IntervalSet {
r := NewIntervalSet()
seeThruPreds := true // ignore preds get all lookahead
var lookContext PredictionContext
if ctx != nil {
lookContext = predictionContextFromRuleContext(s.GetATN(), ctx)
}
la.look1(s, stopState, lookContext, r, NewJStore[ATNConfig, Comparator[ATNConfig]](&ObjEqComparator[ATNConfig]{}), NewBitSet(), seeThruPreds, true)
return r
}
//*
// Compute set of tokens that can follow {@code s} in the ATN in the
// specified {@code ctx}.
//
// <p>If {@code ctx} is {@code nil} and {@code stopState} or the end of the
// rule containing {@code s} is reached, {@link Token//EPSILON} is added to
// the result set. If {@code ctx} is not {@code nil} and {@code addEOF} is
// {@code true} and {@code stopState} or the end of the outermost rule is
// reached, {@link Token//EOF} is added to the result set.</p>
//
// @param s the ATN state.
// @param stopState the ATN state to stop at. This can be a
// {@link BlockEndState} to detect epsilon paths through a closure.
// @param ctx The outer context, or {@code nil} if the outer context should
// not be used.
// @param look The result lookahead set.
// @param lookBusy A set used for preventing epsilon closures in the ATN
// from causing a stack overflow. Outside code should pass
// {@code NewSet<ATNConfig>} for la argument.
// @param calledRuleStack A set used for preventing left recursion in the
// ATN from causing a stack overflow. Outside code should pass
// {@code NewBitSet()} for la argument.
// @param seeThruPreds {@code true} to true semantic predicates as
// implicitly {@code true} and "see through them", otherwise {@code false}
// to treat semantic predicates as opaque and add {@link //HitPred} to the
// result if one is encountered.
// @param addEOF Add {@link Token//EOF} to the result if the end of the
// outermost context is reached. This parameter has no effect if {@code ctx}
// is {@code nil}.
func (la *LL1Analyzer) look2(s, stopState ATNState, ctx PredictionContext, look *IntervalSet, lookBusy *JStore[ATNConfig, Comparator[ATNConfig]], calledRuleStack *BitSet, seeThruPreds, addEOF bool, i int) {
returnState := la.atn.states[ctx.getReturnState(i)]
la.look1(returnState, stopState, ctx.GetParent(i), look, lookBusy, calledRuleStack, seeThruPreds, addEOF)
}
func (la *LL1Analyzer) look1(s, stopState ATNState, ctx PredictionContext, look *IntervalSet, lookBusy *JStore[ATNConfig, Comparator[ATNConfig]], calledRuleStack *BitSet, seeThruPreds, addEOF bool) {
c := NewBaseATNConfig6(s, 0, ctx)
if lookBusy.Contains(c) {
return
}
_, present := lookBusy.Put(c)
if present {
return
}
if s == stopState {
if ctx == nil {
look.addOne(TokenEpsilon)
return
} else if ctx.isEmpty() && addEOF {
look.addOne(TokenEOF)
return
}
}
_, ok := s.(*RuleStopState)
if ok {
if ctx == nil {
look.addOne(TokenEpsilon)
return
} else if ctx.isEmpty() && addEOF {
look.addOne(TokenEOF)
return
}
if ctx != BasePredictionContextEMPTY {
removed := calledRuleStack.contains(s.GetRuleIndex())
defer func() {
if removed {
calledRuleStack.add(s.GetRuleIndex())
}
}()
calledRuleStack.remove(s.GetRuleIndex())
// run thru all possible stack tops in ctx
for i := 0; i < ctx.length(); i++ {
returnState := la.atn.states[ctx.getReturnState(i)]
la.look2(returnState, stopState, ctx, look, lookBusy, calledRuleStack, seeThruPreds, addEOF, i)
}
return
}
}
n := len(s.GetTransitions())
for i := 0; i < n; i++ {
t := s.GetTransitions()[i]
if t1, ok := t.(*RuleTransition); ok {
if calledRuleStack.contains(t1.getTarget().GetRuleIndex()) {
continue
}
newContext := SingletonBasePredictionContextCreate(ctx, t1.followState.GetStateNumber())
la.look3(stopState, newContext, look, lookBusy, calledRuleStack, seeThruPreds, addEOF, t1)
} else if t2, ok := t.(AbstractPredicateTransition); ok {
if seeThruPreds {
la.look1(t2.getTarget(), stopState, ctx, look, lookBusy, calledRuleStack, seeThruPreds, addEOF)
} else {
look.addOne(LL1AnalyzerHitPred)
}
} else if t.getIsEpsilon() {
la.look1(t.getTarget(), stopState, ctx, look, lookBusy, calledRuleStack, seeThruPreds, addEOF)
} else if _, ok := t.(*WildcardTransition); ok {
look.addRange(TokenMinUserTokenType, la.atn.maxTokenType)
} else {
set := t.getLabel()
if set != nil {
if _, ok := t.(*NotSetTransition); ok {
set = set.complement(TokenMinUserTokenType, la.atn.maxTokenType)
}
look.addSet(set)
}
}
}
}
func (la *LL1Analyzer) look3(stopState ATNState, ctx PredictionContext, look *IntervalSet, lookBusy *JStore[ATNConfig, Comparator[ATNConfig]], calledRuleStack *BitSet, seeThruPreds, addEOF bool, t1 *RuleTransition) {
newContext := SingletonBasePredictionContextCreate(ctx, t1.followState.GetStateNumber())
defer func() {
calledRuleStack.remove(t1.getTarget().GetRuleIndex())
}()
calledRuleStack.add(t1.getTarget().GetRuleIndex())
la.look1(t1.getTarget(), stopState, newContext, look, lookBusy, calledRuleStack, seeThruPreds, addEOF)
}
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