173 lines
7.6 KiB
Python
173 lines
7.6 KiB
Python
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#
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# Copyright (c) 2012-2017 The ANTLR Project. All rights reserved.
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# Use of this file is governed by the BSD 3-clause license that
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# can be found in the LICENSE.txt file in the project root.
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#/
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from antlr4.IntervalSet import IntervalSet
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from antlr4.Token import Token
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from antlr4.PredictionContext import PredictionContext, SingletonPredictionContext, PredictionContextFromRuleContext
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from antlr4.RuleContext import RuleContext
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from antlr4.atn.ATN import ATN
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from antlr4.atn.ATNConfig import ATNConfig
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from antlr4.atn.ATNState import ATNState, RuleStopState
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from antlr4.atn.Transition import WildcardTransition, NotSetTransition, AbstractPredicateTransition, RuleTransition
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class LL1Analyzer (object):
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#* Special value added to the lookahead sets to indicate that we hit
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# a predicate during analysis if {@code seeThruPreds==false}.
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#/
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HIT_PRED = Token.INVALID_TYPE
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def __init__(self, atn:ATN):
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self.atn = atn
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#*
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# Calculates the SLL(1) expected lookahead set for each outgoing transition
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# of an {@link ATNState}. The returned array has one element for each
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# outgoing transition in {@code s}. If the closure from transition
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# <em>i</em> leads to a semantic predicate before matching a symbol, the
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# element at index <em>i</em> of the result will be {@code null}.
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#
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# @param s the ATN state
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# @return the expected symbols for each outgoing transition of {@code s}.
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#/
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def getDecisionLookahead(self, s:ATNState):
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if s is None:
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return None
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count = len(s.transitions)
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look = [] * count
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for alt in range(0, count):
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look[alt] = set()
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lookBusy = set()
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seeThruPreds = False # fail to get lookahead upon pred
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self._LOOK(s.transition(alt).target, None, PredictionContext.EMPTY,
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look[alt], lookBusy, set(), seeThruPreds, False)
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# Wipe out lookahead for this alternative if we found nothing
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# or we had a predicate when we !seeThruPreds
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if len(look[alt])==0 or self.HIT_PRED in look[alt]:
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look[alt] = None
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return look
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#*
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# Compute set of tokens that can follow {@code s} in the ATN in the
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# specified {@code ctx}.
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#
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# <p>If {@code ctx} is {@code null} and the end of the rule containing
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# {@code s} is reached, {@link Token#EPSILON} is added to the result set.
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# If {@code ctx} is not {@code null} and the end of the outermost rule is
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# reached, {@link Token#EOF} is added to the result set.</p>
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#
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# @param s the ATN state
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# @param stopState the ATN state to stop at. This can be a
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# {@link BlockEndState} to detect epsilon paths through a closure.
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# @param ctx the complete parser context, or {@code null} if the context
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# should be ignored
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#
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# @return The set of tokens that can follow {@code s} in the ATN in the
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# specified {@code ctx}.
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#/
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def LOOK(self, s:ATNState, stopState:ATNState=None, ctx:RuleContext=None):
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r = IntervalSet()
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seeThruPreds = True # ignore preds; get all lookahead
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lookContext = PredictionContextFromRuleContext(s.atn, ctx) if ctx is not None else None
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self._LOOK(s, stopState, lookContext, r, set(), set(), seeThruPreds, True)
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return r
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#*
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# Compute set of tokens that can follow {@code s} in the ATN in the
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# specified {@code ctx}.
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#
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# <p>If {@code ctx} is {@code null} and {@code stopState} or the end of the
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# rule containing {@code s} is reached, {@link Token#EPSILON} is added to
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# the result set. If {@code ctx} is not {@code null} and {@code addEOF} is
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# {@code true} and {@code stopState} or the end of the outermost rule is
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# reached, {@link Token#EOF} is added to the result set.</p>
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#
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# @param s the ATN state.
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# @param stopState the ATN state to stop at. This can be a
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# {@link BlockEndState} to detect epsilon paths through a closure.
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# @param ctx The outer context, or {@code null} if the outer context should
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# not be used.
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# @param look The result lookahead set.
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# @param lookBusy A set used for preventing epsilon closures in the ATN
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# from causing a stack overflow. Outside code should pass
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# {@code new HashSet<ATNConfig>} for this argument.
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# @param calledRuleStack A set used for preventing left recursion in the
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# ATN from causing a stack overflow. Outside code should pass
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# {@code new BitSet()} for this argument.
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# @param seeThruPreds {@code true} to true semantic predicates as
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# implicitly {@code true} and "see through them", otherwise {@code false}
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# to treat semantic predicates as opaque and add {@link #HIT_PRED} to the
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# result if one is encountered.
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# @param addEOF Add {@link Token#EOF} to the result if the end of the
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# outermost context is reached. This parameter has no effect if {@code ctx}
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# is {@code null}.
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#/
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def _LOOK(self, s:ATNState, stopState:ATNState , ctx:PredictionContext, look:IntervalSet, lookBusy:set,
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calledRuleStack:set, seeThruPreds:bool, addEOF:bool):
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c = ATNConfig(s, 0, ctx)
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if c in lookBusy:
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return
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lookBusy.add(c)
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if s == stopState:
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if ctx is None:
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look.addOne(Token.EPSILON)
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return
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elif ctx.isEmpty() and addEOF:
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look.addOne(Token.EOF)
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return
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if isinstance(s, RuleStopState ):
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if ctx is None:
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look.addOne(Token.EPSILON)
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return
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elif ctx.isEmpty() and addEOF:
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look.addOne(Token.EOF)
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return
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if ctx != PredictionContext.EMPTY:
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# run thru all possible stack tops in ctx
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for i in range(0, len(ctx)):
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returnState = self.atn.states[ctx.getReturnState(i)]
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removed = returnState.ruleIndex in calledRuleStack
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try:
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calledRuleStack.discard(returnState.ruleIndex)
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self._LOOK(returnState, stopState, ctx.getParent(i), look, lookBusy, calledRuleStack, seeThruPreds, addEOF)
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finally:
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if removed:
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calledRuleStack.add(returnState.ruleIndex)
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return
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for t in s.transitions:
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if type(t) == RuleTransition:
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if t.target.ruleIndex in calledRuleStack:
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continue
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newContext = SingletonPredictionContext.create(ctx, t.followState.stateNumber)
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try:
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calledRuleStack.add(t.target.ruleIndex)
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self._LOOK(t.target, stopState, newContext, look, lookBusy, calledRuleStack, seeThruPreds, addEOF)
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finally:
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calledRuleStack.remove(t.target.ruleIndex)
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elif isinstance(t, AbstractPredicateTransition ):
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if seeThruPreds:
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self._LOOK(t.target, stopState, ctx, look, lookBusy, calledRuleStack, seeThruPreds, addEOF)
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else:
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look.addOne(self.HIT_PRED)
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elif t.isEpsilon:
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self._LOOK(t.target, stopState, ctx, look, lookBusy, calledRuleStack, seeThruPreds, addEOF)
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elif type(t) == WildcardTransition:
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look.addRange( range(Token.MIN_USER_TOKEN_TYPE, self.atn.maxTokenType + 1) )
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else:
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set_ = t.label
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if set_ is not None:
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if isinstance(t, NotSetTransition):
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set_ = set_.complement(Token.MIN_USER_TOKEN_TYPE, self.atn.maxTokenType)
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look.addSet(set_)
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