org.antlr.v4.runtime

Class ParserInterpreter

java.lang.Object

org.antlr.v4.runtime.Recognizer<Token,ParserATNSimulator>

org.antlr.v4.runtime.Parser

org.antlr.v4.runtime.ParserInterpreter

public class ParserInterpreter
extends Parser

A parser simulator that mimics what ANTLR's generated parser code does. A ParserATNSimulator is used to make predictions via adaptivePredict but this class moves a pointer through the ATN to simulate parsing. ParserATNSimulator just makes us efficient rather than having to backtrack, for example. This properly creates parse trees even for left recursive rules. We rely on the left recursive rule invocation and special predicate transitions to make left recursive rules work. See TestParserInterpreter for examples.

Nested Class Summary

Nested classes/interfaces inherited from class org.antlr.v4.runtime.Parser

Parser.TraceListener, Parser.TrimToSizeListener

Field Summary

Fields

Modifier and Type	Field and Description
protected Deque<Pair<ParserRuleContext,Integer>>	_parentContextStack This stack corresponds to the _parentctx, _parentState pair of locals that would exist on call stack frames with a recursive descent parser; in the generated function for a left-recursive rule you'd see: private EContext e(int _p) throws RecognitionException { ParserRuleContext _parentctx = _ctx; // Pair.a int _parentState = getState(); // Pair.b ...
protected ATN	atn
protected DFA[]	decisionToDFA
protected String	grammarFileName
protected int	overrideDecision We need a map from (decision,inputIndex)->forced alt for computing ambiguous parse trees.
protected int	overrideDecisionAlt
protected int	overrideDecisionInputIndex
protected boolean	overrideDecisionReached
protected InterpreterRuleContext	overrideDecisionRoot What is the current context when we override a decisions? This tells us what the root of the parse tree is when using override for an ambiguity/lookahead check.
protected InterpreterRuleContext	rootContext
protected String[]	ruleNames
protected PredictionContextCache	sharedContextCache
protected String[]	tokenNames Deprecated.

Fields inherited from class org.antlr.v4.runtime.Parser

_buildParseTrees, _ctx, _errHandler, _input, _parseListeners, _precedenceStack, _syntaxErrors, matchedEOF

Fields inherited from class org.antlr.v4.runtime.Recognizer

_interp, EOF

Constructor Summary

Constructors

Constructor and Description
ParserInterpreter(String grammarFileName, Collection<String> tokenNames, Collection<String> ruleNames, ATN atn, TokenStream input) Deprecated. Use ParserInterpreter(String, Vocabulary, Collection, ATN, TokenStream) instead.
ParserInterpreter(String grammarFileName, Vocabulary vocabulary, Collection<String> ruleNames, ATN atn, TokenStream input)

Method Summary

Modifier and Type	Method and Description
void	addDecisionOverride(int decision, int tokenIndex, int forcedAlt) Override this parser interpreters normal decision-making process at a particular decision and input token index.
protected InterpreterRuleContext	createInterpreterRuleContext(ParserRuleContext parent, int invokingStateNumber, int ruleIndex) Provide simple "factory" for InterpreterRuleContext's.
void	enterRecursionRule(ParserRuleContext localctx, int state, int ruleIndex, int precedence)
ATN	getATN() Get the ATN used by the recognizer for prediction.
protected ATNState	getATNState()
String	getGrammarFileName() For debugging and other purposes, might want the grammar name.
InterpreterRuleContext	getOverrideDecisionRoot()
InterpreterRuleContext	getRootContext() Return the root of the parse, which can be useful if the parser bails out.
String[]	getRuleNames()
String[]	getTokenNames() Deprecated.
Vocabulary	getVocabulary() Get the vocabulary used by the recognizer.
ParserRuleContext	parse(int startRuleIndex) Begin parsing at startRuleIndex
protected void	recover(RecognitionException e) Rely on the error handler for this parser but, if no tokens are consumed to recover, add an error node.
protected Token	recoverInline()
void	reset() reset the parser's state
protected int	visitDecisionState(DecisionState p) Method visitDecisionState() is called when the interpreter reaches a decision state (instance of DecisionState).
protected void	visitRuleStopState(ATNState p)
protected void	visitState(ATNState p)

Methods inherited from class org.antlr.v4.runtime.Parser

addContextToParseTree, addParseListener, compileParseTreePattern, compileParseTreePattern, consume, dumpDFA, enterOuterAlt, enterRecursionRule, enterRule, exitRule, getATNWithBypassAlts, getBuildParseTree, getContext, getCurrentToken, getDFAStrings, getErrorHandler, getExpectedTokens, getExpectedTokensWithinCurrentRule, getInputStream, getInvokingContext, getNumberOfSyntaxErrors, getParseInfo, getParseListeners, getPrecedence, getRuleContext, getRuleIndex, getRuleInvocationStack, getRuleInvocationStack, getSourceName, getTokenFactory, getTokenStream, getTrimParseTree, inContext, isExpectedToken, isMatchedEOF, isTrace, match, matchWildcard, notifyErrorListeners, notifyErrorListeners, precpred, pushNewRecursionContext, removeParseListener, removeParseListeners, setBuildParseTree, setContext, setErrorHandler, setInputStream, setProfile, setTokenFactory, setTokenStream, setTrace, setTrimParseTree, triggerEnterRuleEvent, triggerExitRuleEvent, unrollRecursionContexts

Methods inherited from class org.antlr.v4.runtime.Recognizer

action, addErrorListener, getErrorHeader, getErrorListenerDispatch, getErrorListeners, getInterpreter, getRuleIndexMap, getSerializedATN, getState, getTokenErrorDisplay, getTokenType, getTokenTypeMap, removeErrorListener, removeErrorListeners, sempred, setInterpreter, setState

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

grammarFileName

protected final String grammarFileName

atn

protected final ATN atn

decisionToDFA

protected final DFA[] decisionToDFA

sharedContextCache

protected final PredictionContextCache sharedContextCache

tokenNames

@Deprecated
protected final String[] tokenNames

Deprecated.

ruleNames

protected final String[] ruleNames

_parentContextStack

protected final Deque<Pair<ParserRuleContext,Integer>> _parentContextStack

This stack corresponds to the _parentctx, _parentState pair of locals that would exist on call stack frames with a recursive descent parser; in the generated function for a left-recursive rule you'd see: private EContext e(int _p) throws RecognitionException { ParserRuleContext _parentctx = _ctx; // Pair.a int _parentState = getState(); // Pair.b ... } Those values are used to create new recursive rule invocation contexts associated with left operand of an alt like "expr '*' expr".

overrideDecision

protected int overrideDecision

We need a map from (decision,inputIndex)->forced alt for computing ambiguous parse trees. For now, we allow exactly one override.

overrideDecisionInputIndex

protected int overrideDecisionInputIndex

overrideDecisionAlt

protected int overrideDecisionAlt

overrideDecisionReached

protected boolean overrideDecisionReached

overrideDecisionRoot

protected InterpreterRuleContext overrideDecisionRoot

What is the current context when we override a decisions? This tells us what the root of the parse tree is when using override for an ambiguity/lookahead check.

rootContext

protected InterpreterRuleContext rootContext

Constructor Detail

ParserInterpreter

@Deprecated
public ParserInterpreter(String grammarFileName,
                                     Collection<String> tokenNames,
                                     Collection<String> ruleNames,
                                     ATN atn,
                                     TokenStream input)

Deprecated. Use ParserInterpreter(String, Vocabulary, Collection, ATN, TokenStream) instead.

ParserInterpreter

public ParserInterpreter(String grammarFileName,
                         Vocabulary vocabulary,
                         Collection<String> ruleNames,
                         ATN atn,
                         TokenStream input)

Method Detail

reset

public void reset()

Description copied from class: Parser

reset the parser's state

Overrides:

reset in class Parser

getATN

public ATN getATN()

Description copied from class: Recognizer

Get the ATN used by the recognizer for prediction.

Specified by:

getATN in class Recognizer<Token,ParserATNSimulator>

Returns:

The ATN used by the recognizer for prediction.

getTokenNames

@Deprecated
public String[] getTokenNames()

Deprecated.

Description copied from class: Recognizer

Used to print out token names like ID during debugging and error reporting. The generated parsers implement a method that overrides this to point to their String[] tokenNames.

Specified by:

getTokenNames in class Recognizer<Token,ParserATNSimulator>

getVocabulary

public Vocabulary getVocabulary()

Description copied from class: Recognizer

Get the vocabulary used by the recognizer.

Overrides:

getVocabulary in class Recognizer<Token,ParserATNSimulator>

Returns:

A Vocabulary instance providing information about the vocabulary used by the grammar.

getRuleNames

public String[] getRuleNames()

Specified by:

getRuleNames in class Recognizer<Token,ParserATNSimulator>

getGrammarFileName

public String getGrammarFileName()

Description copied from class: Recognizer

For debugging and other purposes, might want the grammar name. Have ANTLR generate an implementation for this method.

Specified by:

getGrammarFileName in class Recognizer<Token,ParserATNSimulator>

parse

public ParserRuleContext parse(int startRuleIndex)

Begin parsing at startRuleIndex

enterRecursionRule

public void enterRecursionRule(ParserRuleContext localctx,
                               int state,
                               int ruleIndex,
                               int precedence)

Overrides:

enterRecursionRule in class Parser

getATNState

protected ATNState getATNState()

visitState

protected void visitState(ATNState p)

visitDecisionState

protected int visitDecisionState(DecisionState p)

Method visitDecisionState() is called when the interpreter reaches a decision state (instance of DecisionState). It gives an opportunity for subclasses to track interesting things.

createInterpreterRuleContext

protected InterpreterRuleContext createInterpreterRuleContext(ParserRuleContext parent,
                                                              int invokingStateNumber,
                                                              int ruleIndex)

Provide simple "factory" for InterpreterRuleContext's.

Since:

4.5.1

visitRuleStopState

protected void visitRuleStopState(ATNState p)

addDecisionOverride

public void addDecisionOverride(int decision,
                                int tokenIndex,
                                int forcedAlt)

Override this parser interpreters normal decision-making process at a particular decision and input token index. Instead of allowing the adaptive prediction mechanism to choose the first alternative within a block that leads to a successful parse, force it to take the alternative, 1..n for n alternatives. As an implementation limitation right now, you can only specify one override. This is sufficient to allow construction of different parse trees for ambiguous input. It means re-parsing the entire input in general because you're never sure where an ambiguous sequence would live in the various parse trees. For example, in one interpretation, an ambiguous input sequence would be matched completely in expression but in another it could match all the way back to the root. s : e '!'? ; e : ID | ID '!' ; Here, x! can be matched as (s (e ID) !) or (s (e ID !)). In the first case, the ambiguous sequence is fully contained only by the root. In the second case, the ambiguous sequences fully contained within just e, as in: (e ID !). Rather than trying to optimize this and make some intelligent decisions for optimization purposes, I settled on just re-parsing the whole input and then using {link Trees#getRootOfSubtreeEnclosingRegion} to find the minimal subtree that contains the ambiguous sequence. I originally tried to record the call stack at the point the parser detected and ambiguity but left recursive rules create a parse tree stack that does not reflect the actual call stack. That impedance mismatch was enough to make it it challenging to restart the parser at a deeply nested rule invocation. Only parser interpreters can override decisions so as to avoid inserting override checking code in the critical ALL(*) prediction execution path.

Since:

4.5.1

getOverrideDecisionRoot

public InterpreterRuleContext getOverrideDecisionRoot()

recover

protected void recover(RecognitionException e)

Rely on the error handler for this parser but, if no tokens are consumed to recover, add an error node. Otherwise, nothing is seen in the parse tree.

recoverInline

protected Token recoverInline()

getRootContext

public InterpreterRuleContext getRootContext()

Return the root of the parse, which can be useful if the parser bails out. You still can access the top node. Note that, because of the way left recursive rules add children, it's possible that the root will not have any children if the start rule immediately called and left recursive rule that fails.

Since:

4.5.1