com.oracle.truffle.regex.tregex.parser.ast.visitors

Class MarkLookBehindEntriesVisitor

java.lang.Object

com.oracle.truffle.regex.tregex.parser.ast.visitors.NFATraversalRegexASTVisitor

com.oracle.truffle.regex.tregex.parser.ast.visitors.MarkLookBehindEntriesVisitor

public class MarkLookBehindEntriesVisitor
extends NFATraversalRegexASTVisitor

For all lookbehind assertions, mark all states where the assertion may begin. If an assertion may begin before the root of the AST, the AST is wrapped into a non-capturing group and prepended with a sequence of optional and non-optional any-char matchers, as shown in the following example: /(?<=ab)/ is transformed to /(?:[_any_][_any_](?:|[_any_](?:|[_any_])))(?<=ab)/. The sequence of non-optional any-char matchers is called "prefix", and is necessary for cases where we want to start searching for a regex match on a random position in a string. When starting on any other index than 0, we decrease the index by the length of the prefix (but stop at position 0) and thereby guarantee that lookbehind matches are found, but no regex match prior to the actual starting index is found. When starting at index 0, the prefix is ignored. When starting at index 1, just the last element of the prefix is used, and so on.

This entire mechanism assumes that all lookbehind assertion have a fixed length!

See Also:

RegexAST.createPrefix()

Field Summary

Fields inherited from class com.oracle.truffle.regex.tregex.parser.ast.visitors.NFATraversalRegexASTVisitor

ast

Constructor Summary

Constructors

Constructor and Description
MarkLookBehindEntriesVisitor(RegexAST ast)

Method Summary

Modifier and Type	Method and Description
protected boolean	canPruneAfterUnconditionalFinalState()
protected void	enterLookAhead(LookAheadAssertion assertion)
protected boolean	isBuildingDFA()
protected void	leaveLookAhead(LookAheadAssertion assertion)
void	run()
protected void	visit(RegexASTNode target) Visit the next successor found.

Methods inherited from class com.oracle.truffle.regex.tregex.parser.ast.visitors.NFATraversalRegexASTVisitor

calcQuantifierGuards, canTraverseCaret, caretsOnPath, dollarsOnPath, getCurrentMatchedConditionGroups, getGroupBoundaries, getLastDollarOnPath, getMatchedConditionGroups, getQuantifierGuardsOnPath, getTraversableLookBehindAssertions, hasQuantifierGuards, isReverse, run, setCanTraverseCaret, setMatchedConditionGroups, setReverse, setTraversableLookBehindAssertions

Methods inherited from class java.lang.Object

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

Constructor Detail

MarkLookBehindEntriesVisitor

public MarkLookBehindEntriesVisitor(RegexAST ast)

Method Detail

run

public void run()

visit

protected void visit(RegexASTNode target)

Description copied from class: NFATraversalRegexASTVisitor

Visit the next successor found.

Specified by:

visit in class NFATraversalRegexASTVisitor

enterLookAhead

protected void enterLookAhead(LookAheadAssertion assertion)

Specified by:

enterLookAhead in class NFATraversalRegexASTVisitor

leaveLookAhead

protected void leaveLookAhead(LookAheadAssertion assertion)

Specified by:

leaveLookAhead in class NFATraversalRegexASTVisitor

isBuildingDFA

protected boolean isBuildingDFA()

Specified by:

isBuildingDFA in class NFATraversalRegexASTVisitor

canPruneAfterUnconditionalFinalState

protected boolean canPruneAfterUnconditionalFinalState()

Specified by:

canPruneAfterUnconditionalFinalState in class NFATraversalRegexASTVisitor