xtc.parser
Class ChoiceExpander

java.lang.Object
  xtc.tree.Visitor
      xtc.parser.GrammarVisitor
          xtc.parser.ChoiceExpander

public class ChoiceExpander
extends GrammarVisitor

Visitor to expand choices by inlining productions. This visitor inlines transient productions if they are essentially the only element appearing in ordered choices' alternatives.

Note that this visitor requires that text-only productions have been marked as such, that all value elements have been added to the grammar (notably, for generic productions), and that the grammar's productions have been reference counted. Also note that this visitor may result in new opportunities for the elimination of dead productions.

This visitor assumes that the entire grammar is contained in a single module.

Version:

$Revision: 1.36 $

Author:

Robert Grimm

Nested Class Summary

static class

ChoiceExpander.Mode The processing mode.

Field Summary

protected boolean	hasState The flag for whether the grammar has the state attribute.
protected ChoiceExpander.Mode	mode The current processing mode.

Fields inherited from class xtc.parser.GrammarVisitor

analyzer, isBound, isLastElement, isPredicate, isRepeatedOnce, isTopLevel, isVoided, needsSequence, runtime, transformInPlace

Constructor Summary

ChoiceExpander(Runtime runtime, Analyzer analyzer)
Create a new choice expander.

Method Summary

protected NonTerminal	candidate(Sequence alternative, boolean top) Determine whether the specified alternative is a candidate for replacement.
protected void	inlined(Production p) Record that the specified production has been inlined and, if necessary, print a message to the console.
java.lang.Object	visit(Module m) Visit the specified grammar.
Element	visit(OrderedChoice c) Visit the specified ordered choice.
Element	visit(Sequence s) Visit the specified sequence.
Element	visit(ValueElement v) Visit the specified value element.

Methods inherited from class xtc.parser.GrammarVisitor

visit, visit, visit, visit, visit, visit, visit, visit, visit, visit, visit, visit, visit

Methods inherited from class xtc.tree.Visitor

dispatch, equals, hashCode, iterate, map, mapInPlace, unableToVisit, visit

Methods inherited from class java.lang.Object

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

Field Detail

hasState

protected boolean hasState

The flag for whether the grammar has the state attribute.

mode

protected ChoiceExpander.Mode mode

The current processing mode.

Constructor Detail

ChoiceExpander

public ChoiceExpander(Runtime runtime,
                      Analyzer analyzer)

Create a new choice expander.

Parameters:

runtime - The runtime.

analyzer - The analyzer utility.

Method Detail

candidate

protected NonTerminal candidate(Sequence alternative,
                                boolean top)

Determine whether the specified alternative is a candidate for replacement. If the alternative is a candidate, this method returns the nonterminal for inlining. Otherwise, it returns null.

Parameters:

alternative - The alternative.

top - The flag for whether the alternative appears in a top-level choice.

Returns:

The candidate nonterminal.

inlined

protected void inlined(Production p)

Record that the specified production has been inlined and, if necessary, print a message to the console.

Parameters:

p - The production.

visit

public java.lang.Object visit(Module m)

Visit the specified grammar.

Overrides:

visit in class GrammarVisitor

visit

public Element visit(OrderedChoice c)

Visit the specified ordered choice.

Overrides:

visit in class GrammarVisitor

visit

public Element visit(Sequence s)

Visit the specified sequence.

Overrides:

visit in class GrammarVisitor

visit

public Element visit(ValueElement v)

Visit the specified value element.