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package com.sun.msv.verifier.regexp;
import com.sun.msv.grammar.AttributeExp;
import com.sun.msv.grammar.ChoiceExp;
import com.sun.msv.grammar.ConcurExp;
import com.sun.msv.grammar.DataExp;
import com.sun.msv.grammar.ElementExp;
import com.sun.msv.grammar.Expression;
import com.sun.msv.grammar.ExpressionPool;
import com.sun.msv.grammar.ExpressionVisitorExpression;
import com.sun.msv.grammar.InterleaveExp;
import com.sun.msv.grammar.ListExp;
import com.sun.msv.grammar.MixedExp;
import com.sun.msv.grammar.OneOrMoreExp;
import com.sun.msv.grammar.OtherExp;
import com.sun.msv.grammar.ReferenceExp;
import com.sun.msv.grammar.SequenceExp;
import com.sun.msv.grammar.ValueExp;
/**
* removes all unnecessary expressions and
* creates an expression that consists of required attributes and choices only.
*
* <XMP>
* For example,
*
* <choice>
* <element />
* <attribute />
* </choice>
*
* will be converted to
*
* <empty />
*
* because no attribute is required. But
*
* <choice>
* <attribute />
* <attribute />
* </choice>
*
* will remain the same because one or the other is required.
*
* this method also removes SequenceExp.
*
* <sequence>
* <attribute name="A" />
* <attribute name="B" />
* </sequence>
*
* will be converted to
*
* <attribute name="A" />
*
* This function object is used only for error recovery.
* Resulting expressions always consist only of <choice>s and <attribute>s.
* </XMP>
*
* @author <a href="mailto:kohsuke.kawaguchi@eng.sun.com">Kohsuke KAWAGUCHI</a>
*/
public class AttributePicker implements ExpressionVisitorExpression
{
private final ExpressionPool pool;
public AttributePicker( ExpressionPool pool ) {
this.pool = pool;
}
public Expression onElement( ElementExp exp ) {
return AttributeExp.epsilon;
}
public Expression onMixed( MixedExp exp ) {
return exp.exp.visit(this);
}
public Expression onAnyString() {
return Expression.epsilon;
}
public Expression onEpsilon() {
return Expression.epsilon;
}
public Expression onNullSet() {
return Expression.nullSet;
}
public Expression onRef( ReferenceExp exp ) {
return exp.exp.visit(this);
}
public Expression onOther( OtherExp exp ) {
return exp.exp.visit(this);
}
public Expression onData( DataExp exp ) {
return Expression.epsilon;
}
public Expression onValue( ValueExp exp ) {
return Expression.epsilon;
}
public Expression onList( ListExp exp ) {
return Expression.epsilon;
}
public Expression onAttribute( AttributeExp exp ) {
return exp;
}
public Expression onOneOrMore( OneOrMoreExp exp ) {
// reduce A+ -> A
return exp.exp.visit(this);
}
public Expression onSequence( SequenceExp exp ) {
Expression ex1 = exp.exp1.visit(this);
Expression ex2 = exp.exp2.visit(this);
if(ex1.isEpsilonReducible()) {
if(ex2.isEpsilonReducible()) return Expression.epsilon;
else return ex2;
}
else
return ex1;
}
public Expression onInterleave( InterleaveExp exp ) {
Expression ex1 = exp.exp1.visit(this);
Expression ex2 = exp.exp2.visit(this);
if(ex1.isEpsilonReducible()) {
if(ex2.isEpsilonReducible()) return Expression.epsilon;
else return ex2;
} else
return ex1;
}
public Expression onConcur( ConcurExp exp ) {
// abandon concur.
return Expression.epsilon;
}
public Expression onChoice( ChoiceExp exp ) {
Expression ex1 = exp.exp1.visit(this);
Expression ex2 = exp.exp2.visit(this);
// if one of choice is epsilon-reducible,
// the entire choice becomes optional.
// optional attributes have to be removed from the result.
if( ex1.isEpsilonReducible() || ex2.isEpsilonReducible() )
return Expression.epsilon;
return pool.createChoice(ex1,ex2);
}
}