[antlr-interest] antlr bug or grammar problem?

[Monty Zukowski]

A syntactic predicate doesn't work by modifying the lookahead, it 
actually tests the grammar fragment in 'guessing' mode and then if that 
is ok it will proceed.  I don't think you've found a bug in ANTLR.  
However, you were looking at the code for a reason.  What's the 
original bug?

Monty

ANTLR & Java Consultant -- http://www.codetransform.com
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On Sep 23, 2004, at 11:10 AM, kozchris wrote:

> I'm using antlr 2.7.4.
> I've run the grammar building both a cpp and java version with same
> results.
>
> You can see the grammar file here
> http://www.synergyss.com/SCRExpression.g.
> and the java output here
> http://www.synergyss.com/SCRExpressionParser.java
>
> The issue is showing up in the parser code generated for rule
> eventExpr on line 279.
> The line:
>   ( BECAME_TRUE | BECAME_FALSE | CHANGED ) => expr {printf("processing
> simple event expr\n");}
>
> is showing up as this in the generated parser.
>
> <<<< begin code snip
> 		switch ( LA(1)) {
> 		case BOOLEAN:
> 		case DoubleDoubleConst:
> 		case FloatDoubleConst:
> 		case LongDoubleConst:
> 		case IntBinaryConst:
> 		case IntHexConst:
> 		case LongHexConst:
> 		case UnsignedHexConst:
> 		case IntOctalConst:
> 		case LongOctalConst:
> 		case UnsignedOctalConst:
> 		case IntIntConst:
> 		case LongIntConst:
> 		case UnsignedIntConst:
> 		case LPAREN:
> 		case PLUS:
> 		case MINUS:
> 		case LNOT:
> 		case BNOT:
> 		case BECAME_TRUE:
> 		case BECAME_FALSE:
> 		case CHANGED:
> 		case ID:
> 		{
> 			expr();
> 			astFactory.addASTChild(currentAST, returnAST);
> 			if ( inputState.guessing==0 ) {
> 				printf("processing simple event expr\n");
> 			}
> 			eventExpr_AST = (AST)currentAST.root;
> 			break;
> 		}
> <<<< end code snip
>
> What is strange is that if I change line 281 from:
>   ( BECAME_TRUE | BECAME_FALSE | CHANGED ) => expr {printf("processing
> simple event expr\n");}
>
> to:
>
>   ( BECAME_TRUE | BECAME_FALSE | CHANGED ) => simpleEventExpr
> {printf("processing simple event expr\n");}
>
> the code generated is correct.
>
> <<<< begin code snip
> 		switch ( LA(1)) {
> 		case BECAME_TRUE:
> 		case BECAME_FALSE:
> 		case CHANGED:
> 		{
> 			simpleEventExpr();
> 			astFactory.addASTChild(currentAST, returnAST);
> 			if ( inputState.guessing==0 ) {
> 				printf("processing simple event expr\n");
> 			}
> 			eventExpr_AST = (AST)currentAST.root;
> 			break;
> 		}
> <<<< end code snip
>
> Any ideas on how to solve this problem?
>
> Thanks for the help.
> Chris
>
>
>
>
>
>
> Yahoo! Groups Links
>
>
>
>
>
>
>



 
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