[antlr-interest] Re: antlr bug or grammar problem?

[kozchris]

Skipped over your question, sorry. 

The problem I'm seeing is that the expr rule is being run when the
line parsed starts with an ID token.

I expect the expr rule to only run when the line parsed starts with
the BECAME_TRUE, BECAME_FALSE or CHANGED tokens.
 
Thanks,
Chris



--- In antlr-interest at yahoogroups.com, "kozchris" <csnyder at a...> wrote:
> shouldn't a line like this 
> 
> > > ( BECAME_TRUE | BECAME_FALSE | CHANGED ) => expr
> 
> produce code like this
> 
> > > 		switch ( LA(1)) {
> > > 		case BECAME_TRUE:
> > > 		case BECAME_FALSE:
> > > 		case CHANGED:
> > > 		{
> > > 			expr();
> 
> 
> 
> --- In antlr-interest at yahoogroups.com, Monty Zukowski <monty at c...>
wrote:
> > 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
> > ANSI C/GCC transformation toolkit -- 
> > http://www.codetransform.com/gcc.html
> > Embrace the Decay -- http://www.codetransform.com/EmbraceDecay.html
> > 
> > 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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