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

[Monty Zukowski]

Hey, I used to work on that grammar!  Anyhow, this may be a bug in 
ANTLR.  Syntactic predicates are used to disambiguate.  Here, ANTLR 
sees no ambiguities between the alternatives, so it doesn't use the 
syntactic predicate.  If it were generating a syn pred you would see 
guessing mode incremented and the decremented at the end of the 
predicate.

Try a semantic predicate instead 
{LA(1)==BECAME_TRUE||LA(1)==BECAME_FALSE||LA(1)==CHANGED}?

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 11:55 AM, kozchris 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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