[antlr-interest] [antlr-dev] Generated code checks for backtracking even though backtracking is off

[Terence Parr]

Hi. [I'm moving this to the interest list as it is about using not building antlr]

Do you have backtrack=true anywhere?  do you have "=>" operators anywhere? I believe that is the only way it will wrap those actions.

Ter
On Feb 28, 2011, at 12:18 PM, Susanna Siebert wrote:

> Hi everybody,
> 
> we are trying to add custom bracematching to our language, Hop. For example, our functions are designed in the form action myAction .. end, where we are trying to match the "action" with the "end". To do that we added some semantic actions to the appropriate rules in the *.g file, that add some information about the position of the tokens to a hash table in a matcher module. This works fine except for the if-else-statements. These look like so:
> 
> if_statement    
>     :
>     firstif = IF root_expression THEN { symbol.add(new BlockDescriptor()); } block { symbol.popScope(); } firstend = END 
>     {
>         MatchKeyword keyword1 = new MatchKeyword();
>         keyword1.setMatchID(((CommonToken)$firstif).getStartIndex());
>         keyword1.setStartOffset(((CommonToken)$firstif).getStartIndex() - $firstif.getLine() + 1);
>         keyword1.setEndOffset(((CommonToken)$firstif).getStopIndex() - $firstif.getLine() + 2);
>         keyword1.setIsPrefix(true); 
>         MatchKeyword keyword2 = new MatchKeyword();
>         keyword2.setMatchID(((CommonToken)$firstif).getStartIndex());
>         keyword2.setStartOffset(((CommonToken)$firstend).getStartIndex() - $firstend.getLine() + 1);
>         keyword2.setEndOffset(((CommonToken)$firstend).getStopIndex() - $firstend.getLine() + 2);
>         keyword2.setIsPrefix(false); 
>         matcher.addMatch(keyword1, keyword2);
>     }
>     ((firstelse = ELSE IF root_expression THEN { symbol.add(new BlockDescriptor()); } block { symbol.popScope(); } secondend = END 
>     {
>         MatchKeyword keyword1 = new MatchKeyword();
>         keyword1.setMatchID(((CommonToken)$firstelse).getStartIndex());
>         keyword1.setStartOffset(((CommonToken)$firstelse).getStartIndex() - $firstelse.getLine() + 1);
>         keyword1.setEndOffset(((CommonToken)$firstelse).getStopIndex() - $firstelse.getLine() + 2);
>         keyword1.setIsPrefix(true); 
>         MatchKeyword keyword2 = new MatchKeyword();
>         keyword2.setMatchID(((CommonToken)$firstelse).getStartIndex());
>         keyword2.setStartOffset(((CommonToken)$secondend).getStartIndex() - $secondend.getLine() + 1);
>         keyword2.setEndOffset(((CommonToken)$secondend).getStopIndex() - $secondend.getLine() + 2);
>         keyword2.setIsPrefix(false); 
>         matcher.addMatch(keyword1, keyword2);
>     }
>     ) => (ELSE IF root_expression THEN block END))*  //else if blocks
>     ((secondelse = ELSE THEN { symbol.add(new BlockDescriptor()); } block { symbol.popScope(); } thirdend = END
>     {
>         MatchKeyword keyword1 = new MatchKeyword();
>         keyword1.setMatchID(((CommonToken)$secondelse).getStartIndex());
>         keyword1.setStartOffset(((CommonToken)$secondelse).getStartIndex() - $secondelse.getLine() + 1);
>         keyword1.setEndOffset(((CommonToken)$secondelse).getStopIndex() - $secondelse.getLine() + 2);
>         keyword1.setIsPrefix(true); 
>         MatchKeyword keyword2 = new MatchKeyword();
>         keyword2.setMatchID(((CommonToken)$secondelse).getStartIndex());
>         keyword2.setStartOffset(((CommonToken)$thirdend).getStartIndex() - $thirdend.getLine() + 1);
>         keyword2.setEndOffset(((CommonToken)$thirdend).getStopIndex() - $thirdend.getLine() + 2);
>         keyword2.setIsPrefix(false); 
>         matcher.addMatch(keyword1, keyword2);
>     }
>     ) => (ELSE THEN block END) )? 
>     ;
> 
> The problem is that when the code is generated, the semantic actions are being surrounded by an if-statement that checks state.backtracking (if (state.backtracking == 0) {}). For the if-then part of the rule, this check evaluates to true but for the else-if-then and else-then it evaluates to false because state.backtracking is 1. However, backtracking is turned off. 
> 
> My questions now are: 
> Why is a check for state.backtracking added when code is generated even if backtracking is turned off? 
> How can I make sure that the semantic actions of the else-if-then and else-then are being executed? 
> 
> I appreciate your help.
> 
> Best regards,
> 
> Susanna Siebert
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