[antlr-interest] Rewrite action causing error in parser?

[Maximilien Colange]

It appears that this "bug" is frequently reported.
It would be nice if ANTLR raised an error (or a warning) when a token is 
given a reference in a syntactic predicate.

However, I do not know whether it is easy to detect. I already 
encountered this problem, and it occured in a "hidden" ANTLR-generated 
syntactic predicate. I am afraid the error is difficult to detect in 
such cases.

And just for curiosity, why is not it possible to reference local 
variables or to assign from token in a syntactic predicate ?

-- 
Maximilien

Le 10/15/11 11:34 PM, Jim Idle a écrit :
> Your problem does not look to be the rewrite rule, but the fact that you
> are referencing a local variable in a predicate, or have tried to assign
> from a token in a predicate.
>
> Look for something like this
>
> ((id=IDENTIFIER)=>  id=IDENTIFIER)? ....
>
>
> But regardless, this is the rewrite rule that is the problem as far as I
> can see. Try commenting it out for instance.
>
> Jim
>
>> -----Original Message-----
>> From: antlr-interest-bounces at antlr.org [mailto:antlr-interest-
>> bounces at antlr.org] On Behalf Of Ross Bamford
>> Sent: Saturday, October 15, 2011 5:40 AM
>> To: antlr-interest at antlr.org
>> Subject: [antlr-interest] Rewrite action causing error in parser?
>>
>> Hi all,
>>
>> I have a grammar I'm currently working on (posted in another thread the
>> other day), which has the following rule:
>>
>> meth_call_expr
>>    :   (id = IDENTIFIER DOT)? func_call_expr ->  ^(METHOD_CALL {
>> ($id==null) ?
>> adaptor.create(SELF, "SELF") : adaptor.create(IDENTIFIER,
>> $id.getText()) }
>> func_call_expr)
>>    ;
>>
>> As you can see, I'm using an action in the rewrite rule to insert
>> either the
>> (optional) IDENTIFIER, or an imaginary SELF node if IDENTIFIER is not
>> specified. The problem I'm having is that this generates a parser that
>> won't compile. Specifically, it generates the following bit of code
>> (edited by hand for brevity and to highlight the error):
>>
>> /* **** [ CODE ] **** */
>>      // $ANTLR start synpred6_BasicLang
>>      public final void synpred6_BasicLang_fragment() throws
>> RecognitionException {
>>
>>          Token =null; //<-- ERROR HERE
>>
>>          /* ... later on ... */
>>
>>          switch (alt23) {
>>              case 1 :
>>                  //
>> C:\\Users\\chantelle\\workspace\\basiclang\\src\\com\\roscopeco\\basicl
>> ang\\parser\\BasicLang.g:99:8:
>> id= IDENTIFIER DOT
>>                  {
>>
>> id=(Token)match(input,IDENTIFIER,FOLLOW_IDENTIFIER_in_synpred6_BasicLan
>> g232);
>> if (state.failed) return ; //<-- AND HERE
>>
>>                  match(input,DOT,FOLLOW_DOT_in_synpred6_BasicLang234);
>> if
>> (state.failed) return ;
>>
>>                  }
>>                  break;
>>
>>          }
>> /* **** [ END ] **** */
>>
>> Obviously the problem is the "Token =null" line, which should be "Token
>> id = null". Changing it by hand fixes the errors and makes the parser
>> work as expected.
>>
>> So I have two questions - is this the right way to go about inserting
>> an imaginary token if an optional token isn't in the input, and if so,
>> what am I doing wrong to cause the error above?
>>
>> Thanks in advance,
>> Ross
>>
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