[antlr-interest] parse error because of AST rewrite rules?

[Jim Idle]

On 09/21/2009 11:07 AM, Stefan Oestreicher wrote:
> Hi,
>
> I'm working on a grammar for a simple programming language and I'd like
> to support variable declarations like that:
> int a, b = 3
>
> I started out with the following rule:
>
> variableDeclaration
>      :   type ID ( COMMA ID )* ( ASSIGN expression )?
>      ;
>    
Do you really mean that, or do you mean:

(type (ASSIGN expression)?) ( COMMA type (ASSIGN expression)?)*


However, it looks like your simpleVariable and listVariable need left 
factoring (bring all the common things in to one rule and branch alts 
where they differ.

Jim
> Now I'd like to generate an AST for the above example that looks like that:
> ^(VAR_DEF int a)
> ^(VAR_DEF int b)
> ^(= a 3)
> ^(= b a)
>
> So I've tried it with the following rules:
>
> --- grammar snippet ---
> variableDeclaration
>      :    simpleVariableDeclaration
>      |    listVariableDeclaration
>      ;
>
> simpleVariableDeclaration
>      :    type ID ( ASSIGN expression )?
>          ->     ^(VAR_DEF ID type)
>                  ^(ASSIGN ID expression)?
>      ;
>
> listVariableDeclaration
>      :    type first=ID ( COMMA other+=ID )+
> listVariableAssignment[$first, $other]?
>          ->     ^(VAR_DEF $first type)
>                  ^(VAR_DEF $other type)
>              listVariableAssignment?
>      ;
>
> listVariableAssignment[pANTLR3_COMMON_TOKEN first, pANTLR3_VECTOR other]
>      :    ASSIGN expression
>          ->     ^(ASSIGN {$first} expression)
>                  ^(ASSIGN {$other} {$first})+
>      ;
> --- /grammar snippet ---
>
> I've also tried this simpler variant for listVariableDeclaration:
>
> --- grammar snippet ---
> listVariableDeclaration
>      :    (    type first=ID ( COMMA other+=ID )+
>              ->     ^(VAR_DEF $first type)
>                      ^(VAR_DEF $other type)
>           )
>           (    ASSIGN expression
>               ->    ^(ASSIGN $first expression)
>                      ^(ASSIGN $other $first)+
>           )?
>      ;
> --- /grammar snippet ---
>
> The modified rules still produce a correct parse tree in the interpreter
> but the generated code raises a parse error. It either complains about
> the assignment operator after the ID list or about the semicolon the
> terminates the declaration (not shown in the example).
> If I remove the rewrite rules there is no problem.
>
> I'd appreciate any hint about what I'm doing wrong. I'm using the C
> target btw, version 3.1.3.
>
> Thanks,
>
> Stefan
>
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