[antlr-interest] antlr-interest Digest, Vol 94, Issue 25

[John D. Mitchell]

On Sep 25, 2012, at 12:00 , antlr-interest-request at antlr.org wrote:

> From: Stuart Maclean <stuart at apl.washington.edu>
> Subject: [antlr-interest] C grammar question
> To: antlr-interest at antlr.org
> Message-ID: <5060CB88.9040406 at apl.washington.edu>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
> 
> Hi from a newbie.  I have been using Antlr3 for about 4 days.
> 
> First, a quick question.  is the mailing list archive searchable in any 
> way??  I suspect not (those MailMan interfaces never seem to be), but 
> perhaps I am just not seeing it.

http://antlr.markmail.org/


> My real question relates to the C grammar, bundled in 
> examples-v3/java/C.  If I build it as is and run against the following 
> input:
> 
> typedef void (*a2)(int i);
> 
> it will print that both 'a2' and 'i' are new types.  But only 'a2' is a 
> new type here, 'i' should not be seen as a new type.  I can see that the 
> way the 'isTypedef' info is being communicated from the 'declaration' 
> rule to the 'direct_declarator' rule, but the logic is failing if the 
> parser has to visit the
> 
>     '('  declarator ')'
> 
> branch of the direct_declarator rule. which it does for the input above. 
> To suppress 'i' being seen as a new type, I added this action to the 
> direct_declarator rule:
> 
>     |    '( declarator ')'
>             { $declaration::isTypedef=false; }
> 
> but it seems like a hack and I am wondering if there is some cleaner way 
> to do this.

At the top of that grammar is a note from Ter about the simplified use of a symbol table for dealing with types so it's not too much of a surprise that it's over permissive in this case.

> A further question.  What does this mean (in the same C.g)?
> 
> type_id
>     :   {isTypeName(input.LT(1).getText())}? IDENTIFIER
> 
> Is this a 'pre action'??  If so, what does the '?' mean?  I can't find 
> any notes about what this construct represents?

That's a "semantic predicate". Check out the antlr docs for more info.

Cheers,
John