[antlr-interest] 3.0 multiple language support

[Thomas Dudziak]

Sebastian Kaliszewski wrote:

>Tiller, Michael (M.M.) wrote:
>  
>
>>>How about allowing different language versions of the same action in
>>>the same file? Something like:
>>>
>>>my_prod
>>>  : my_subpod %C{ /* here C action comes */  }
>>>              %J{ /* here java action goes */ }
>>>              %P{ /* here python action goes */ }
>>>      
>>>
>>Of the options I have seen so far, I prefer the one where the grammar
>>just has macros and the actions themselves are specified outside the
>>grammar, e.g.
>>
>>some_rule
>>   : a:A "," b:B << process_some_rule(a,b); >>
>>
>>And then you could weave together an action file with a grammar file.
>>So you might have a C++ action file:
>>
>>void process_some_rule(A *a, B* b)
>>{
>>  /* Do something very general in this language */
>>}
>>
>>    
>>
>
>I really don't like this. Actions (esp. predicates) are part of the grammar. 
>Separating them makes code much harder to read, analyse and maitain, as one 
>has to jump around the code text.
>Macros might be a nice idea, but they should be intermixable with the 
>parser/lexer definition in the same file.
>  
>
I find Michaels solution much easier to maintain. Imagine the Java 
grammar with embedded actions for all supported languages - it will 
surely be not readable anymore. Defining labels, e.g. 
"process_some_rule" is far better IMO. You can simply add all 
information as parameters that is required by the action. The net result 
is that the grammars themselves are target-language-independent 
(remember the newbie asking about a Java version for the SQL grammar ?) 
and you have the action in a concise form, perhaps in a single class. Or 
Antlr generates abstract method declarations (for C++/C#/Java) in the 
parser that the developer has to override in a concrete parser subclass 
(template and hook).
There are a few situations where this might seem like overkill (e.g. 
maintaining and using a counter for a ()* subrule that shall be 
traversed like 20 times), but there might be better ways to handle these 
situations (e.g. defining syntax for it - say, ()[20] - and letting 
Antlr work out the details).

Tom



 
Yahoo! Groups Links

<*> To visit your group on the web, go to:
    http://groups.yahoo.com/group/antlr-interest/

<*> To unsubscribe from this group, send an email to:
    antlr-interest-unsubscribe at yahoogroups.com

<*> Your use of Yahoo! Groups is subject to:
    http://docs.yahoo.com/info/terms/