[antlr-interest] What about grammar inheritance?

[Terence Parr]

On Monday, December 8, 2003, at 12:47 PM, brian-l-smith at uiowa.edu wrote:

> Quoting Terence Parr <parrt at cs.usfca.edu>:
>
>> On Monday, December 8, 2003, at 12:58  AM, Ruslan Zasukhin wrote:
>>
>>> on 12/8/03 10:03 AM, Silvain Piree at s.piree at enneya.com wrote:
>>>
>>>> On the antlr website, the paper "ANTLR 3 Whitepaper"
>>>> mentions "dropping inheritance" as one of the features of
>>>> ANTLR 3.
>>>>
>>>> Will there be an alternative grammar re-use mechanism
>>>> in ANTLR 3?
>>
>> Either inheritance or delegation or something...haven't turned my
>> thoughts to this yet. :)
>
> I don't understand what the "Grammar reuse via RCS concepts" idea is.
>
> I think I mentioned this before, but I'll mention it again. SDF/SDF2 
> has a
> really good grammar module system that is much more flexible than 
> ANTLR's
> current grammar inheritence system. Whereas ANTLR's system is similar 
> to subtype
> polymorphism (subclassing), SDF's mechanism is more like parametrically
> polymorphism (generics). You are encouraged to break up your grammar 
> into
> reusable pieces, which you can then assemble in different ways, 
> overriding and
> parameterizing rules as necessary.
>
> For a simple example, let's say you have a module for the lexical 
> syntaxes of a
> bunch of languages; e.g. Java, C#, Standard ML, Lisp, CORBA IDL, etc. 
> It is
> commonly the case that any new language you create will have a lexical 
> syntax
> that is basically a combination of different subsets of these 
> languages. So, it
> seems you would want to do something like this (the meta-language is 
> made up):
>
> lexical grammar MyLanguageLexicalGramar is
> begin
>     StringLiteral imported from SQL;       -- We love single quotes
>     Identifier    imported from StandardML;-- why not allow primes in 
> ID's
>     Comment       imported from PLSQL;     -- the ultimate comment 
> marker
> end;

Hi Brian,

Yep, that's what I meant by delegations.

lexer JavaLexer;

delegate ID, INT, FLOAT to CGrammar;
....

> This is one very useful idea that is basically impossible to implement 
> using
> ANTLR's current inheritence system (no multiple inheritence). It is 
> easily done
> in SDF2's module system. Also, the rule template mechanism I suggested 
> a long
> time ago can be implemented through this module system--each template 
> rule is
> just a parameterized (sub-)module.

Interesting.  I'll bring this back up when I get more into the overall 
functionality...i'm still working on the engine.

Ter
--
Professor Comp. Sci., University of San Francisco
Creator, ANTLR Parser Generator, http://www.antlr.org
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