Re: [updated PATCH] %language declaration

[Paolo Bonzini]

> 1. Bison should never support a language with a different basic syntax 
> than C/C++ since we don't want Bison to have to parse such a language in 
> actions.
>
> 2. Bison might one day support such a language but Bison should parse 
> actions for them horribly incorrectly.  Thus, we'll refuse to have 
> %language now to ensure that no one tries to parse them correctly then.
>
> Obviously it's not #2.  If it's #1, what's the harm in supporting 
> %language now?  That doesn't prevent us from opposing specific languages 
> later.

It's neither #1 nor #2.  It's more like "People might one day want Bison 
to support a language with a different basic syntax than C/C++, and this 
might require massive changes to the parser, making it close to 
unmaintainable.  Thus, we'll refuse to have %language now to set a 
precedent that Bison's operation must be as language-independent as 
possible (as opposed to the m4 skeletons)."

I agree that this doesn't prevent us from opposing specific languages 
later.  Also, Java also sets a (IMHO good) precedent of how to make 
changes to Bison for the sake of supporting more languages: no change to 
the parser, limited modifications to make the m4 skeletons more generic, 
but *no change* to the grammar parser.

> Then again, if we're not willing to parse any other syntax, I 
> guess that means we won't be adding very many other languages.

Actually, I think we can parse a lot of languages with some limitations. 
in their use.  Perl definitely has problems because of hieroglyphics in 
the name -- this might extend to PHP in the future if we support $foo. 
Python has some because of the indentation.

OTOH, Lisp has different semantics for apostrophes but you can restrict 
yourself to (quote a b c) instead of '(a b c).  Likewise Ruby and PHP 
interpolate variables within a quoted string, and in this case Bison may 
parse "the first token is $1" incorrectly.  But even with these 
limitations, the parser could "just work" for a lot of languages.

(Note that I'm not endorsing in any way the creation of Bison skeletons 
for these languages...) ;-)

> Sorry to force you to play devil's advocate, but I feel like I'm missing 
> the point.

No problem, it can work well.  I hope this is clearer now?

Paolo