[antlr-interest] adding "version" option to ANTLR grammars

[Gary R. Van Sickle]

> From: Anthony W. Youngman
> 
> In message <673774B77DFB453C985A9D7053EC2FF7 at DFW5RB41>, Gary 
> R. Van Sickle <g.r.vansickle at att.net> writes
> >> Another improvement would be to allow a comma-separated list.
> >> With it one can record all versions of ANTLR, with which 
> the grammar 
> >> works without any modifications.
> >
> >The trouble with that is that it forces the user to predict 
> the future.
> >Maybe it will work with the next fifty versions, which may only have 
> >changes which don't affect the ultimate interpretation, such as bug 
> >fixes, speed improvements, and the like, but there's no way 
> to specify that.
> >
> >The only way this sort of thing works is for the source file 
> to declare 
> >"this is the standard I was written to".  It is then up to the 
> >interpreters, past, present, and future, to either modify their 
> >interpretation to match that of the specified standard (i.e. future 
> >ANTLR versions "degrading" their
> >interpretation) or simply bail (e.g. ANTLR 3.1.2 tries to read a 
> >grammar that says its written to the ANTLR 8.5.6 standard, 
> which it of 
> >course has no idea what that even is, so it can't possibly 
> interpret it).
> 
> Look at how Lilypond handles versioning (oh - and I think 
> lily's parser got rewritten in Antlr a while back - I'm not 
> sure but I certainly see the odd Antlr ref on the mailing list :-)
> 
> Each version of Lily knows what is the oldest version of the 
> syntax it supports, so if 2.12.2 sees "version 2.12.0" in an 
> input file it's quite happy. If it sees 2.11.59 it bails with 
> "this input file is too old - run convert-ly". I don't know 
> what it would do if it saw 2.12.6.
> 
> But basically, it knows at what point there were incompatible 
> syntax changes, and objects if you try to feed it an old 
> file. Okay, it might (or might not) be a bit more work in 
> Antlr deciding at what points to break backwards 
> compatibility, but it might also make life easier - keep 
> compatibility over several versions because you can, then 
> break it and Antlr knows to object about old input.
> 
> Cheers,
> Wol
> --
> Anthony W. Youngman - anthony at thewolery.demon.co.uk

Yep, that's exactly what I'm suggesting.  The file indicates what version of
the language it was written to, the interpreter of the file decides what to
do based on that version info.

-- 
Gary R. Van Sickle