Might be an idea to look at Antlr then ... I don't know how effective it would be, but part of the purpose behind the v3 rewrite is to increase the number of languages that Antlr can generate. If you can define the grammar in Antlr it could then chuck out a lexer/parser written in Scheme :-) Is the current lily parser hand-written? At the expense of some upfront work, this could save a lot of effort downstream if so.
It does sound very much as though what you want to do, is what Antlr is designed to do ... you say Scheme rocks for tree manipulation? Well Antlr was DESIGNED for tree manipulation (and other related tasks :-) ... And yes, preservation of white space is apparently fairly easy. Although, I'm half inclined to say that if you "convert-ly" a piece, then it will or can output stuff according to a "pretty print" standard. Take a look at Antlr - www.antlr.org. I'd go straight to v3, which is due for release this summer. What you would need to do is define the lily grammar using a BNF style notation (I think the technical term for the style of grammar is LA or LLA). Antlr itself is written in Java - run it over your grammar and it will spit out a lexer and parser for you. You could either use the current C++ templates which would create your lexer and parser in C++ for feeding the results to Scheme, or write a bunch of Scheme templates and output the lexer and parser directly in Scheme. I don't mean to teach grandma to suck eggs but it sounds (from the implication that the parser is mixed-language) that you're not using a compiler-compiler such as flex/Bison, PCCTS or Antlr. And of course, going down this route, things head towards the typical nix "toolkit" approach :-) Grammars to input lily ASTs in various versions, grammars to output "pretty printed" or converted .ly files in various versions, grammars to transform ASTs especially ones generated from eg abc, Sibelius, Personal Composer files :-) Just link the appropriate sequence of tools and away you go ... I can see it being a lot of up-front work. The question is, will it save more than that in future ... and I think your answer to "is it possible" is "yes", just is it worth it? Cheers, Wol -----Original Message----- From: Erik Sandberg [mailto:[EMAIL PROTECTED] Sent: 12 July 2006 19:08 To: lilypond-user@gnu.org Cc: Anthony Youngman Subject: Re: Evolutionary User Strategy - A Compromise On Wednesday 12 July 2006 17:22, Anthony Youngman wrote: > I don't really understand grammars etc (which is why my DATABASIC thing > is on/off :-). > > But from my experience with Antlr, I don't see why you should lose > stuff. Your PEG article mentions ASTs. I don't see that converting a .ly > file into an AST can be that hard. So, for example, we write a Antlr > grammar that creates a lexer/parser that turns the .ly into an AST. We > now write another grammar that converts the AST to a .ly file. A problem here is code duplication; it takes some effort to maintain two parsers instead of one. I think it will be difficult to automatically test that the current antlr parser corresponds well with the actual grammar the current lilypond version uses. I have been thinking about moving lily's entire parser out to Scheme; this way we could keep one old parser for each version, and use it to generate an AST, which then is converted nicely using rules written in Scheme (Scheme rocks when it comes to tree manipulation). I'm not sure if it's possible though. BTW: Will your solution handle whitespace nicely? -- Erik * ************************************************************************ * This transmission is intended for the named recipient only. It may contain private and confidential information. If this has come to you in error you must not act on anything disclosed in it, nor must you copy it, modify it, disseminate it in any way, or show it to anyone. Please e-mail the sender to inform us of the transmission error or telephone ECA International immediately and delete the e-mail from your information system. Telephone numbers for ECA International offices are: Sydney +61 (0)2 8272 5300, Hong Kong + 852 2121 2388, London +44 (0)20 7351 5000 and New York +1 212 582 2333. * ************************************************************************ * _______________________________________________ lilypond-user mailing list lilypond-user@gnu.org http://lists.gnu.org/mailman/listinfo/lilypond-user
