Re: Evolutionary User Strategy - A Compromise

[Erik Sandberg]

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