idea for convert-ly substitute

[Erik Sandberg]

Hi,

Inspired by recent discussions on lily-user, I have a new idea on how to 
maintain compatibility between versions. The idea is to dump syntax 
expression to disk, and let the user archive those files. Then, a conversion 
script can be written which translates those expressions between versions. 
Each version can then import a syntax expression, and convert it back to 
a .ly file.

This requires a bunch of changes:
- _all_ parsing needs to go through syntax expressions (this includes toplevel 
stuff like \version and \book).
- Make it possible for the parser to catch each syntax expression just before 
it's evaluated. This way, stuff like \relative will not be expanded.
- Write a syntax-expression->ly converter. This should be easy; it could even 
be feasible to preserve original whitespace to some degree.
- Write a script that handles conversion of syntax expressions between 
versions. I think this will be both cleaner and easier to do than convert-ly.

-- 
Erik