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Re: Input variables and Scheme

From: Han-Wen Nienhuys
Subject: Re: Input variables and Scheme
Date: Mon, 25 Sep 2006 03:16:28 +0200
User-agent: Thunderbird (X11/20060913)

Michael Welsh Duggan schreef:
Michael Welsh Duggan <address@hidden> writes:

Michael Welsh Duggan <address@hidden> writes:

Either the documentation for 12.2.1 "Input variables and Scheme" is
deprecated, or somthing is broken.  Using the following input:

\version "2.9.19"

traLaLa = { c'4 d'4 }

#(define newLa (map ly:music-deep-copy
  (list traLaLa traLaLa)))
#(define twice
  (make-sequential-music newLa))

{ \twice }

I get the following output:

lilypond -f ps /home/md5i/lily/test27.ly
GNU LilyPond 2.9.19.mwd
Processing `/home/md5i/lily/test27.ly'
Parsing.../home/md5i/lily/test27.ly:2:3: While evaluating arguments to list in 
expression (list traLaLa traLaLa):
/home/md5i/lily/test27.ly:2:3: Unbound variable: traLaLa
Both this and the subsequent bug I have posted are rooted in the same
problem.  The asignment rule in parser.yy isn't triggered until after
the subsequent scheme expression is lexed.  Since scheme code is
executed at lex time, the scheme expression is effectively happening
before the assignment preceeding it.

One possible way to fix this problem is to pass on the result of the
`read' call to the parser to evaluate, instead of doing both in
ly_parse_scm (internal_ly_parse_scm).  If any of the primary
developers think this is a good idea, I'll have a stab at implementing

Hmm, but what about ly:export ? It sets the lexer token type of a scheme expression depending on the outcome of the evaluation. It's not used very often, but we have to tread carefully with compatibility.

Han-Wen Nienhuys - address@hidden - http://www.xs4all.nl/~hanwen

LilyPond Software Design
 -- Code for Music Notation

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