Re: [Lilypond-auto] Issue 2872 in lilypond: Patch: Provide define-session and define-session-public commands

[lilypond]

Comment #11 on issue 2872 by address@hidden: Patch: Provide define-session and  
define-session-public commands
http://code.google.com/p/lilypond/issues/detail?id=2872

add-new-clef is a public function, and it is unlikely that anybody changes  
this function from one session to the next.  Instead, it is getting used.   
If we take a look at this function, we see
(define-public (add-new-clef clef-name clef-glyph clef-position octavation  
c0-position)
  "Append the entries for a clef symbol to supported clefs and
@code{c0-pitch-alist}."
  (set! supported-clefs
        (acons clef-name (list clef-glyph clef-position octavation)  
supported-clefs))
  (set! c0-pitch-alist
        (acons clef-glyph c0-position c0-pitch-alist)))

And this means that we want to reset supported-clefs and c0-pitch-alist at  
the start of the next session.  Those are defined with define-public and  
define, respectively, so you can replace them with define-session-public  
and define-session.  Why is supported-clefs public?  There is an incredibly  
stupid thing called memoize-clef-names in scm/define-music-display-methods  
that will only work the first time it is called.  So we want to replace  
the "memoize location" defined with
(define clef-name-alist #f)
also with a define-session, so that this will work more often than just in  
a single session.  It would actually make more sense to remember the last  
_supported-clefs_ for memoization (rather than just a flag), and if it is  
not eq? to the current supported-clefs, it gets regenerated.  In that  
manner, one can even do memoization across sessions (meaning that  
clef-name-alist and last-supported-clefs themselves don't need to be  
per-session) and only have clef-name-alist recalculated if  
last-supported-clefs is no longer the eq? to supported-clefs since last use.