Re: Proposal: get rid of ly:export

[Ian Hulin]

Hi David,
(see below)

On 06/11/11 09:43, David Kastrup wrote:
> 
> Hi,
> 
> I've been annoyed in the past by the presence of ly:export since
> it creates timing problems in the parser and lexer.  I propose
> completely removing it.  As a replacement in the rare situations
> where it might be applicable, I propose moving the $ syntax, now
> only used inside of #{ ... #}, to Lilypond in general, in order to
> indicate auto-export at the direct lexical level where it makes
> sense.
> 
> So that #{ ... #} would still be able to access music function
> variables inside, it would inherit the lexical environment of its
> encompassing definition.
> 
> This would imply that #{ ... #$argument ... #} would _cease_
> working.  Instead you would have to write #{ ... #argument ... #}
> in order to get a Scheme argument.  But at least #{ ...
> #$defaultpaper ... #} would work the same in #{ ... #} as outside.
> 
> If ly:export is removed, we can split the work of #( ... ) into two
> phases: at the lexical stage, the expression is read.  While 
> parsing, it is evaluated.  In that manner, we get rid of
> synchronization problems.
> 
> In contrast, $ would read and evaluate in one piece.  As one
> benefit, we would get rid of errormessages involving
> \lilytmpvarxxxx pseudovariables.
> 
> This change would definitely cause problems to existing code.
> Automatic conversion seems only semi-feasible.
> 
> But it would give $ straightforward semantics everywhere (it would
> carry a meaning always in Lilypond, never in Scheme).  And removing
> ly:export, which requires messing up the logical order and timing
> of lexing/parsing, would be a definite improvement, while still
> providing its functionality in a non-obscure way.
> 
The main thing you'll need to look at for possible side-effects is the
coding of the tagline in scm/titling-init.ly, as this is potentially
used by default in any LilyPond compilation.  Here's the stuff from
scm/titling-init.ly.

tagline = \markup {
  \with-url

  #"http://lilypond.org/";
  \line {

    %% 2014 = em dash.

    #(ly:export
      (format #f "Music engraving by LilyPond ~a~awww.lilypond.org"
       (lilypond-version)
       (ly:wide-char->utf-8 #x2014)
       ))
  }
}

If as part of this patch you can re-code so we don't have to use this
nonsense, so much the better, it's a major PITA for Guile V2 migration
as it crashes Guile in phase 2 of LilyPond initialization and I can't
yet see why.

Cheers,

Ian