Re: if/then/else in Lilypond with config file

[Urs Liska]

Am 16.01.2015 um 01:37 schrieb Craig Parker-Feldmann:
> > Is there a possibility to do something like this?
> >
> >      if( custom_cfg_flag)
> >      {
> >          % default score combination
> >          % (e.g. with header and chords)
> >      }
> >      else
> >      {
> >          % some other combination
> >          % (e.g. only melody)
> >      }

Yes, definitely.
I don't really know what you want yet, but in general you can do such 
stuff with Scheme.

Try this:

%%%%%%%%%%%

%#(define some-cfg-variable #t)
#(define some-cfg-variable #f)

musicOne = { c'' d'' c'' }
musicTwo = { c' d' c' }

\score {
  <<
    \new Staff \musicOne
    #(if some-cfg-variable
         #{ \new Staff \musicTwo #})
  >>
}

%%%%%%%%%%%

Of course there is much more to it, but it may give you a first 
impression of what is possible.

The "#(" starts a Scheme expression.
with "#{ #}" inside a Scheme expression you can produce LilyPond output 
again.

HTH
Urs

> I have also always wanted LilyPond to provide me with
> the code-writing niceties which C offers. Here is a
> method which enables me to use blocks of preprocessor
> directives in the manner which I am used to:
>
> #define BEGRIFF
>
> #ifdef BEGRIFF
>    #define INTEGER_CONSTANT 1
> #else
>    #define INTEGER_CONSTANT 43
> #endif
>
> My operating system is Linux. For its GNU Compiler Suite
> there is the preprocessor ``gpp''. This preprocessor can
> be invoked with the ``-T'' option, to instruct it to
> understand macros which are written in the style that
> TeX (and LilyPond) use.
>
> The first shell script processes a the file
> ``if-else-1a-input.ly''.
>
> -----if-else-1a-input.ly-----
> % Within a region which is commented, you can embed your
> % macro definitions.
> % \define{conditionalPackage}
> % \ifdef{conditionalPackage}
> %   \define{musicPassage}{\musicPassageAlpha}
> % \else
> %   \define{musicPassage}{\musicPassageBeta}
> % \endif
> \version "2.12.3"
> \header { title = "Using if/else Constructs by Means of GPP" }
> musicPassageAlpha = { c'4 d' e' f' }
> musicPassageBeta = { b,4 a, g, f, }
> \score {
>    <<
>      \new Staff \musicPassage
>    >>
>    \layout { }
> }
> % EOF
> -----------------------
>
> Here is the shell script that does the work:
>
> -----if-else-1a.sh-----
> #! /bin/bash
> # Invokes ``[[gpp]]'' in order to process an input file
> # which has a macro definition in it formatted in the
> # manner which TeX formats things.
> INPUT_FILE=if-else-1a-input.ly
> OUTPUT_FILE=if-else-1a-output.ly
> gpp -T -o $OUTPUT_FILE $INPUT_FILE && \
>    echo 'Output file "'$OUTPUT_FILE'" successfully written.'
> # EOF
> -----------------------
>
> The second shell script processes a the file
> ``if-else-1b-input.ly''. This document has an ``undef''
> preprocessor directive in it.
>
> -----if-else-1b-input.ly-----
> % Within a region which is commented, you can embed your
> % macro definitions.
> % This version puts an ``undef'' preprocessor
> % directive in the macro definition.
> % \define{conditionalPackage}
> % \undef{conditionalPackage}
> % \ifdef{conditionalPackage}
> %   \define{musicPassage}{\musicPassageAlpha}
> % \else
> %   \define{musicPassage}{\musicPassageBeta}
> % \endif
> \version "2.12.3"
> \header { title="Using if/else Constructs by Means of GPP" }
> musicPassageAlpha = { c'4 d' e' f' }
> musicPassageBeta = { b'''4 a''' g''' f''' }
> \score {
>    <<
>      \new Staff \musicPassage
>    >>
>    \layout { }
> }
> % EOF
> -----------------------
>
> Here is the shell script that does the work:
>
> -----if-else-1b.sh-----
> #! /bin/bash
> # Invokes ``[[gpp]]'' in order to process an input file
> # which has a macro definition in it formatted in the
> # manner which TeX formats things.
> INPUT_FILE=if-else-1b-input.ly
> OUTPUT_FILE=if-else-1b-output.ly
> gpp -T -o $OUTPUT_FILE $INPUT_FILE && \
>    echo 'Output file "'$OUTPUT_FILE'" successfully written.'
> # EOF
> -----------------------
>
>
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