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

[Johan Vromans]

Hartmut Leister <address@hidden> writes:

> 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)
>     }

I use a technique similar to this to produce (guitar) scores with and
without capo.

An include file defined a specific symbol, or not. 

It capo is wanted, the file contains a single line:

  withCapo = 1

Otherwise, it is empty, leaving the symbol withCapo undefined.

In the code I use

  \ifDefinedThenElse #'withCapo

    { % code for the capo case
    }

    { % code for the non-capo case
    }


The definition of ifDefinedThenElse is quite simple:

  %% \ifDefinedThenElse symbol expression else-expression
  %%
  %% If the symbol is defined, returns the expression.
  %% Otherwise, returns the else-expression.

  ifDefinedThenElse =
  #(define-music-function (parser location sym music else) (symbol? ly:music? 
ly:music?)
    (if (defined? sym)
     music else))

  %% Example:
  %%
  %% \ifDefinedThen #'leadWords  \lyricsto lead \ifDefined #'leadWords

HTH,

-- Johan