Re: Scheme void function problems

[David Nalesnik]

Hi Simon,

On Wed, Mar 25, 2015 at 1:29 PM, Simon Albrecht <address@hidden> wrote:

Hello,

thanks a lot for your thoughts, David.

Am 25.03.2015 um 16:33 schrieb David Nalesnik:

Hi Simon,

I can't judge whether this is getting closer to you want, but maybe my observations can help.

On Wed, Mar 25, 2015 at 9:17 AM, Simon Albrecht <address@hidden> wrote:

Hello,

I’m experimenting with an implementation of automatic tagline language selection and currently have two problems with the void function \language that I adapted from music-functions-init.ly:
– I can’t get the first, optional argument to work; it needs to be explicitly given or Lily will take the string as first argument – although it’s required to be a symbol.

I haven't succeeded in making this work with the optional argument in the first position.  I moved it last.

From the design point of view I think it’s necessary to have it first: it’s much more intuitive to write \language output "deutsch" than \language "deutsch" output.
I don’t quite get why having the optional argument first doesn’t work: after all, this is commonly used in music functions and scheme functions. But apparently define-void-function is implemented differently.

No, the same issues exist here with music and scheme functions.  Try the below with define-scheme-function and define-music-function.  (With the latter you'll need to add some music return--like #{ #} )

 

This would then mean that one has to always specify the first argument, which is not the most elegant form. I’ll probably switch to using three distinct functions \language, \inputLanguage and \outputLanguage (with the names being subject to discussion of course). 

Sure, it could be first.  And that is more intuitive!  You could do:

 \version "2.19.16"

#(define output-language '())

language =

#(define-void-function (parser location channel language)

   ((symbol? 'general) string?)

   (_i "Define languages for input (i.e. set note names for @var{language}),

output (i.e. display tagline and table of contents in @var{language}), or both.")

   (if (not (eq? channel 'output))

    (note-names-language parser language))

   (if (not (eq? channel 'input))

       (set! output-language (string->symbol language)))

   )

\language \default "deutsch" %% works

%\language general "deutsch" %% works

%\language "deutsch" %% does not

{

  c

}

[...etc...]

%%%

The problem with the last invocation is this.  LilyPond considers whether the first argument you give it--"deutsch"--is a symbol.  It isn't, so it uses 'general.  Then, it looks further on for a suitable value for 'language', not for 'channel'. The next thing encountered is the music _expression_, which raises an error because it's not a string....  

--David