Hi Simon,
On Wed, Mar 25, 2015 at 1:29 PM, Simon Albrecht <simon.albre...@mail.de>
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 <simon.albre...@mail.de>
> 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
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