Re: Language selection code

[Simon Albrecht]

Am 27.03.2015 um 14:38 schrieb David Nalesnik:
> Hi Simon,
>
>
> On Thu, Mar 26, 2015 at 6:43 PM, Simon Albrecht 
> <address@hidden <mailto:address@hidden>> wrote:
>
> [...]
>
>     So the roadmap would include
>     – discussing design and coding (?)
>
>
> I haven't gone through this thoroughly, but I did notice that an 
> invalid statement like this
> \language general.deutsch.foo
> isn't gracefully dealt with.
>
> I haven't studied this enough to diagnose the problem, but I did 
> notice the following:
>
> % extended from music-functions-init.ly:603 
> <http://music-functions-init.ly:603>
> language =
> #(define-void-function
>   (parser location arg)
>   ;; Usage:
>   ;; \language input.LANG or
>   ;; \language output.LANG or
>   ;; \language LANG—which is equivalent to
>   ;; \language general.LANG or to the first two combined
>   (symbol-list-or-symbol?)
>   (_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.")
>
>
>   (let* ((correct-input (if (> (length arg) 2) #f #t))
>          (channel (if (= 2 (length arg)) ;if a channel is given,
>                       (car arg)    ;use it
>                       'general))     ;else apply to both
>          (language (cond ((= 1 (length arg)) (list-ref arg 0))
>                      ((= 2 (length arg)) (list-ref arg 1))))
>
>
> If correct-input is #f, language will be undefined.  You could add
> (else #f)
You’re right, that was an oversight on restructuring the code. A 
previous version had (else #f) here. I intended to replace the test in 
the following two if clauses by correct-input.
>          (input-lang (if language ;if input isn’t wrong
>                          language
>  'nederlands)) ;default
>
>
> The boolean value of #<unspecified> is ... #t, so input-lang will 
> select language if the input is not correct.  language will be 
> #<unspecified>.
>
>          (output-lang (if language
>                           language
>                           'english)))
>
> As above.
>
> Possibly you shouldn't bind the variables after correct-input unless 
> the input is correct.
I see – simply aborting the function (with a warning of course) instead 
of carefully reinstating the default values…
And you’re right, using { b } in the example also tests note name 
language without giving errors.
Attached a version with these changes incorporated, without user syntax 
changes for now.

Yours, Simon

define-languages.ly
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