Re: tiny function

[David Kastrup]

Thomas Morley <address@hidden> writes:

> 2016-07-01 7:05 GMT+02:00 David Kastrup <address@hidden>:
>> Thomas Morley <address@hidden> writes:
>
>>> %% works:
>>> tstII =
>>> \with { instrumentName = "foo" shortInstrumentName = "foo" }
>>> \new Staff \tstII { r1 }
>>
>> Issue 4911 is supposed to harmonize this by stopping the second example
>> from working.  This makes it possible to recognize the syntax without
>> knowing the type of \tstII in advance (could be a music expression,
>> leading to completely different structure).
>
> I'm in two minds here.
> Hormonizing code is always preferable, but being able to spare the
> extra \with would be nice as well.

Why?  There are technical considerations underlying this change that are
also related to usability changes, like editors having a chance to
properly identify and indent parts of an expression.

It is not possible to let an argument-less scheme function work in the
same manner/syntax as a fixed context modification works right now.
Fixing that comes at a high cost, basically requiring special-casing
scheme functions in a similar vein as now music/event functions are
special-cased.  Which is something that makes it impossible to create
structures of music/event functions and other things.


> To join both while letting it recognizable I tried:
>
> #(defmacro-public define-with-function rest
>  `(define-syntax-function ly:context-mod? ,@rest))
>
> tstI =
> #(define-with-function ()() #{ \with { instrumentName = "-name-" } #})
>
> \new Staff \tstI { r1 }
>
> Doesn't work.
> A mistake somewhere or is it all rubbish?

Context mod functions are not special-cased.  If you write

(define my-music? (lambda (x) (ly:music? x)))
(define-syntax-function my-music? ...)

the result will stop working as a music function.  Similar for event
functions.  But at the current point of time, those are the only two
special-cased function types.  I want to decrease rather than increase
the number of special-cases here.

>>> %%(3)
>>> #(define (set-instrument-names-to-number-string nmbr mus)
>>>         (if (eq? (ly:music-property mus 'name) 'ContextSpeccedMusic)
>>>             (ly:music-set-property! mus 'property-operations
>>>               (list
>>>                 (list
>>>                   'assign
>>>                   'instrumentName
>>>                   (format #f "~a." nmbr))
>>>                 (list
>>>                   'assign
>>>                   'shortInstrumentName
>>>                   (format #f "~a." nmbr))))
>>>               mus)
>>>             mus)
>>>
>>> tst =
>>> #(define-music-function (nmbr mus)(number? ly:music?)
>>> (set-instrument-names-to-number-string nmbr mus))
>>>
>>> \tst #3 \new Staff { r1 }
>>
>> Hm.  At the current point of time, destructuring expression requires
>> Scheme programming.  And absorbing \new Staff into \tst #3 makes things
>> much less flexible (\context Staff = "..." just becomes impossible
>> then).
>
> Wasn't aware of this problem. Thanks spotting it.

No, you misunderstand.  This is not a problem with your code.  It's
rather a complaint that there is no reasonably better or more readable
way to write your code while keeping it working for a similarly large
number of use cases.

-- 
David Kastrup