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Re: Passing music objects into scheme functions

From: David Kastrup
Subject: Re: Passing music objects into scheme functions
Date: Mon, 14 Aug 2017 20:15:42 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/26.0.50 (gnu/linux)

Charles Winston <address@hidden> writes:

>> On Aug 14, 2017, at 1:34 PM, David Kastrup <address@hidden> wrote:
>> David Kastrup <address@hidden> writes:
>>> Charles Winston <address@hidden> writes:
>>>>> On Aug 14, 2017, at 1:20 PM, David Kastrup <address@hidden> wrote:
>>>>> Charles Winston <address@hidden> writes:
>>>>>> Here is the function inside chord-name.scm
>>>>>> ;; chordmode-to-exceptions
>>>>>> (define-safe-public (chordmode-to-exceptions chord markup)
>>>>>> "Transform event-chord entered in chord mode to alist
>>>>>> entry in chordSemanticsNameExceptions list
>>>>>> "
>>>>>> (define (is-semantics-event? x)
>>>>>>   (ly:in-event-class? x 'chord-semantics-event))
>>>>> Event classes are for stream events, not for music expressions.
>>>>>> (define (get-semantics chord)
>>>>>>   (let* ((elts (ly:music-property chord 'elements))
>>>>>>          (semantics-event (filter is-semantics-event? elts))
>>>>>>          (semantics-list (ly:event-property semantics-event 
>>>>>> 'chord-semantics)))
>>>>> ly:event-property is for stream events, not for music expressions.
>>>>>>     semantics-list))
>>>>>> (list (cons (get-semantics chord) markup)))
>>>>> Stream events are generated from music expressions during iteration of
>>>>> music expressions (the interpretation phase making use of engravers
>>>>> etc).
>>>> I believe these actually are stream events.
>>> It doesn't matter what you believe.  After
>>>> chordVar = \chordmode { c1:m7 }
>>>> markupVar = \markup { “min7” }
>>>> #(chordmode-to-exceptions chordVar markupVar)
>>> chordVar most certainly is a music expression rather than a stream
>>> event.  And chordmode-to-exceptions is a confused mess that sometimes
>>> calls ly:music-property and sometimes ly:event-property on its
>>> constituents.  There is no input (apart from empty chords) that it will
>>> process sensibly unless your branch messes up \chordmode completely and
>>> generates a mishmash of stream events and music expressions.
>> Ok, that was quite uncalled for.  I apologize for the pigheaded way I
>> expressed myself here.
> I know that chordVar isn’t a stream event. I was saying
> chord-semantics-event is. Anyway this is what I’m trying to do:
> Extract the elements property from the chord parameter, thats when I
> call ly:music-property. Then from the elements, I want to find the
> element which is a chord-semantics-event. I do this with the function
> is-semantics-event?. This stream event is something I’ve defined as a
> part of my summer of code project and has worked for naming chords
> using semantics.

Well, I am afraid you will have to change it to a music expression then.
Stream events do not belong outside of iteration.  Functions like
ly:in-event-class presume working with stream events, and with good

When a music event is converted to a stream event in the course of
iteration (not all are), any 'elements in it are converted from music to
stream event as well.

David Kastrup

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