Re: simple scheme function #{ $note #}

[David Kastrup]

Aaron Hill <address@hidden> writes:

> On 2018-05-11 14:17, David Kastrup wrote:
>> Aaron Hill <address@hidden> writes:
>>> The error message reads pretty clearly, though.  The result of a music
>>> function cannot be a single NOTENAME_PITCH.
>>
>> The result of a music function cannot be a pitch, period.  It has to be
>> a music expression.  A pitch is not a music expression.
>
> I think we are in violent agreement here.  It is going to be pointless
> to nitpick details that are likely irrelevant and off-topic.  So in an
> effort to circle back to summarize and address the original
> question...
>
> A music function must evaluate to a music expression.
>
> The reason why #{ $p #} does not work as the body of a music function
> is that it will only evaluate to a pitch not a note, and that pitch by
> itself is not enough to create a music expression.

Wrong again.  There is no such thing as a "pitch by itself" in Scheme.
A pitch is not a deficient music expression, rather it is not a music
expression at all.  It's like saying a character by itself is not enough
to create a string, as if two characters by itself would create a
string.  Strings are not the same as characters of any count.

Strings are a separate data structure from characters.  You can place
characters in other data structures.  You can certainly also form
one-character strings.

(make-music 'NoteEvent 'pitch #{ c' #})

is a music expression a music function can return (it's deficient for a
number of unchanged uses in that it is lacking a duration but you can
add durations afterwards if you want to with different music functions).

Two pitches are not enough to create a music expression.  Ten pitches
aren't.  If you want to create a music expression, you need to create a
music expression, like using make-music.  Or use some #{ ... #}
construct recognized as producing music.

> #{ $p 4 #} works because a pitch followed by a duration clearly
> defines a note, which is enough to form a music expression.

#{ $p #} #{ 4 #} is a pitch followed by a duration and does not form a
music expression.  The music expression is created by specific forms of
the #{ ... #} syntax.

-- 
David Kastrup