Re: Issue 5740: Add \post to defer context actions to end of time step (issue 581600043 by address@hidden)

[benko . pal]

On 2020/02/06 14:29:55, Dan Eble wrote:
> The reviewers are turning the first question I asked around and asking
it back
> to me.  I don't know if this is useful without other stuff I've been
working on.
>  That's why I've posted it for review.  I thought that you (well,
mainly I
> thought that David K.) might know of some corner of LilyPond where
delaying a
> \set (or similar thing) until the end of the current time step would
be useful.

I remember very faintly (incorrectly???) that many years ago I had a
problem of
doing something at the last point in time, as points of time could be
deduced only
from the beginning of durations, not from the end of those; if that is
so (or if
there are cases when determining a point of time is more natural as the
end of a
duration than as the beginning of another one), \post is definitely
useful.

Another conceivable meaning is, used together with \once:
"tweak something, and when it finished, tweak something else"
(may perhaps be useful when pasting music from tiny fragments or using a
complex
hierarchy of music functions).
This meaning would perhaps be
- expressed better with \next (or \then? is it reserved?) than \post;
- supported better if \once and \post could be iterated like if .. else
if .. else,
i.e. if

\once \set <tweak1> \post \once \set <tweak2> \post \set <tweak3>
<note1> <note2> ...

meant

\set <tweak1>
<note1>
\set <tweak2>
<note2>
\set <tweak3>
...


but as the new set-once-post.ly regtest shows, this is not how it works
with this patch.

https://codereview.appspot.com/581600043/