Re: Direction operators in event-function

[Urs Liska]

Am 21.10.2018 um 17:52 schrieb David Kastrup:

With explicit I refer to a direction explicitly assigned, either
thorugh ^/_ or an \override like \slurUp etc. If I call my function
with ^\propagate-direction there is an explicit direction in place
while the event-function is called, isn't it?

No.  I have no idea how you think direction operators work.  They don't
magically change the meaning of expressions such as

#{ -\markup #text #}

Expressions are evaluated from inside to outside, like with basically
every computer language implementing operators.

If OTOH I call it with -\propagate-direction or without an operator
the direction will only be generated/calculated at some later point,
depending on the layout algorithms.  Is that correct or am I missing
something?

You are missing something.  -postevent leaves postevent as-is,
^postevent sets it direction to #UP , _postevent sets it direction to
#DOWN .  Before it can do anything with that postevent, the postevent
has to be _there_ in the first place, like it is when being returned by
an event function.

Well, this explains my misunderstanding, and there's not much sense in trying to clarify all the follow-up misunderstandings. I mistook the direction operators to work like arguments passing information into the event-function which would then transparently be used inside.

If I have a fresh mind tomorrow I'll see how I can use this new understanding to solve my tasks ...

Urs