Re: Issue 3918: Add \alternatingTimeSignatures (issue 97110045)

[Paul Morris]

David Kastrup wrote
>>
>> Assuming we would want to support stencils as well as markups, we'd need
>> a
>> new type predicate: 
>>
>> markup-or-stencil?
>>
>> And if it is to be as flexible as a \tweak, then it should also support
>> procedures (i.e. that return a stencil).
> 
> I don't think it makes a lot of sense to support procedures as then so
> many internals shine through that the abstraction is basically gone.
> I am already unconvinced about stencils for that reason.
> 
>> So we'd need:
>>
>> markup-or-stencil-or-procedure?
> 
> markup-or-stencil-or-procedure-or-false? ...
> 
> We don't do this elsewhere.

Good point about needing false to cover the full range of \tweak inputs for
stencils.  Let me try to make the case that such a long and unprecedented
type predicate might actually make sense here by comparing two stories we
could present to users.

1. "To do A with markups you have to use B, but to do A with stencils or
procedures you have to use C."

2. "To do A you can always use B.  It works with markups, stencils, or
procedures."


Or to put it another way:

1. "Here's a shortcut for tweaking/replacing a stencil.  It only accepts
markups.  If you want to tweak/replace a stencil with another stencil you
have to wrap your stencil in a \markup \stencil first (or just use the
non-shortcut form).  If you want to tweak/replace a stencil with a procedure
then you have to use the non-shortcut form."

2. "Here's a shortcut for tweaking/replacing a stencil.  It works just like
the non-shortcut form for tweaking/replacing a stencil except that it can
also accept markups."  


As a user I prefer 2 because I only have to learn one command that will work
with anything (reasonable) that I throw at it.  If I only ever use markups
then everything is the same as with 1 (and I don't have to see any
additional internals shining through), but if at some point I want to use
stencils or procedures then I don't have to learn a new way to do it.


So maybe the question is whether we're talking about a general shortcut for
tweaking stencils, or a new command for tweaking stencils with markups.  If
it is only for markups then maybe the name should be less general to
indicate this specific use?  Something like \substituteMarkup ?  

Cheers,
-Paul



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