On Dec 14, 2013, at 9:35 AM, David Kastrup <d...@gnu.org> wrote:
> "Keith OHara" <k-ohara5...@oco.net> writes:
>
>> On Fri, 13 Dec 2013 23:05:49 -0800, David Kastrup <d...@gnu.org> wrote:
>>
>>> That does not make sense. If you want call-once behavior, you can just
>>> use a callback.
>>
>> At the moment, the decision on whether to preserve the callback
>> pointer in the grob property, or fill the property with the returned
>> value, depends on the method used to request the property,
>> get_pure_property() versus get_property(). A callback would be called
>> multiple times (and it would have to support the unpure-pure calling
>> convention).
>>
>> The information of whether the callback is providing a value that
>> /should/ be kept as final is better stored in the Grob itself, so I am
>> thinking of ways to reorganize.
>>
>> The way stencil callbacks are evaluated now is interesting. The
>> stencil callback itself is a simple callback, but when the layout
>> engine wants to know the size of a stencil it does
>> get_pure_property("Y-extent"). Y-extent property is set to either
>> execute the stencil callback, or estimate a height without building
>> the final stencil, as appropriate for each Grob.
>
> If you are thinking of reorganizing: the current state is a mess.
> I still have not figured out what ly:make-simple-closure is supposed to
> do.
ly:make-simple-closure delays evaluation of its parts until looked up.
It is exactly the same as a lambda function.
I don’t think anyone actually uses them anymore - probably can be retired.
>
> Most of the contortions seem focused about when or when not and how to
> pass begin/end columns. It would seem to make sense to turn them into
> dynamic parameters *begin* *end* that you can then query with (*begin*)
> and (*end*). If (*begin*) returns ##f, we can assume being in a pure
> calculation.
>
> That would seem to get rid of most of the current interface
> complications.
I can see the utility of having one function instead of two for these things.
The current pure and non-pure functions are often wrappers around a single
internal function that has a bool parameter called “pure”, so this would
eliminate the need for the wrapper functions.
Cheers,
MS
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