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Re: [Emacs-diffs] master 387e1e1: New version of `seq-let' based on a pc
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From: |
Nicolas Petton |
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Subject: |
Re: [Emacs-diffs] master 387e1e1: New version of `seq-let' based on a pcase pattern |
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Date: |
Mon, 11 May 2015 15:42:39 +0200 |
Stefan Monnier writes:
>> + (pcase-defmacro seq (bindings)
>> + `(and ,@(seq--make-pcase-bindings bindings)))
>
> If you put a docstring in there, it will appear in "C-h f pcase RET", so
> you can use it to document the particular format you support.
Great, I'll do that.
> Also I see the following problems:
> - You only accept the form (seq <binding>) rather than (seq <binding1>
> <binding2> ...), so typical cases will have to use (seq (a b)) instead
> (seq a b).
Yes. My idea of it was that you bind a sequence like the following:
(seq [a b [c d]])
Or did you have something else in mind?
> - The above pcase pattern doesn't check that it's indeed a `seq'.
> You should add a (pred seq-p). It will automatically be optimized
> away in `pcase-let', but is indispensable for the `pcase' situation to
> do the right thing.
Ok, I'll do that.
>
>> +(defun seq--make-pcase-bindings (args &optional bindings nested-indexes)
> [...]
>> + (seq-doseq (name args)
>> + (unless rest-marker
>> + (pcase name
>> + ((pred seq-p)
>
> IIUC, this means that (pcase-let (((seq a (seq b c)) <obj>)) <body>)
> will bind the `seq' variable to the first element of the nested sequence
> (and `a' to the second and `b' to the third), whereas I think it should
> bind `b' to the first element of the nested sequence (which is what
> would happen if you simply removed this branch of this `pcase').
> I think removing this case will also remove the need for
> seq--nested-elt.
But then how can I have `seq-let' work the way it did until now? For
instance:
(seq-let [a [b [c]]] my-vector
...)
>> + (push `(app (seq--reverse-args #'seq--nested-elt
>> + (reverse (cons ,index
>> ',nested-indexes)))
>> + ,name)
>
> This reverse plus seq--reverse-args business seems
> hideously inefficient. Why do you need that?
because of the way the `app' pattern works. Or maybe I'm missing
something?
Nico
--
Nicolas Petton
http://nicolas-petton.fr
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