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bug#47261: Fwd: bug#47261: Destructuring with Pcase without assigning va
From: |
Earl Hyatt |
Subject: |
bug#47261: Fwd: bug#47261: Destructuring with Pcase without assigning values |
Date: |
Mon, 19 Apr 2021 22:06:51 +0000 |
For the record, I am forwarding this reply to the bug tracker. I forgot
to send the original message to the tracker.
-------- Forwarded Message --------
Subject: Re: bug#47261: Destructuring with Pcase without assigning values
Date: Sat, 17 Apr 2021 18:50:10 -0400
From: Okam <okamsn@protonmail.com>
To: Stefan Monnier <monnier@iro.umontreal.ca>
On 4/16/21 11:22 PM, Stefan Monnier wrote:
>
>>> The `pcase` macro itself uses this function, so it should hopefully be
>>> "good enough", but let me know if it's causing you trouble.
>> This seems to work well for my use case. Thank you for making this change.
>
> You're welcome. It was actually a good change for the code's
> readability as well.
>
>> Are the variables always given in the order that they appear in the
>> pattern?
>
> I don't know. Why? >
>> If not, is finding elements of the form "(\, SYMBOL)" enough to
>> identify variables in a Pcase pattern?
>
> No. , is not even one of the core pcase patterns, it's only something
> used within the ` pattern (which is not a core pattern either; it is
> defined via `pcase-defmacro`).
>
>
> Stefan
>
In the `cl-loop`-like macro that I am writing, things are currently set
up so that variables being assigned values in accumulation clauses can
be automatically used as the return value of the macro.
;; => ((1 3 5) (2 4 6))
(loopy (flag pcase)
(list i '((1 2) (3 4) (5 6)))
(collect `(,a ,b) i))
This behavior requires finding the variables in the correct order.
The getting of the variables used ("a" and "b" above) can be done when
using the new `pcase-compile-pattern`, if the variables are fed to the
CODEGEN argument in the order that they are written, or I can try to
find them manually, if possible.
If neither are possible, then I will just remove this behavior.
Thank you.