Allow for result arg in seq-doseq ?

Allow for result arg in seq-doseq ?

[Tino Calancha]

Dear Nico,

Currently seq-doseq unconditionally returns the input sequence.
Do you think might be useful to allow for an arg RESULT in the SPEC
as `dolist' does?

I mean something as follows:

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
diff --git a/lisp/emacs-lisp/seq.el b/lisp/emacs-lisp/seq.el
index e5004f8..109f547 100644
--- a/lisp/emacs-lisp/seq.el
+++ b/lisp/emacs-lisp/seq.el
@@ -62,14 +62,19 @@
  (defmacro seq-doseq (spec &rest body)
    "Loop over a sequence.
  Evaluate BODY with VAR bound to each element of SEQUENCE, in turn.
+Return RESULT if non-nil, otherwise return SEQUENCE.

  Similar to `dolist' but can be applied to lists, strings, and vectors.

-\(fn (VAR SEQUENCE) BODY...)"
+\(fn (VAR SEQUENCE [RESULT]) BODY...)"
    (declare (indent 1) (debug ((symbolp form &optional form) body)))
-  `(seq-do (lambda (,(car spec))
-             ,@body)
-           ,(cadr spec)))
+  `(progn
+     (seq-do (lambda (,(car spec))
+               ,@body)
+             ,(cadr spec))
+     ,(if (cddr spec)
+          (car (cddr spec))
+        (cadr spec))))

  (pcase-defmacro seq (&rest patterns)
    "Build a `pcase' pattern that matches elements of SEQUENCE.
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

In GNU Emacs 25.1.50 (x86_64-pc-linux-gnu, GTK+ Version 3.20.6)
  of 2016-08-07
Repository revision: b593ea1f9b7068c03fe6527a3cb6d5e1b2cd9736

Re: Allow for result arg in seq-doseq ?

[Nicolas Petton]

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Tino Calancha <tino.calancha@gmail.com> writes:

> Dear Nico,

Hi Tino,

> Currently seq-doseq unconditionally returns the input sequence.
> Do you think might be useful to allow for an arg RESULT in the SPEC
> as `dolist' does?

IIRC the first version was like that, but for a forgotten reason, Stefan
(in the Cc) thought that the RESULT arg was useless (I myself never use
it in `dolist').

I am not opposed to adding it back though.

Cheers,
Nico

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Re: Allow for result arg in seq-doseq ?

[Tino Calancha]

On Mon, 8 Aug 2016, Nicolas Petton wrote:

> IIRC the first version was like that, but for a forgotten reason, Stefan
> (in the Cc) thought that the RESULT arg was useless (I myself never use
> it in `dolist').
>
> I am not opposed to adding it back though.
Hi Nico,
To be honest i don't use RESULT on dolist either :-)

My weak motivation to add this is just that i 'dolist'
and 'seq-doseq' would be more similar.
Anyway, even allowing RESULT in 'seq-doseq' they will differ on the
return value when RESULT is missing:
* dolist return nil
* seq-doseq return sequence.

Regards,
Tino

Re: Allow for result arg in seq-doseq ?

[Stefan Monnier]

>> IIRC the first version was like that, but for a forgotten reason, Stefan
>> (in the Cc) thought that the RESULT arg was useless (I myself never use
>> it in `dolist').
>> 
>> I am not opposed to adding it back though.
> To be honest i don't use RESULT on dolist either :-)

FWIW, I'd favor for seq-doseq to return nil, to really discourage the
use of its output (which tends to hide the use and its corresponding
side-effects).


        Stefan

Re: Allow for result arg in seq-doseq ?

[Tino Calancha]

On Mon, 8 Aug 2016, Stefan Monnier wrote:

> FWIW, I'd favor for seq-doseq to return nil, to really discourage the
> use of its output (which tends to hide the use and its corresponding
> side-effects).
I agree.