From: "Basil L. Contovounesios" <contovob@tcd.ie>
To: Alex Branham <alex.branham@gmail.com>
Cc: 33309@debbugs.gnu.org, Michael Albinus <michael.albinus@gmx.de>,
Stefan Monnier <monnier@IRO.UMontreal.CA>
Subject: bug#33309: Add flatten-list?
Date: Mon, 10 Dec 2018 22:42:14 +0000 [thread overview]
Message-ID: <87tvjl80mx.fsf@tcd.ie> (raw)
In-Reply-To: <87sgz5m98k.fsf@gmail.com> (Alex Branham's message of "Mon, 10 Dec 2018 14:12:43 -0600")
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[Sorry, Alex, for sending this to you twice - I accidentally made my
last message a narrow, rather than wide, reply.]
Alex Branham <alex.branham@gmail.com> writes:
> Thanks for the feedback, everyone.
Thanks for working on this.
> Here's a patch that implements `flatten-tree' which always returns a
> list and recurses into conses.
Given Emacs' recursive limitations, wouldn't an iterative implementation
be better? For instance, the following currently blows
max-specpdl-size:
(length (flatten-tree (make-list 800 nil)))
How about something like the following?
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diff --git a/lisp/subr.el b/lisp/subr.el
index f7eac75305..3fed3bc436 100644
--- a/lisp/subr.el
+++ b/lisp/subr.el
@@ -5453,10 +5453,15 @@ flatten-tree
This always returns a list containing all the elements of TREE.
\(flatten-tree \\='(1 (2 3 (4 5 (6))) 7))
=> (1 2 3 4 5 6 7)"
- (cond ((null tree) nil)
- ((consp tree) (append (flatten-tree (car tree))
- (flatten-tree (cdr tree))))
- (t (list tree))))
+ (let (elems)
+ (setq tree (list tree))
+ (while (let ((elem (pop tree)))
+ (cond ((consp elem)
+ (setq tree (cons (car elem) (cons (cdr elem) tree))))
+ (elem
+ (push elem elems)))
+ tree))
+ (nreverse elems)))
;; Technically, `flatten-list' is a misnomer, but we provide it here
;; for discoverability:
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--
Basil
next prev parent reply other threads:[~2018-12-10 22:42 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-07 19:46 bug#33309: Add flatten-list? Alex Branham
2018-11-07 20:36 ` Drew Adams
2018-11-07 21:19 ` Alex Branham
2018-12-10 8:44 ` Michael Albinus
2018-12-10 17:49 ` Stefan Monnier
2018-12-10 20:12 ` Alex Branham
2018-12-10 21:36 ` Stefan Monnier
2018-12-10 23:06 ` Alex Branham
2018-12-11 12:36 ` Stefan Monnier
2018-12-10 22:42 ` Basil L. Contovounesios [this message]
2018-12-10 23:17 ` Alex Branham
2018-12-10 23:26 ` Basil L. Contovounesios
2018-12-10 23:34 ` Stephen Berman
2018-12-11 8:21 ` Michael Albinus
2018-12-11 8:34 ` martin rudalics
2018-12-11 17:36 ` bug#33309: [PATCH] flatten-list Alex Branham
2018-12-11 20:11 ` Michael Albinus
2018-12-11 20:16 ` Alex Branham
2018-12-17 11:33 ` Michael Albinus
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