From: Michael Heerdegen <michael_heerdegen@web.de>
To: Nicolas Petton <nicolas@petton.fr>
Cc: "Clément Pit--Claudel" <clement.pit@gmail.com>, emacs-devel@gnu.org
Subject: Re: [PATCH] Elpa: Pinpoint semantics of `seq-subseq' for streams
Date: Fri, 16 Sep 2016 00:30:28 +0200 [thread overview]
Message-ID: <87bmzoaj97.fsf@web.de> (raw)
In-Reply-To: <87mvj9ftb0.fsf@petton.fr> (Nicolas Petton's message of "Thu, 15 Sep 2016 10:42:11 +0200")
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Nicolas Petton <nicolas@petton.fr> writes:
> I agree, the patch is good as it is now, I'd like to have it
> installed.
Done.
FWIW, if you would like me to push this: I have implemented the sliding
window algorithm as suggested by John, but commented it out, and added a
(hopefully not too wordy) note why we raise an error for now for
negative indexes:
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From df5652f68fc0ca6730b3f830e805cf7e30e5615d Mon Sep 17 00:00:00 2001
From: Michael Heerdegen <michael_heerdegen@web.de>
Date: Fri, 16 Sep 2016 00:14:28 +0200
Subject: [PATCH] Add a comment to last change in stream.el and bump version
---
packages/stream/stream.el | 25 +++++++++++++++++++------
1 file changed, 19 insertions(+), 6 deletions(-)
diff --git a/packages/stream/stream.el b/packages/stream/stream.el
index 9954fc8..db00b0d 100644
--- a/packages/stream/stream.el
+++ b/packages/stream/stream.el
@@ -4,7 +4,7 @@
;; Author: Nicolas Petton <nicolas@petton.fr>
;; Keywords: stream, laziness, sequences
-;; Version: 2.2.1
+;; Version: 2.2.2
;; Package-Requires: ((emacs "25"))
;; Package: stream
@@ -237,11 +237,24 @@ START on. Both START and END must be non-negative. Since
streams are a delayed type of sequences, don't signal an error if
START or END are larger than the number of elements (the returned
stream will simply be accordingly shorter, or even empty)."
- (when (or (< start 0) (and end (< end 0)))
- (error "seq-subseq: only non-negative indexes allowed for streams"))
- (let ((stream-from-start (seq-drop stream start)))
- (if end (seq-take stream-from-start (- end start))
- stream-from-start)))
+ (if (or (< start 0) (and end (< end 0)))
+ ;; We could return something like this (for START and END < 0):
+ ;;
+ ;; (let ((cropped stream))
+ ;; (cl-dotimes (_ (- start)) (stream-pop cropped))
+ ;; (while (not (stream-empty-p cropped))
+ ;; (stream-pop stream)
+ ;; (stream-pop cropped))
+ ;; (seq-take stream (- end start)))
+ ;;
+ ;; but we are not sure whether advertising negative indexes is a good
+ ;; idea: this would potentially create a bunch of thrown away objects,
+ ;; and "searching from the end" might be better in most use cases. So
+ ;; we raise an error instead:
+ (error "seq-subseq: only non-negative indexes allowed for streams")
+ (let ((stream-from-start (seq-drop stream start)))
+ (if end (seq-take stream-from-start (- end start))
+ stream-from-start))))
(cl-defmethod seq-into-sequence ((stream stream))
"Convert STREAM into a sequence."
--
2.9.3
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Michael.
next prev parent reply other threads:[~2016-09-15 22:30 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-09-13 16:23 [PATCH] Elpa: Pinpoint semantics of `seq-subseq' for streams Michael Heerdegen
2016-09-13 18:02 ` Clément Pit--Claudel
2016-09-13 21:17 ` Michael Heerdegen
2016-09-14 1:24 ` Clément Pit--Claudel
2016-09-14 15:05 ` Michael Heerdegen
2016-09-14 23:26 ` Clément Pit--Claudel
2016-09-15 0:51 ` John Mastro
2016-09-15 2:00 ` Clément Pit--Claudel
2016-09-15 17:01 ` John Mastro
2016-09-15 21:07 ` Michael Heerdegen
2016-09-15 22:18 ` Clément Pit--Claudel
2016-09-15 22:28 ` Michael Heerdegen
2016-09-15 22:52 ` Clément Pit--Claudel
2016-09-15 0:58 ` Michael Heerdegen
2016-09-15 3:47 ` Clément Pit--Claudel
2016-09-15 8:42 ` Nicolas Petton
2016-09-15 22:30 ` Michael Heerdegen [this message]
2016-09-15 23:08 ` Nicolas Petton
2016-09-15 21:29 ` Michael Heerdegen
2016-09-14 1:28 ` John Wiegley
2016-09-14 15:15 ` Michael Heerdegen
2016-09-13 22:20 ` Nicolas Petton
2016-09-13 22:40 ` Michael Heerdegen
2016-09-14 8:25 ` Nicolas Petton
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