<< Back to previous view

[CLJ-1497] sequence with transducers realizes n+2 elements Created: 08/Aug/14  Updated: 08/Aug/14  Resolved: 08/Aug/14

Status: Closed
Project: Clojure
Component/s: None
Affects Version/s: Release 1.7
Fix Version/s: Release 1.7

Type: Defect Priority: Major
Reporter: Nicola Mometto Assignee: Unassigned
Resolution: Completed Votes: 0
Labels: None

Attachments: File clj-1497.diff     File clj-1497v2.diff    
Approval: Ok

 Description   

The first element is realized at creation time:

user=> (def a (sequence (take 2) (map #(do (println (str "~" %)) %) (iterate inc 1))))
~1
#'user/a

Fully realizing the sequence realizes the other n-1 elements, and 2 more:

user=> a
(~2
~3
1 ~4
2)

Compare with version using seq operations:

user=> (def a (sequence (take 2 (map #(do (println (str "~" %)) %) (iterate inc 1)))))
#'user/a
user=> a
(~1
~2
1 2)

Transduce also doesn't seem to exhibit this issue:

user=> (def a (transduce (take 2) conj [] (map #(do (println (str "~" %)) %) (iterate inc 1))))
~1
~2
#'user/a
user=> a
[1 2]


 Comments   
Comment by Alex Miller [ 08/Aug/14 10:02 AM ]

Patch attached that improves the issue - will now only realize n+1 elements.

Comment by Nicola Mometto [ 08/Aug/14 10:16 AM ]

Nice, I added a commit on top of yours to delay the realization of the first element of the lazyseq to the first .next call instead of on SeqIteration creation

Comment by Alex Miller [ 08/Aug/14 11:12 AM ]

Fixed by Rich directly, not by patch.

Generated at Sun May 19 14:12:38 CDT 2019 using JIRA 4.4#649-r158309.