#876: Length is not a good consumer
--------------------------------+-------------------------------------------
Reporter: ariep@… | Owner: simonpj
Type: bug | Status: new
Priority: lowest | Milestone: 7.6.2
Component: libraries/base | Version: 6.5
Keywords: length | Os: Linux
Architecture: x86 | Failure: Runtime performance bug
Difficulty: Unknown | Testcase: list003
Blockedby: | Blocking:
Related: |
--------------------------------+-------------------------------------------
Changes (by george.colpitts):
* failure: None/Unknown => Runtime performance bug
Comment:
I don't remember explicitly setting Type of failure to None/Unknown when I
added a keyword of length but it seems I did. I have now changed the
failure type to runtime performance bug. On ghc 7.4.1 the problem I see is
that the space usage of length is O(n) not O(1) in the size of the input,
perhaps this is a better summary of the bug. I'm assuming that this is
what "length is not a good consumer" means. This of course also slows down
execution speed. Given the preceding I'm not sure why priority is lowest.
{{{
*Main> length [0 .. (2^20)]
1048577
it :: Int
(0.03 secs, 42303644 bytes)
*Main> length [0 .. (2^30)]
1073741825
it :: Int
(23.08 secs, 42950370096 bytes)
*Main> 42950370096 / 42303644
1015.2877160180338
}}}
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/876#comment:20>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
_______________________________________________
Glasgow-haskell-bugs mailing list
Glasgow-haskell-bugs@haskell.org
http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
