#9345: Data.List.inits is extremely slow -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: libraries/base | Version: 7.8.3 Keywords: | Differential Revisions: Operating System: Unknown/Multiple | Architecture: Type of failure: Runtime | Unknown/Multiple performance bug | Difficulty: Easy (less Test Case: | than 1 hour) Blocking: | Blocked By: | Related Tickets: -------------------------------------+------------------------------------- As discussed on libraries@haskell.org, `Data.List.inits` is extremely slow (try running `print $ length $ inits [1..100000]` if you don't believe me). As discussed, there are at least two reasonable fixes. One of them (named `initsR` in the attached) is a one-liner and gives very good performance in general, but poor performance in certain cases that may or may not appear in real code. The other (named `initsQ` in the attached) is slightly more complex and slightly slower in general, but its performance appears to be robust. I would personally lean toward `initsQ` for `Data.List`. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9345 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler