#9345: Data.List.inits is extremely slow -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: Type: bug | Status: new Priority: high | Milestone: 7.8.4 Component: | Version: 7.8.3 libraries/base | Keywords: Resolution: | Architecture: Unknown/Multiple Operating System: | Difficulty: Easy (less than 1 Unknown/Multiple | hour) Type of failure: Runtime | Blocked By: performance bug | Related Tickets: Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Comment (by nomeata):
This doesn't seem to affect the problem, however.
Yes, I don’t think the problem in this particular case lies with init per se. I think it’s more like concat, but only when part of the recursion (the `c` above) is not inlined. That might also be what you observe.
I am curious if there is a way to manually force whatever's getting the wrong arity to get the right one
Not with list fusion as we have it right now, I think. It should work with https://github.com/takano-akio/ww-fusion (which I should follow up on again). I don’t think a rule for `concat (inits)` is worth it, but it may help us understand the problem better. I wonder if maybe the rule for `concat` can be rewritten so that the resulting recursion is nicer, but I don’t see it right now (but I’m too jetlagged to think anyways). -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9345#comment:26 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler