#9339: last is not a good consumer -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: | Version: 7.8.3 libraries/base | Keywords: Resolution: | Operating System: Unknown/Multiple Differential Revisions: | Type of failure: Runtime Architecture: | performance bug Unknown/Multiple | Test Case: Difficulty: Unknown | Blocking: Blocked By: | Related Tickets: | -------------------------------------+------------------------------------- Comment (by dfeuer): Replying to [comment:3 nomeata]:
That looks wonderful. Is it certain to be changed to a foldl' in cases where it doesn't fuse?
Hopefully not. `foldl'` would force the accumulator, which we do *not* want here (otherwise the `undefined` would be forced, or `last [undefined, 1]` would not work).
Yes, you're right. I got mixed up a bit.
I didn’t do further testing with that idea, it just crossed my mind. It maybe the that this implementation is only good when fusing works – would you mind trying to find out?
I don't have anything beyond 7.8.3, and on 7.8.3 your code doesn't fuse. Could you maybe try it? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9339#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler