Didn’t look at the core yet, but this might be a case of non-linear recursion where an arity analysis in insufficient to get good code for a left fold, see 5.1.1 in http://pp.ipd.kit.edu/uploads/publikationen/breitner14callarity.pdf.
I can have a closer look later. Can you, with these examples, please always include one complete self-contained file? Otherwise there is a risk
#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 dfeuer): Replying to [comment:22 nomeata]: that I might be testing with the wrong version of inits/scanl'/whatever. I assume you are on GHC HEAD? I've attached a complete, self-contained test case. As I mentioned in an email, you should keep a close eye on RAM usage or run this program with heap limits set if you don't want to crash your computer. If this is an arity analysis problem that's too hard to fix, we can work around it by writing `inits xs = don'tFuse . map toListQ . scanl' snocQ emptyQ` to ensure that `inits` doesn't fuse on the problematic (and, in fact, rather unimportant) side. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9345#comment:23 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler