Remember that GHC doesn’t inline recursive things (such as `cyc`).
Also, I don’t think your `cycle` is a good consumer: To inline it, you need to know that its argument is a `:`. But to make it a good consumer,
#9398: Data.List.cycle is not a good producer -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: Type: bug | Status: new Priority: normal | 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:3 nomeata]: the argument needs to be of the shape `build ...`. I suppose I should (try to) find a way to rewrite it to another form if it doesn't get eaten by foldr. I'm not understanding your concern about the consumption side. `cyc` isn't inlined, but the enclosing `cycle` is. Shouldn't that be good enough to allow the `foldr` in `cycle'` to fuse with a `build` or `augment` in `xs`? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9398#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler