Hi Stephen,
On 2 January 2011 13:35, Stephen Tetley
Can a lazy cons be implemented for (infinite) Streams in the Stream-Fusion style?
I made a mailing list post about almost exactly this issue a while ago (http://www.mail-archive.com/haskell-cafe@haskell.org/msg82981.html). There was no really nice solution offered: I think the best you can do is define your stream operations with a lazy pattern match using my "eta" trick from that post: eta stream = Stream (case stream of Stream s _ -> unsafeCoerce s :: ()) (case stream of Stream _ step -> unsafeCoerce step) Then instead of writing: f (Stream x y) = ... Write: f (eta -> Stream x y) = ... (This is necessary because lazy pattern matches on existential data constructors using ~ cannot even be expressed in System FC, so it is unclear how GHC could implement them). Cheers, Max