Re: [Haskell-cafe] Eta-expansion and existentials (or: types destroy my laziness)

17 Oct 2010


      On 16/10/2010, at 12:36, Max Bolingbroke wrote:
...
On 16 October 2010 12:16, Roman Leshchinskiy  wrote:
...
eta :: Stream a -> Stream a
eta s = Stream s next
  where
    next (Stream s next') = case next' s of
                              Just (x,s') -> Just (x,Stream s' next')
                              Nothing     -> Nothing
Making GHC optimise stream code involving eta properly is hard :-)
Good point, I don't exactly mean non-recursive for requirement 3) then
- I mean an adjective with a fuzzier definition like "GHC-optimisable"
:-)
I suspect the easiest way to achieve this is to expand the set of GHC-optimisable things until it includes eta :-)

Roman