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

[Max Bolingbroke]

On 16 October 2010 12:16, Roman Leshchinskiy <rl at cse.unsw.edu.au> 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"
:-)

Max