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

[Roman Leshchinskiy]

On 16/10/2010, at 12:36, Max Bolingbroke wrote:

> 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"
> :-)

I suspect the easiest way to achieve this is to expand the set of GHC-optimisable things until it includes eta :-)

Roman