[Haskell-cafe] Is unfoldr too strict?

[Isaac Elliott]

Yep, a lazy pattern match gets you the same benefit.

On Tue, 11 Dec. 2018, 7:50 pm Vanessa McHale, <vanessa.mchale at iohk.io>
wrote:

> I think the "official" version could be implemented with a lazy pattern
> match and it'd be the same as yours, no?
>
> Cheers,
> Vanessa
> On 12/11/18 12:55 AM, Isaac Elliott wrote:
>
> I was reading this article
> https://wiki.haskell.org/Correctness_of_short_cut_fusion on the Haskell
> wiki. It presents an example (2.1.2) where destroy/unfoldr fusion behaves
> oddly. If I use a lazier definition of unfoldr, then this problem goes away:
>
> unfoldr :: (b -> Maybe (a, b)) -> b -> [a]
>> unfoldr f b =
>>   case f b of
>>     Nothing -> []
>>     Just z -> fst z : unfoldr f (snd z)
>
>
> Does this mean unfoldr is 'too strict'? Or is there a good reason for not
> writing it this way (performance, perhaps?)
>
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