I think the "official" version could be implemented with a lazy pattern match and it'd be the same as yours, no?

Cheers,
Vanessa

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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