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Consider strictness of unzip/unzipWith #162
Description
My personal intuition suggests that most instances should be "strict in the leaves, lazy in the spine" like the [] instance. However, most of them seem to be lazy all over the place.
NB: Data.Sequence.Seq actually needs its unzip to be lazy in the leaves in order to be lazy in the spine. If it tried to be strict in the leaves but lazy in the spine, it would end up being strict in part of the spine, which would break the abstraction barrier. sigh.
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treeowl commentedon Aug 22, 2021
Thinking about this a bit more, I wonder if it would actually make sense to offer several more unzipping methods, to get precisely the behavior you want.
I would expect all of them to be head-strict (
unzip _|_ = _|_), though that might be a tad confusing for a functor likeIdentity.We can offer sensible defaults of all of these except (as far as I can tell) lazy-spine/strict-separation for
Traversabletypes. I think that one type probably just requires too much human judgement to say what it means.