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More laws and defaults #50

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treeowl opened this issue Nov 30, 2019 · 0 comments
Open

More laws and defaults #50

treeowl opened this issue Nov 30, 2019 · 0 comments

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@treeowl
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treeowl commented Nov 30, 2019

I think we can strengthen the

wither (pure . f) = pure . mapMaybe f

law added in #29:

wither f = fmap (mapMaybe id) . traverse f

It seems we should have also the law

mapMaybe f = runIdentity . wither (Identity . f)

These laws suggest a default implementation for wither and also a mapMaybeDefault function.
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