Add unsnoc #94
Add unsnoc #94
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👍 Looks good to me, thanks! |
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| -- | Running time: `O(2n)` | ||
| unsnoc :: forall a. List a -> Maybe { init :: List a, last :: a } | ||
| unsnoc xs = { init: _, last: _ } <$> init xs <*> last xs |
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Actually, can we do this in a single pass? Otherwise, the user doesn't gain anything over using the functions separately.
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My motivation for adding it was that it makes pattern-matching cleaner. Otherwise, you have to do separate Maybe checks for both init and last. But sure, I'd be happy to optimize it. 😃
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| unsnoc :: forall a. List a -> Maybe { init :: List a, last :: a } | ||
| unsnoc lst = unsnocHelper lst Nil <#> \h -> { init: reverse h.revInit, last: h.last } | ||
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| unsnocHelper :: forall a. List a -> List a -> Maybe { revInit :: List a, last :: a } |
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Could you please move this under a where? It could be called go - it's not the best name, but it's consistent with the other implementations here.
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Sure! The main reason I split it off was concerns about performance – I figured that redefining go on every call to unsnoc was wasteful. But I don't know much about that, so I'll take your advice.
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I don't know the extent to which JS engines optimize under functions, but I'd say it's better to be consistent at this point.
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👍 Thanks! |
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