deleteLookup :: Int -> Seq a -> Maybe (a, Seq a)
deleteLookup n q = case Seq.splitAt n q of
(ql, qr) -> case Seq.viewl qr of
Seq.EmptyL -> Nothing
(Seq.:<) a qr' -> Just (a, ql <> qr')
If it were written natively, it'd probably use some of the machinery from
splitAt.
On 13:25, Sat, Dec 28, 2019 David Feuer Data.Sequence offers deleteAt :: Int -> Seq a -> Seq a which deletes the element at the given index. Today, I ran into a
situation where I wanted to know what was deleted. deleteLookup :: Int -> Seq a -> Maybe (a, Seq a) The closest thing I can find in `containers` is in Data.Map: updateLookupWithKey :: Ord k => (k -> a -> Maybe a) -> k -> Map k a
-> (Maybe a,Map k a) Unfortunately, that function is ugly and strange. A better one, whose
name I can't guess at the moment: flabbergast :: (a -> (b, Maybe a)) -> Int -> Seq a -> Maybe (b, Seq a) where a Nothing result means the index was out of bounds. There's also
a potential flabbergastF :: Functor f => (a -> f (Maybe a)) -> Int -> Seq a ->
Maybe (f (Seq a)) I'm not sure if flabbergast can be made as fast as deleteLookup, so
it's possible we may want both. Any opinions?
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