Re: Discussion: Add total indexing function to Data.Sequence

29 May 2016

      How about (!?) like Data.Vector?

On Sun, May 29, 2016 at 5:21 PM, David Feuer  wrote:
...
Data.Sequence offers
index :: Seq a -> Int -> a
which throws an error if the index is out of range. I'd like to add
something like
indexMay :: Seq a -> Int -> Maybe a
Aside from the safety factor, indexMay would offer a way to ensure the
indexing occurs at a particular time. Much like Data.Vector.indexM,
this can help prevent memory leaks. In fact, an analogue of indexM can
be implemented in terms of indexMay:
indexM :: Applicative m => Seq a -> Int -> m a
indexM xs i = case xs `indexMay` i of
  Nothing -> error "indexM: index out of range"
  Just x -> pure x