Foldable instance for Vector uses slow default implementations for many methods

[mgsloan]

The current definition is

instance Foldable.Foldable Vector where
  {-# INLINE foldr #-}
  foldr = foldr

  {-# INLINE foldl #-}
  foldl = foldl

  {-# INLINE foldr1 #-}
  foldr1 = foldr1

  {-# INLINE foldl1 #-}
  foldl1 = foldl1

The problem with this is that there are many other Foldable operations that have Vector versions which are much faster than the default implementations. Sometimes Vector even offers an asymptotically superior version, such as length, which has an O(n) default implementation, whereas Vector has a O(1) operation for this.

I would open a PR, but was dissuaded by the pile of existing ones.

[winterland1989]

Please go ahead, this is clearly an optimazation which won't break any API, who is the maintainer now? Please make a judgement ; )

[Shimuuar]

who is the maintainer now?

I'd love to know answer to this question.

[dolio]

The core libraries committee is the official maintainer, and they delegate mostly to me.

If someone wants to implement this, it sounds like a good idea to me.

[Shimuuar]

Well judging by number of open pull requests and commit history there isn't enough manpower to maintain vector properly.

[cartazio]

could someone roll a wee benchmark to validate switching Data.Vector and suchlike to this?

Relatedly: I presume we can only provide a Foldable instance for boxed vectors right?

[dolio]

I implemented this. And yes, it's only for boxed vectors (Foldable could be implemented for unboxed vectors, but only by packing the dictionary in the type).