mapAccumL and variants

In Data.List, there is a function that maps over a collection while building an accumulator:

mapAccumL :: Traversable t => (a -> b -> (a, c)) -> a -> t b -> (a, t c)

Specialized to `Array`, this would be:

mapAccumL :: (a -> b -> (a, c)) -> a -> Array b -> (a, Array c)

This is basically a combination of `foldl` and `map`. There is a less expressive variant of this where the accumulator is a `Monoid` and you do not inspect it (a comparison to the contrast between `Writer` and `State` is apt here). This variant looks like this:

mapAccumMonoid :: Monoid a => (b -> (a, c)) -> Array b -> (a, Array c)

I use this function somewhat often. I've thought about adding it to `primitive`, but I'm going to just add it to contiguous for the time being. Just wanted to get these thoughts written down somewhere.