Add intersperse

[i-am-the-slime]

Every once in a while, I find myself needing this.
Then I find this again. And then I go look it up here.

I don't know about the performance characteristics but I could translate the Haskell version into PS.

[i-am-the-slime]

Maybe it doesn't belong here, but to Array and friends?

[hdgarrood]

I agree, I’ve wanted this too, and using intercalate is less than ideal, not only because it’s slower, but also because I find it’s surprisingly hard to work out how to get the types to line up to get it to do what I want. I think adding monomorphic forall a. a -> T a -> T a functions for T = Array, List, etc would be the way to go. Foldable doesn’t quite seem appropriate because it doesn’t really give you a good way of preserving structure; I think an implementation in terms of Foldable would have to rely on a Semigroup instance which does concatenation.

[hdgarrood]

I'll close this as I think it's covered by purescript/purescript-arrays#15 and purescript/purescript-lists#132, and we wouldn't put these functions in this library.