There's a find in Foldable: https://github.com/purescript/purescript-foldable-traversable/blob/master/src/Data/Foldable.purs#L96, isn't findIndex elemIndex ?

Or do these have different behavior from the Foldable versions?

Oh, of course! Thanks.

findIndex is different from elemIndex as it uses a predicate rather than equality. But now you mention it we have a duplicate Data.Array.elem, but a bad one as it doesn't use Eq. I'll close this, drop find, and submit a new PR that fixes these other issues.