Re: [Haskell-cafe] HXT and types in Control.Arrow.ArrowTree

Robert Vollmert wrote:

In short, I'm constantly running into what appear to be artificial type restrictions in Control.Arrow.ArrowTree. For example, the signature of "deep" is

deep :: (Tree t, ArrowTree a) => a (t b) (t b) -> a (t b) (t b)

instead of the more general

deep :: (Tree t, ArrowTree a) => a (t b) c -> a (t b) c

You are right, there is no harm generalizing deep, since a related combinator, multi, has the more general type. Meanwhile, I don't think

deep (hasName "a") >>> getLink

looks too bad. :) Under suitable assumptions, you can use multi getLink if you want.