Full pipes compatibility

[tomjaguarpaw]

This is a very cool library! I like how general it is.

The definition of Proxy from pipes is

data Proxy a' a b' b m r
    = Request a' (a  -> Proxy a' a b' b m r )
    | Respond b  (b' -> Proxy a' a b' b m r )
    | M          (m    (Proxy a' a b' b m r))
    | Pure    r

It seems like you can replicate this in streaming by Stream (Proxy a' a b' b) m r where

data Proxy a' a b' b z
    = Request a' (a  -> z)
    | Respond b  (b' -> z)

(a different Proxy, of course). Any interest in adding something like this? I'm not going to use it now but I thought it was worth recording .