Note that nobody was suggesting two pragmas with incompatible behaviors, only to have just one symbol reserved to still be able to have type operator variables.

I do like your suggestion, although >--c--> is quite a bit longer than ~>.

Sjoerd

On Sep 17, 2012, at 6:28 PM, Iavor Diatchki wrote:

Hello,

I think that it would be a mistake to have two pragmas with incompatible behaviors: for example, we would not be able to write modules that use Conal's libraries and, say, the type nats I've been working on.

If the main issue is the notation for arrows, has anoyone played with what can be done with the current (7.6) system? I just thought of two variations that seem to provide a decent notation for writing arrow-ish programs. The second one, in particular, mirrors the arrow notation at the value level, so perhaps that would be enough?

-Iavor

{-# LANGUAGE TypeOperators, KindSignatures #-}
module Test where

import Control.Category

-- Variant 1: Post-fix annotation

type (a ---> b) c = c a b

f :: Category c => (x ---> y) c -> (y ---> z) c -> (x ---> z) c
f = undefined

-- Variant 2: Arrow notation

type a >-- (c :: * -> * -> *) = c a
type c --> b = c b

infix 2 >--

infix 1 -->

g :: Category c => (x >--c--> y) -> (y >--c--> z) -> (x >--c--> z)

g = undefined

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