chpatrick

{-# LANGUAGE MultiParamTypeClasses, FlexibleInstances, FlexibleContexts, FunctionalDependencies #-}

import Control.Monad.Reader

class Method o m a f | f -> o m a where
  on :: (o -> m a) -> f

instance Method o m a (o -> m a) where
  on = id

chpatrick

{-# LANGUAGE TypeFamilies, KindSignatures, DataKinds, TypeOperators, GADTs, MultiParamTypeClasses, FlexibleInstances, GeneralizedNewtypeDeriving, OverlappingInstances, ScopedTypeVariables, FlexibleContexts #-}

import Control.Applicative
import Control.DeepSeq
import qualified Control.Exception as E

-- Closed type family, needs GHC HEAD.
type family Minus (e :: *) (es :: [*]) :: [*] where
  Minus e '[] = '[]
  Minus e (e ': es) = Minus e es