Trivial.hs

-- |
-- Module      :  Data.Constraint.Trivial
-- Copyright   :  (c) 2014-2016 Justus Sagemüller
-- License     :  GPL v3 (see LICENSE)
-- Maintainer  :  (@) jsagemue $ uni-koeln.de
-- 
{-# LANGUAGE FlexibleInstances     #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE ConstraintKinds       #-}

module Data.Constraint.Trivial (
            Unconstrained, Impossible
          , Unconstrained2, Impossible2
          , Unconstrained3, Impossible3
          , Unconstrained4, Impossible4
          , Unconstrained5, Impossible5
          , Unconstrained6, Impossible6
          , Unconstrained7, Impossible7
          , Unconstrained8, Impossible8
          , Unconstrained9, Impossible9
          ) where

-- | Intended to be used as an argument for some type constructor which expects kind
--   @* -> Constraint@, when you do not actually wish to constrain anything with it.
--   
--   @'Unconstrained' t@ can always be added to the constraint list of any signature, without
--   changing anything.
class Unconstrained t
instance Unconstrained t


-- | This constraint can /never/ be fulfilled. Might be useful e.g. as a default
--   for a class-associated constraint; this basically disables any method with
--   that constraint (so it can safely be left 'undefined').
type Impossible t = HiddenEmptyClass t

class HiddenEmptyClass t


-- | Like 'Unconstrained', but with kind signature @* -> * -> Constraint@
--   (two unconstrained types).
class Unconstrained2 t s
instance Unconstrained2 t s

type Impossible2 t s = HiddenEmptyClass2 t s
class HiddenEmptyClass2 t s


class Unconstrained3 t s r
instance Unconstrained3 t s r

type Impossible3 t s r = HiddenEmptyClass3 t s r
class HiddenEmptyClass3 t s r


class Unconstrained4 t s r q
instance Unconstrained4 t s r q

type Impossible4 t s r q = HiddenEmptyClass4 t s r q
class HiddenEmptyClass4 t s r q


class Unconstrained5 t s r q p
instance Unconstrained5 t s r q p

type Impossible5 t s r q p = HiddenEmptyClass5 t s r q p
class HiddenEmptyClass5 t s r q p


class Unconstrained6 t s r q p o
instance Unconstrained6 t s r q p o

type Impossible6 t s r q p o = HiddenEmptyClass6 t s r q p o
class HiddenEmptyClass6 t s r q p o


class Unconstrained7 t s r q p o n
instance Unconstrained7 t s r q p o n

type Impossible7 t s r q p o n = HiddenEmptyClass7 t s r q p o n
class HiddenEmptyClass7 t s r q p o n


class Unconstrained8 t s r q p o n m
instance Unconstrained8 t s r q p o n m

type Impossible8 t s r q p o n m = HiddenEmptyClass8 t s r q p o n m
class HiddenEmptyClass8 t s r q p o n m


class Unconstrained9 t s r q p o n m l
instance Unconstrained9 t s r q p o n m l

type Impossible9 t s r q p o n m l = HiddenEmptyClass9 t s r q p o n m l
class HiddenEmptyClass9 t s r q p o n m l