lib/Hcompta/Has.hs

   1 {-# LANGUAGE ConstraintKinds #-}
   2 {-# LANGUAGE FlexibleContexts #-}
   3 {-# LANGUAGE FlexibleInstances #-}
   4 {-# LANGUAGE MultiParamTypeClasses #-}
   5 {-# LANGUAGE TypeFamilies #-}
   6 {-# LANGUAGE TypeOperators #-}
   7 {-# LANGUAGE UndecidableSuperClasses #-}
   8 {-# LANGUAGE UndecidableInstances #-}
   9 module Hcompta.Has where
  10
  11 import Data.Proxy (Proxy(..))
  12 import GHC.Exts (Constraint)
  13
  14 -- * Class 'Has'
  15 type Has ty a = (Get ty a, Set ty a)
  16 -- ** Class 'Get'
  17 class Get ty a where
  18         get :: a -> ty
  19 -- ** Class 'Set'
  20 class Set ty a where
  21         set :: ty -> a -> a
  22
  23 -- * Class 'HasI'
  24 type HasI cl a = (GetI cl a, SetI cl a)
  25 -- ** Type family ':@'
  26 -- | Return the type associated with @cl@ and @a@,
  27 -- and which is an instance of @cl (cl :@ a)@.
  28 type family (:@) (cl:: * -> Constraint) (a:: *) :: *
  29 infixr 9 :@
  30
  31 -- ** Class 'GetI'
  32 class cl (cl:@a) => GetI cl a where
  33         getI :: Proxy cl -> a -> cl:@a
  34 -- ** Class 'SetI'
  35 class cl (cl:@a) => SetI cl a where
  36         setI :: Proxy cl -> cl:@a -> a -> a