lib/Hcompta/Has.hs

   1 {-# LANGUAGE AllowAmbiguousTypes #-}
   2 {-# LANGUAGE ConstraintKinds #-}
   3 {-# LANGUAGE UndecidableInstances #-}
   4 {-# LANGUAGE UndecidableSuperClasses #-}
   5 module Hcompta.Has where
   6
   7 import Data.Proxy (Proxy(..))
   8 import GHC.Exts (Constraint)
   9
  10 -- * Class 'Has'
  11 type Has ty a = (Get ty a, Set ty a)
  12
  13 -- ** Class 'Get'
  14 class Get ty a where
  15         get :: a -> ty
  16
  17 -- ** Class 'Set'
  18 class Set ty a where
  19         set :: ty -> a -> a
  20
  21 -- * Class 'HasI'
  22 type HasI cl a = (GetI cl a, SetI cl a)
  23
  24 -- ** Type family ':@'
  25 -- | Return the type associated with @cl@ and @a@,
  26 -- and which is an instance of @cl (cl :@ a)@.
  27 type family (:@) (cl:: * -> Constraint) (a:: *) :: *
  28 infixr 9 :@
  29
  30 -- ** Class 'GetI'
  31 class cl (cl:@a) => GetI cl a where
  32         getI_ :: Proxy cl -> a -> cl:@a
  33
  34 -- | Convenient helper to be used with 'TypeApplications'.
  35 getI :: forall cl a. GetI cl a => a -> cl:@a
  36 getI = getI_ (Proxy::Proxy cl)
  37
  38 -- ** Class 'SetI'
  39 class cl (cl:@a) => SetI cl a where
  40         setI_ :: Proxy cl -> cl:@a -> a -> a
  41
  42 -- | Convenient helper to be used with 'TypeApplications'.
  43 setI :: forall cl a. SetI cl a => cl:@a -> a -> a
  44 setI = setI_ (Proxy::Proxy cl)