Proxy.hs

{-# LANGUAGE ConstraintKinds #-}
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE KindSignatures #-}
{-# LANGUAGE PolyKinds #-}

module Ivory.Language.Proxy
  (
  -- * Proxy
    Proxy(..)
  , SProxy
  -- * Nat
  , ANat
  , NatType
  , aNat
  , fromTypeNat
  -- * Symbol
  , ASymbol
  , SymbolType
  , aSymbol
  , fromTypeSym
  ) where

import Data.Proxy   (Proxy (..))
import GHC.TypeLits (KnownNat, KnownSymbol, Nat, Symbol, natVal, symbolVal)

-- | Type proxies for * types.
type SProxy a = Proxy (a :: *)

type ANat    n = KnownNat n
type NatType n = Proxy n
aNat :: KnownNat n => Proxy n
aNat = Proxy

type ASymbol    s = (KnownSymbol s)
type SymbolType s = Proxy s
aSymbol :: KnownSymbol s => Proxy s
aSymbol = Proxy

-- | The string associated with a type-symbol.
fromTypeSym :: KnownSymbol sym => proxy (sym :: Symbol) -> String
fromTypeSym  = symbolVal

-- | The integer associated with a type-nat.
fromTypeNat :: KnownNat i => proxy (i :: Nat) -> Integer
fromTypeNat  = natVal