QuantifiedVar.hs

{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE UndecidableInstances #-}

-- | A class for types that have quantified variables.
module Hyper.Unify.QuantifiedVar
    ( HasQuantifiedVar (..)
    , MonadQuantify (..)
    , OrdQVar
    ) where

import Control.Lens (Prism')
import Hyper.Type (HyperType)

import Prelude.Compat

-- | Class for types which have quantified variables
class HasQuantifiedVar (t :: HyperType) where
    -- | The type of quantified variable identifiers
    type QVar t

    -- | A `Prism'` from a type to its quantified variable term
    quantifiedVar :: Prism' (t f) (QVar t)

-- | A constraint synonym that represents that
-- the quantified variable of a type has an 'Ord' instance
class (HasQuantifiedVar t, Ord (QVar t)) => OrdQVar t

instance (HasQuantifiedVar t, Ord (QVar t)) => OrdQVar t

-- | A monad where new quantified variables can be generated
class MonadQuantify typeConstraints q m where
    newQuantifiedVariable :: typeConstraints -> m q