{-# LANGUAGE ConstraintKinds #-} -- For type class synonyms
{-# LANGUAGE PolyKinds #-}
{-# LANGUAGE DefaultSignatures #-} -- For adding LiftDerived* constraints
module Symantic.Derive where

import Data.Function ((.))
import Data.Kind (Type)

-- * Type family 'Derived'
-- | The next 'Semantic' that @(sem)@ derives to.
type family Derived (sem :: Semantic) :: Semantic

-- * Class 'Derivable'
-- | Derive an interpreter to another interpreter
-- determined by the 'Derived' open type family.
-- This is mostly useful when running the interpreter stack,
-- but also when going back from an initial encoding to a final one.
--
-- Note that 'derive' and 'liftDerived' are not necessarily reciprocical functions.
class Derivable sem where
  derive :: sem a -> Derived sem a

-- * Class 'LiftDerived'
-- | Lift the 'Derived' interpreter of an interpreter, to that interpreter.
-- This is mostly useful to give default values to class methods
-- in order to skip their definition for interpreters
-- where 'liftDerived' can already apply the right semantic.
--
-- Note that 'derive' and 'liftDerived' are not necessarily reciprocical functions.
class LiftDerived sem where
  liftDerived :: Derived sem a -> sem a

-- * Class 'LiftDerived1'
-- | Convenient wrapper of 'derive' and 'liftDerived' for functions with a single argument.
class LiftDerived1 sem where
  liftDerived1 ::
    (Derived sem a -> Derived sem b) ->
    sem a -> sem b
  liftDerived1 f = liftDerived . f . derive
  default liftDerived1 ::
    LiftDerived sem => Derivable sem =>
    (Derived sem a -> Derived sem b) ->
    sem a -> sem b

-- * Class 'LiftDerived2'
-- | Convenient wrapper of 'derive' and 'liftDerived' for functions with two arguments.
-- Note that the default instance relies upon 'LiftDerived', not 'LiftDerived1'.
class LiftDerived2 sem where
  liftDerived2 ::
    (Derived sem a -> Derived sem b -> Derived sem c) ->
    sem a -> sem b -> sem c
  liftDerived2 f a b = liftDerived (f (derive a) (derive b))
  default liftDerived2 ::
    LiftDerived sem => Derivable sem =>
    (Derived sem a -> Derived sem b -> Derived sem c) ->
    sem a -> sem b -> sem c

-- * Class 'LiftDerived3'
-- | Convenient wrapper of 'derive' and 'liftDerived' for functions with three arguments.
-- Note that the default instance relies upon 'LiftDerived', not 'LiftDerived2'.
class LiftDerived3 sem where
  liftDerived3 ::
    (Derived sem a -> Derived sem b -> Derived sem c -> Derived sem d) ->
    sem a -> sem b -> sem c -> sem d
  liftDerived3 f a b c = liftDerived (f (derive a) (derive b) (derive c))
  default liftDerived3 ::
    LiftDerived sem => Derivable sem =>
    (Derived sem a -> Derived sem b -> Derived sem c -> Derived sem d) ->
    sem a -> sem b -> sem c -> sem d

-- * Class 'LiftDerived4'
-- | Convenient wrapper of 'derive' and 'liftDerived' for functions with three arguments.
-- Note that the default instance relies upon 'LiftDerived', not 'LiftDerived3'.
class LiftDerived4 sem where
  liftDerived4 ::
    (Derived sem a -> Derived sem b -> Derived sem c -> Derived sem d -> Derived sem e) ->
    sem a -> sem b -> sem c -> sem d -> sem e
  liftDerived4 f a b c d = liftDerived (f (derive a) (derive b) (derive c) (derive d))
  default liftDerived4 ::
    LiftDerived sem => Derivable sem =>
    (Derived sem a -> Derived sem b -> Derived sem c -> Derived sem d -> Derived sem e) ->
    sem a -> sem b -> sem c -> sem d -> sem e

-- * Type synonyms @FromDerived*@
-- | Convenient type synonym for using 'liftDerived' on 'Syntax' @(syn)@.
type FromDerived  syn sem = ( LiftDerived  sem, syn (Derived sem) )
type FromDerived1 syn sem = ( LiftDerived1 sem, syn (Derived sem) )
type FromDerived2 syn sem = ( LiftDerived2 sem, syn (Derived sem) )
type FromDerived3 syn sem = ( LiftDerived3 sem, syn (Derived sem) )
type FromDerived4 syn sem = ( LiftDerived4 sem, syn (Derived sem) )