{-| Types of nodes and edges of the computational graph.

Parameters:

  * @p@ - is parent node; might be 'OpenKey' or 'NodeKey'

  * @e@ - edge type

  * @a@ - type of the initial node of expression

  * @v@ - type of the node.
-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE GADTs #-}
module Downhill.Internal.Graph.Types
(
  -- * Linear functions
  BackFun(..), FwdFun(..),
  flipBackFun, flipFwdFun
)
 where

import Downhill.Linear.Expr (BasicVector (VecBuilder))


-- | Edge type for backward mode evaluation
newtype BackFun u v = BackFun {unBackFun :: v -> VecBuilder u}

-- | Edge type for forward mode evaluation
newtype FwdFun u v = FwdFun {unFwdFun :: u -> VecBuilder v}

flipBackFun :: BackFun u v -> FwdFun v u
flipBackFun (BackFun f) = FwdFun f

flipFwdFun :: FwdFun u v -> BackFun v u
flipFwdFun (FwdFun f) = BackFun f