-- | Offers an 'activePair' pattern for convenient implementation of interaction nets.
module GraphRewriting.Pattern.InteractionNet where

import Prelude.Unicode
import Data.View
import GraphRewriting.Graph.Types
import GraphRewriting.Graph.Read
import GraphRewriting.Pattern


-- | Index that identifies the principal port within the list of ports
class INet v where principalPort ∷ v → Int

-- | Instead of @(,)@ to save parentheses
data Pair x = x :-: x

pair ∷ Pair a → (a,a)
pair (x :-: y) = (x,y)

activePair ∷ (View [Port] n, View v n, INet v) ⇒ Pattern n (Pair v)
activePair = do
	v1 ← node
	n1 ← previous
	ports1 ← liftReader (inspectNode n1)
	let pp1 = ports1 !! principalPort v1
	v2 ← adverse pp1 n1
	n2 ← previous
	ports2 ← liftReader (inspectNode n2)
	let pp2 = ports2 !! principalPort v2
	require (pp1 ≡ pp2)
	return (v1 :-: v2)