{-# LANGUAGE
  EmptyDataDecls,
  FlexibleContexts,
  FlexibleInstances,
  MultiParamTypeClasses,
  TypeFamilies
  #-}
module Data.HList.Graph
    ( Graph(..)
    , NodeSet
    , NodeIDSet
    , Node(..)
    , LPath(..)

    , IsEmpty

    , NodeIDA
    )
    where

import Data.HList.Prelude

-- NodeSet
class    NodeSet ns
instance NodeSet Nil
instance NodeSet ns => NodeSet (Cons n ns)

-- NodeIDSet
class    NoDuplicates ids => NodeIDSet ids
instance NodeIDSet Nil
instance (OccursNot id ids, NodeIDSet ids) => NodeIDSet (Cons id ids)

-- LPath (list of labeled node IDs)
class    LPath p
instance LPath Nil
instance LPath p => LPath (Cons (Cons l id) p)

-- Node
class NodeIDSet (LinksFrom n) => Node n
    where
      type NodeID n
      type LinksFrom n

-- NodeIDA
data NodeIDA
instance ApplyT NodeIDA n where
    type Apply NodeIDA n = NodeID n

-- Graph
class ( NodeSet (Nodes g)
      , NoDuplicates (Map NodeIDA g)
      )
    => Graph g
    where
      type Empty g
      type Nodes g

-- IsEmpty
type family IsEmpty g