;;; lib/obj/graph.lisp --- Graphs

 ;;

 ;;; Code:

 (in-package :obj/graph)

 ;;; Vertex

 (defclass vertex (node id)

   ()

   (:documentation "generic vertex mixin. The difference between this class and NODE is

 that a vertex always carries an ID slot."))

 ;;; Edge

 (defclass edge (node id)

   ()

   (:documentation "generic edge mixin. Compatible with the NODE and ID protocols."))

 (defclass directed-edge (edge))

 (defclass undirected-edge (edge))

 (defclass weighted-edge (edge)

   ((weight :initform 1d0 :initarg :weight :accessor weight-of)))

 (defgeneric edge-weight (edge &key &allow-other-keys)

   (:method ((edge t) &key &allow-other-keys) (values 1.0)))

 ;;; Graph

 (defclass graph ()

   ()

   (:documentation "generic graph mixin."))