(*
 *  This file is a component of PropPlan - a model-based planner
 *  Copyright (C) 2000-2007  Michael Paul Fourman
 *  homepages.inf.ed.ac.uk/mfourman/tools/propplan
 *  sourceforge.net/projects/propplan
 *  michael.fourman (AT) gmail.com
 *
 *  This program is free software: you can redistribute it and/or modify
 *  it under the terms of version 3 of the GNU Affero General Public License
 *  as published by the Free Software Foundation.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received the file COPYING, a copy of the GNU Affero 
 *  Public License, along with this program.  
 *  If not, see <http://www.gnu.org/licenses/>.
 
 *  $Id: DICTIONARY.ML,v 1.1 2007/12/30 15:31:25 michaelfourman Exp $
 *)

signature DICTIONARY =
sig
   type Key
   type 'a Dict
   exception Lookup
   val empty  :  'a Dict
   val lookup :  'a Dict -> Key -> 'a
   val remove : Key *  'a Dict ->  'a Dict
   val enter  : (Key * 'a) *  'a Dict -> 'a Dict
end

functor DICTIONARY( eqtype Key ):DICTIONARY =
struct
    type Key  = Key
    exception Lookup
    datatype 'a Dict = D of (Key * 'a) list
        val empty = D []
        
        fun lookup (D((k,e)::t)) key = if(k = key)then e
                                        else lookup (D t) key
          | lookup _ _ = raise Lookup

        fun rem _ [] = []
          | rem key ((entry as (k,_))::t) = if(k = key) then rem key t (* this should be redundant *)
                                       else entry :: rem key t

        fun ent ((k,e),  []) = [(k, e)]
          | ent ((k,e), ((k',e') :: entries)) = 
		if k = k' then raise Lookup
		else
			(k',e') :: ent ((k,e), entries) 
        fun enter (ke, D entries) = D (ent(ke, entries) ) 
        fun remove (key, D entries) = D(rem key entries)

        fun alist (D l) = l

	fun size (D []) = 0 | size (D (_ :: t)) = 1 + size (D t);
end;