# Copyright (C) 2007-2008, Jeff Thompson
# 
# All rights reserved.
# 
# Redistribution and use in source and binary forms, with or without 
# modification, are permitted provided that the following conditions are met:
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#     * Redistributions of source code must retain the above copyright 
#       notice, this list of conditions and the following disclaimer.
#     * Redistributions in binary form must reproduce the above copyright 
#       notice, this list of conditions and the following disclaimer in the 
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#     * Neither the name of the copyright holder nor the names of its contributors 
#       may be used to endorse or promote products derived from this software 
#       without specific prior written permission.
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# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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# PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
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import sys
# Hack sys.path for the examples.
sys.path.append("../..")
from YP import *
from Variable import *
from Atom import *
from ListPair import *

def main():
    print "Return a list of 2 elements:"
    List = Variable()
    for l1 in makeList("a", "b", List):
        print "List =", List.getValue()

    print "Unify two lists:"
    Second = Variable()
    for l1 in makeList("x", Second,
          ListPair("x", ListPair("y", Atom.NIL))):
        print "The second element is", Second.getValue()

def makeList(First, Second, List):
    list1 = ListPair(Second, Atom.NIL)
    result = ListPair(First, list1)
    for l1 in YP.unify(List, result):
        yield False

main()


