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Prolog Source  |  1988-06-21  |  643 b   |  28 lines
  1. /*
  2.    Turbo Prolog 2.0 Chapter 18, Example Program 2
  3.    
  4.    Copyright (c) 1986, 88 by Borland International, Inc
  5.    
  6. */
  7.    
  8. domains
  9.    town     = symbol
  10.    distance = integer
  11.  
  12. predicates
  13.    road(town, town, distance)
  14.    route(town, town, distance)
  15.  
  16. clauses
  17.    road(tampa, houston, 200).
  18.    road(gordon, tampa, 300).
  19.    road(houston, gordon, 100).
  20.    road(houston, kansas_city, 120).
  21.    road(gordon, kansas_city, 130).
  22.    route(Town1, Town2, Distance) :-
  23.       road(Town1, Town2, Distance).
  24.    route(Town1, Town2, Distance) :-
  25.       road(Town1, X, Dist1),
  26.       route(X, Town2, Dist2),
  27.       Distance=Dist1+Dist2, !.
  28.