PROLOG
%%%
%%% This is one of the example programs from the textbook:
%%%
%%% Artificial Intelligence:
%%% Structures and strategies for complex problem solving
%%%
%%% by George F. Luger and William A. Stubblefield
%%%
%%% Corrections by Christopher E. Davis (chris2d@cs.unm.edu)
%%%
%%% These programs are copyrighted by Benjamin/Cummings Publishers.
%%%
%%% We offer them for use, free of charge, for educational purposes only.
%%%
%%% Disclaimer: These programs are provided with no warranty whatsoever as to
%%% their correctness, reliability, or any other property. We have written
%%% them for specific educational purposes, and have made no effort
%%% to produce commercial quality computer programs. Please do not expect
%%% more of them then we have intended.
%%%
%%% This code has been tested with SWI-Prolog (Multi-threaded, Version 5.2.13)
%%% and appears to function as intended.
%%%%%%%%%%%%%%%%%%%% stack operations %%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% These predicates give a simple, list based implementation of stacks
% empty stack generates/tests an empty stack
member(X,[X|_]).
member(X,[_|T]):-member(X,T).
empty_stack([]).
% member_stack tests if an element is a member of a stack
member_stack(E, S) :- member(E, S).
% stack performs the push, pop and peek operations
% to push an element onto the stack
% ?- stack(a, [b,c,d], S).
% S = [a,b,c,d]
% To pop an element from the stack
% ?- stack(Top, Rest, [a,b,c]).
% Top = a, Rest = [b,c]
% To peek at the top element on the stack
% ?- stack(Top, _, [a,b,c]).
% Top = a
stack(E, S, [E|S]).
%%%%%%%%%%%%%%%%%%%% queue operations %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% These predicates give a simple, list based implementation of
% FIFO queues
% empty queue generates/tests an empty queue
empty_queue([]).
% member_queue tests if an element is a member of a queue
member_queue(E, S) :- member(E, S).
% add_to_queue adds a new element to the back of the queue
add_to_queue(E, [], [E]).
add_to_queue(E, [H|T], [H|Tnew]) :- add_to_queue(E, T, Tnew).
% remove_from_queue removes the next element from the queue
% Note that it can also be used to examine that element
% without removing it
remove_from_queue(E, [E|T], T).
append_queue(First, Second, Concatenation) :-
append(First, Second, Concatenation).
%%%%%%%%%%%%%%%%%%%% set operations %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% These predicates give a simple,
% list based implementation of sets
% empty_set tests/generates an empty set.
empty_set([]).
member_set(E, S) :- member(E, S).
% add_to_set adds a new member to a set, allowing each element
% to appear only once
add_to_set(X, S, S) :- member(X, S), !.
add_to_set(X, S, [X|S]).
remove_from_set(_, [], []).
remove_from_set(E, [E|T], T) :- !.
remove_from_set(E, [H|T], [H|T_new]) :-
remove_from_set(E, T, T_new), !.
union([], S, S).
union([H|T], S, S_new) :-
union(T, S, S2),
add_to_set(H, S2, S_new).
intersection([], _, []).
intersection([H|T], S, [H|S_new]) :-
member_set(H, S),
intersection(T, S, S_new),!.
intersection([_|T], S, S_new) :-
intersection(T, S, S_new),!.
set_diff([], _, []).
set_diff([H|T], S, T_new) :-
member_set(H, S),
set_diff(T, S, T_new),!.
set_diff([H|T], S, [H|T_new]) :-
set_diff(T, S, T_new), !.
subset([], _).
subset([H|T], S) :-
member_set(H, S),
subset(T, S).
equal_set(S1, S2) :-
subset(S1, S2), subset(S2, S1).
%%%%%%%%%%%%%%%%%%%%%%% priority queue operations %%%%%%%%%%%%%%%%%%%
% These predicates provide a simple list based implementation
% of a priority queue.
% They assume a definition of precedes for the objects being handled
empty_sort_queue([]).
member_sort_queue(E, S) :- member(E, S).
insert_sort_queue(State, [], [State]).
insert_sort_queue(State, [H | T], [State, H | T]) :-
precedes(State, H).
insert_sort_queue(State, [H|T], [H | T_new]) :-
insert_sort_queue(State, T, T_new).
remove_sort_queue(First, [First|Rest], Rest).
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