[tutor] Update assignment

examples/lists/merlin.pl

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+% Merlin's Potion lab
+
+:- dynamic ingredient/1.
+
+% Rules of the game
+
+% Add a new ingredient if it's not already present
+add_ingredient(Item) :-
+    \+ ingredient(Item),
+    assertz(ingredient(Item)),
+    write('Added ingredient: '), write(Item), nl.
+
+% Use an ingredient (remove it from memory)
+use_ingredient(Item) :-
+    ingredient(Item),
+    retract(ingredient(Item)),
+    write('Used ingredient: '), write(Item), nl.
+
+% Make a potion from two ingredients
+make_potion(Item1, Item2) :-
+    ingredient(Item1),
+    ingredient(Item2),
+    Item1 \= Item2,
+    retract(ingredient(Item1)),
+    retract(ingredient(Item2)),
+    write('You mixed '), write(Item1), write(' and '), write(Item2),
+    write(' to create a potion!'), nl.
+
+% Show what's left
+show_ingredients :-
+    findall(X, ingredient(X), List),
+    write('Remaining ingredients: '), write(List), nl.
+
+% Reset lab
+reset_lab :-
+    retractall(ingredient(_)),
+    write('Potion lab reset.'), nl.
+
+% Merlin's recipes
+
+stock :-
+    add_ingredient(wolfsbane),
+    add_ingredient(mandrake),
+    add_ingredient(unicorn_blood),
+    add_ingredient(phoenix_feather),
+    add_ingredient(dittany).
+
+brew :-
+    stock,
+    make_potion(wolfsbane, mandrake),
+    show_ingredients.
+
+:- initialization(brew).

examples/lists/zebra.pl

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+%%  houses(-Solution)
+%   @param  Solution is a list of houses that satisfy all constraints.
+%   @author Folklore attributes this puzzle to Einstein
+%   @see http://en.wikipedia.org/wiki/Zebra_Puzzle
+
+/* Houses logical puzzle: who owns the zebra and who drinks water?
+
+	 1) Five colored houses in a row, each with an owner, a pet, cigarettes, and a drink.
+	 2) The English lives in the red house.
+	 3) The Spanish has a dog.
+	 4) They drink coffee in the green house.
+	 5) The Ukrainian drinks tea.
+	 6) The green house is next to the white house.
+	 7) The Winston smoker has a serpent.
+	 8) In the yellow house they smoke Kool.
+	 9) In the middle house they drink milk.
+	10) The Norwegian lives in the first house from the left.
+	11) The Chesterfield smoker lives near the man with the fox.
+	12) In the house near the house with the horse they smoke Kool.
+	13) The Lucky Strike smoker drinks juice.
+	14) The Japanese smokes Kent.
+	15) The Norwegian lives near the blue house.
+
+Who owns the zebra and who drinks water?
+*/
+
+zebra_owner(Owner) :-
+	houses(Hs),
+	member(h(Owner,zebra,_,_,_), Hs).
+
+water_drinker(Drinker) :-
+	houses(Hs),
+	member(h(Drinker,_,_,water,_), Hs).
+
+houses(Hs) :-
+	% each house in the list Hs of houses is represented as:
+	%      h(Nationality, Pet, Cigarette, Drink, Color)
+	length(Hs, 5),                                            %  1
+	member(h(english,_,_,_,red), Hs),                         %  2
+	member(h(spanish,dog,_,_,_), Hs),                         %  3
+	member(h(_,_,_,coffee,green), Hs),                        %  4
+	member(h(ukrainian,_,_,tea,_), Hs),                       %  5
+	next(h(_,_,_,_,green), h(_,_,_,_,white), Hs),             %  6
+	member(h(_,snake,winston,_,_), Hs),                       %  7
+	member(h(_,_,kool,_,yellow), Hs),                         %  8
+	Hs = [_,_,h(_,_,_,milk,_),_,_],                           %  9
+	Hs = [h(norwegian,_,_,_,_)|_],                            % 10
+	next(h(_,fox,_,_,_), h(_,_,chesterfield,_,_), Hs),        % 11
+	next(h(_,_,kool,_,_), h(_,horse,_,_,_), Hs),              % 12
+	member(h(_,_,lucky,juice,_), Hs),                         % 13
+	member(h(japanese,_,kent,_,_), Hs),                       % 14
+	next(h(norwegian,_,_,_,_), h(_,_,_,_,blue), Hs),          % 15
+	member(h(_,_,_,water,_), Hs),		% one of them drinks water
+	member(h(_,zebra,_,_,_), Hs).		% one of them owns a zebra
+
+next(A, B, Ls) :- append(_, [A,B|_], Ls).
+next(A, B, Ls) :- append(_, [B,A|_], Ls).
+
+/** <examples>
+
+?- zebra_owner(Owner).
+
+?- water_drinker(Drinker).
+
+?- houses(Houses).
+
+*/
+
+main :- findall(Houses, houses(Houses), Results), write(Results), nl.
+
+:- initialization(main).
+
+/* source: SWISH https://swish.swi-prolog.org/example/houses_puzzle.pl */
+