writelist([]).
writelist([ Head | Tail ]) :-
    write(' - '), write(Head), nl,
    writelist(Tail).

concat([], List, List). % Stopping condition - The 2nd list and the result are one and the same
% Add the head of the first lsit onto the result
concat([ Head | Tail ], List2, [ Head | Result ]) :-
    concat(Tail, List2, Result). % Recursively add the next item in the first list to the result

countlist([ LastItem | [] ], LastItem).
countlist([ Head | Rest ], Result) :-
    countlist(Rest, RecursiveResult),
    Result is RecursiveResult + Head.

listlength([ _ | [] ], 1).
listlength([ _ | Tail ], Result) :-
    listlength(Tail, RecursiveResult),
    Result is RecursiveResult + 1.

loves(cat, milk).
loves(dog, bone).
loves(mouse, cheese).
loves(cat, cheese).

% ?- findall(Who, loves(Who, cheese), Result), writelist(Result).

score(ben, 45).
score(john, 30).
score(bob, 25).
score(jim, 34).

averageScore(Average) :-
    findall(What, score(_, What), ScoreList),
    countlist(ScoreList, Count),
    listlength(ScoreList, Length),
    Average is Count / Length.

isa(polly, parrot).
isa(parrot, bird).
isa(bird, living_thing).
hasa(parrot, wings(2)).
hasa(polly, perch).
hasa(polly, colour(green)).

% ?- findall(green_birds(Who), hasa(Who, colour(green)), Result).