oct 31 prolog tutorial

Frederik/README.md

@@ -4,4 +4,5 @@ Readme
 AI 1 - 2019/2020
 ---
 
-* 2019-10-28: `2019-10-28-tutorial.pl` (simple prolog exercises)
+* 2019-10-28: `prolog/2019-10-28-tutorial.pl` (simple prolog exercises)
+* 2019-10-31: `prolog/2019-10-31-tutorial.pl` (simple prolog exercises)

Frederik/prolog/2019-10-31-tutorial.pl

+% INTRODUCTION
+
+animal(elephant).
+
+bigger(elephant, bird).
+bigger(elephant, cow).
+bigger(cow, mouse).
+
+bigger(X, Y) :-
+    bigger(X, A), bigger(A, Y).
+
+% Note: The above definition for a transitive relation
+% results in loop, which wasn't resolved during the tutorial.
+% If you want to know more about it, take a look at this answer:
+% https://stackoverflow.com/a/28615704
+
+
+% SIMPLE LIST TASKS
+% inspired from http://www.ic.unicamp.br/~meidanis/courses/mc336/2009s2/prolog/problemas/
+
+getfirst([X|_], X).
+
+getlast([X], X).
+getlast([_|R], X) :-
+    getlast(R, X).
+
+getsecondlast([X,_], X).
+getsecondlast([_|R], X) :-
+    getsecondlast(R, X).
+
+getlength([], 0).
+getlength([X|R], L) :-
+    getlength(R, N), L is N+1.
+
+second([], []).
+second([X], [X]).
+second([X,Y|R], [X|S]) :-
+    second(R, S).
+
+fourth(X, Y) :-
+    second(X, Z), second(Z, Y).
+
+prepend(X,SomeList,[X|SomeList]).
+
+duplicate([], []).
+duplicate([X|R], [X,X|S]) :-
+    duplicate(R, S).
+
+
+% INSERTION SORT
+
+insert(X, [], [X]).
+insert(X, [H|R], [H|S]) :-
+    X >= H, insert(X, R, S).
+insert(X, [H|R], [X,H|R]) :-
+    X =< H.
+
+inssort([], []).
+inssort([H|T], L) :-
+    inssort(T, TSorted),
+    write('inserting '),
+    write(H),
+    write('\n'),
+    insert(H, TSorted, L).
+