So one chapter of the 7 languages in 7 weeks book was Prolog. Yeah, it’s an older language but it s really fun. Since i ve been doing imperative style programming for so long it was quite literally mind-bending. It kept me up late playing like I used to with Java way back in the late 90s, in other words it was freakin fun. At any rate, I won t regurgitate any summaries of Prolog (there are plenty), but i will leave some code examples.

The example listed below was a totally simple program designed to return the smallest integer from a list (totally basic I know), but what i m also including here is the unit test and command line version too just for the hell of it.

file d2_2.pl

smallest([L,R],S) :- L<R -> S=L;S=R,!.
smallest([H|T], S) :- smallest(T,ST), smallest([H,ST], S),!.
smallest([S],S).

file test_d2_2.pl

assert(Source,Expected,Expected) :-
write('\nOK - For '), write(Source),
'url':'http://trevershick.github.io' write(' expected '),write(Expected), write('
and'),
write(' received '),write(Expected), !.

assert(Source,Expected,Received) :-
write('\nFAIL - For '), write(Source),
write(' expected '),write(Expected), write(' but'),
write(' received '),write(Received), !.

assert_smallest(List,Expected) :-
smallest(List,Received), assert(List,Expected,Received).

test_smallest :-
write('Begin Tests------------------------------------------------'),
assert_smallest([3,1,2],1),
assert_smallest([-66,32,123,1223,10003,1,2],-66),
assert_smallest([0],0),
assert_smallest([-1,0],-1),
write('\n-----------------------------------------------------------\n').

:- include(d2_2).
:- initialization(test_smallest).

file cmd_d2_2.pl

iargs(R) :-
        argument_list(S),
        iargs(S,R).

iargs([],[]).
iargs([H|T],R) :-
        iargs(T,TR),
        number_atom(HASINT,H),
        append([HASINT],TR,R).



q :-
        iargs(S),
        smallest(S,SM),
        write('Smallest of '),
        write(S),
        write(' is '),
        write(SM),
        write('\n').

:- include(d2_2).
:- initialization(q).

So, yeah, i know that’s totally simple but for people just starting out it might prove useful.

I think for Prolog to be a tool that I would choose I d have to be using it for months first. It s kind of the chicken and the egg problem unfortunately. If i had a lot of spare time between work/child/running I would work on building stuff with Prolog but i m not sure that will happen. If i do write something however I will post it.

Oh, BTW, this wasn’t the only Prolog thing we did. We did the standard fibonacci and factorial problems as well as the standard map coloring problem (couldn t write that myself - need more practice.) but i won t include the code here.