Prolog: How to compose two "functions", to find the min of the squares of my list?

Question

I'm learning prolog, and this is the question I have a bit of a problem with right now

Write a Prolog function that takes two parameters: an input list, and an output variable that is the smallest one among the squares of each number in the input list

So far I've been able to make a squaring function

square([], []).  
square([First | Rest], [FirstSquared | SquareRest]) :-
    FirstSquared is First * First,
    square(Rest, SquareRest).

But I don't know how to call this new list as a parameter that would look something like this when pseudo-called in SWI-Prolog

min(square[result_List], Answer).
Answer = *minimum number of list of squares*

Or is there an easier way to implement this in Prolog? If you could please explain the logic behind why you do things a certain way in Prolog, that'd be great since I'm more used to coding in C++ and C#. Thanks!

Answer 1

One of the main paradigms when working in Prolog is state transformation. Your square (perhaps better named squared) predicate transforms a list into a list of squares; what's left is to find the minimum element in that list:

min_square(L, M):-
    squared(L, LS),
    min_list(LS, M).

Writing your own min_list/2 should be straightforward. Just follow the same code skeleton that you used in the squared/2 predicate.

After you've mastered that, the next step in your code development is to fuse the two processing stages into one, as @CapelliC proposes in the comments, by adding one more argument to the squared relation, the minimum-so-far.