Knowing when to use cut in prolog

TL;DR: Don’t. The cut prunes Prolog’s search tree. That is, given a pure Prolog program without cut and the same program with cuts the only difference is that the program with cuts might spend less time in fruitless branches, and thus is more efficient ; might have fewer answers ; it might also terminate whereas … Read more

Using \==/2 or dif/2

For elegance and didactic reasons alone, dif/2 is clearly preferable here and also in the vast majority of other cases, since as you already note “a lot of unnecessary unifications might take place” otherwise, and also because dif/2 is a pure and nicely declarative predicate that can be used in all directions and at any … Read more

reversible “binary to number” predicate

Use CLP(FD) constraints, for example: :- use_module(library(clpfd)). binary_number(Bs0, N) :- reverse(Bs0, Bs), foldl(binary_number_, Bs, 0-0, _-N). binary_number_(B, I0-N0, I-N) :- B in 0..1, N #= N0 + B*2^I0, I #= I0 + 1. Example queries: ?- binary_number([1,0,1], N). N = 5. ?- binary_number(Bs, 5). Bs = [1, 0, 1] . ?- binary_number(Bs, N). Bs = … Read more

Shuffle in prolog

shuffle([], B, B). shuffle([H|A], B, [H|S]) :- shuffle(B, A, S). In this kind of problems, usually the difficult part is not Prolog but identifying the simplest recursive relation that solves it.

Explanation of a Prolog algorithm to append two lists together

First, let’s translate the clauses into something more understandable: append([], List, List) :- !. can be written append([], List2, Result) :- Result = List2, !. and append([H|L1], List2, [H|L3]) :- append(L1, List2, L3). can be written append(List1, List2, Result) :- List1 = [Head1 | Tail1], Result = [HeadR | TailR], Head1 = HeadR, append(Tail1, List2, … Read more