Advent of Code 2022 #1 in Prolog (Trealla Prolog)

aoc2022-1.pl

% caveat: add an extra line break to the input :-)

:- use_module(library(dcgs)).
:- use_module(library(pio)).

elves([N|Ns]) --> elf(N), elves(Ns).
elves([]) --> [].
elf(Calories) --> sum(Calories), nl.

sum(X) --> number(A), nl, sum(B), { X is A + B }.
sum(0) --> [].

nl --> ['\n'].

% is there a better way to do this? copy-pasted it from another project
number(N) --> { number(N), number_chars(N, D) }, digits(D).
number(N) --> { var(N) }, digits(D), { number_chars(N, D) }.
digits([D|Ds]) 	 --> digit(D), digits_r(Ds).
digits_r([D|Ds]) --> digits([D|Ds]).
digits_r([]) 	 --> [].
digit(D) --> [D], { char_type(D, digit) }.

main :-
	once(phrase_from_file(elves(Elves), 'input.txt')),
	sort(Elves, Sorted),
	reverse(Sorted, [Top1, Top2, Top3|_]),
	Sum is Top1 + Top2 + Top3,
	format("Top 3: ~w~n", [Sum]).