span

練習。

% span.pro

:- module(span, [span/2]).

span(From, From, [From]) :- !.
span(From, To, [From|Span]) :-
  From < To,
  From1 is From + 1,
  span(From1, To, Span),
  !.

% span-test.pro

:- include(span).

main :-
  span(1, 10, S),
  format("~p~n", [S]),
  halt.

実行。

$ gprolog --consult-file span-test.pro --entry-goal main
[1,2,3,4,5,6,7,8,9,10]

通常使うには between で充分なのだけれど。

$ gprolog
| ?- findall(N, between(1, 10, N), NS).
NS = [1,2,3,4,5,6,7,8,9,10]
yes