It’s useful, but in my opinion not yet ideal because I cannot cut duplicate paths at the point of their creation. Consider, with the complete graph K_n: n_complete(N, Es) :- numlist(1, N, Ns), phrase(pairs(Ns), Es). adjacent(Edges, X, Y) :- member(edge(X, Y), Edges). pairs([]) –> []. pairs([N|Ns]) –> edges(Ns, N), pairs(Ns). edges([], _) –> []. edges([N|Ns], … Read more
How about defining path/4 like this? path(R_2, Xs, A,Z) :- % A path `Xs` from `A` to `Z` is … walk(R_2, Xs, A,Z), % … a walk `Xs` from `A` to `Z` … all_dif(Xs). % … with no duplicates in `Xs`. To aid universal termination, we swap the two goals in above conjunction … path(R_2, … Read more
Single quoted items are always atoms. The meaning of double quotes depends on the Prolog flag double_quotes: atom — with this value “a” = a. Nowadays, this is rarely used. But you will find Prolog books where [“abc.pl”] is written. codes — a list of character codes. This is frequently the default, but it leads … Read more
This is usually called maplist/3 and is part of the Prolog prologue. Note the different argument order! :- meta_predicate(maplist(2, ?, ?)). maplist(_C_2, [], []). maplist( C_2, [X|Xs], [Y|Ys]) :- call(C_2, X, Y), maplist( C_2, Xs, Ys). The different argument order permits you to easily nest several maplist-goals. ?- maplist(maplist(test),[[1,2],[3,4]],Rss). Rss = [[1,4],[9,16]]. maplist comes in … Read more
union(A, B, C, U) :- union(A, B, V), union(C, V, U). Your definition of union/3 can be improved by replacing … not(element(X,L)), … by … maplist(dif(X),L), … or … non_member(X, L), …. non_member(_X, []). non_member(X, [E|Es]) :- dif(X, E), non_member(X, Es). Here is a case where the difference shows: ?- union([A],[B],[C,D]). A = C, B … Read more
When describing a list, always consider using DCGs. In your case, you can very easily obtain what you want with a few simple modifications to your code: show_result(Squares,MaxRow,MaxCol, List) :- phrase(show_result(Squares,MaxRow,MaxCol,1), List). show_result(_,MaxRow,_,Row) –> { Row > MaxRow }, !. show_result(Squares,MaxRow,MaxCol,Row) –> { phrase(show_result(Squares,MaxRow,MaxCol,Row,1), Line) } , [Line], { Row1 is Row+1 }, show_result(Squares,MaxRow,MaxCol,Row1). show_result(_,_,MaxCol,_,Col) … Read more