elxlog

% 8-queens program
test() :- queen([1,2,3,4,5,6,7,8],X),write(X),nl(),fail().

queen(Data, Out) :-
	queen_2(Data, [], Out).

queen_2([], _, []).
queen_2([H|T], History, [Q|M]) :-
	qdelete(Q, H, T, L1),
	elixir(elx_nodiag(History, Q, 1)),
	queen_2(L1, [Q|History], M).


qdelete(A, A, L, L).
qdelete(X, A, [H|T], [A|R]) :-
	qdelete(X, H, T, R).


nodiag([], _, _).
nodiag([N|L], B, D) :-
	D != N - B,
	D != B - N,
	D1 is D + 1,
	nodiag(L, B, D1).

!elixir

def nodiag([],_,_) do true end
def nodiag([n|l],b,d) do
	if d != n-b && d != b-n do
		nodiag(l,b,d+1)
	else
		false
	end
end