「エイト・クイーン問題」をErlangで ref: http://qiita.com/pazworld/items/2a50f208ca2e5c1b4098

eq.erl

% solve 8-queens problem.

-module(eq).
-compile(export_all).

solve() ->
  register(counter, spawn(fun() -> counter(0) end)),
  solve(cols(), []),
  counter ! show.

cols() -> [1,2,3,4,5,6,7,8].

solve(_, Queens) when length(Queens) == 8 -> display(Queens);

solve([], _) -> ok;

solve([Col|T], Queens) ->
  case not conflict(Col, Queens) of
    true  -> solve(cols(), [Col | Queens]);
    false -> ok
  end,
  solve(T, Queens).

conflict(Col, Queens) ->
  Conflict = fun({N, QCol}) -> Col == QCol orelse abs(Col - QCol) == N end,
  lists:any(Conflict, with_idx(Queens)).

with_idx(L) -> lists:zip(lists:seq(1, length(L)), L).

display(Queens) ->
  counter ! countup,
  Frame = "**********",
  io:fwrite("~s~n", [Frame]),
  lists:foreach(fun(X) -> io:fwrite("*~s*~n", [make_line(X)]) end, Queens),
  io:fwrite("~s~n~n", [Frame]).

make_line(X) -> string:chars($., X - 1) ++ "Q" ++ string:chars($., 8 - X).

counter(N) ->
  receive
    countup -> counter(N + 1);
    show    -> io:fwrite("Count: ~w~n", [N])
  end.