/* A program to solve the 8-queens problem */

let
  var N := 8

  type intArray = array of int

  var row := intArray [ N ] of 0
  var col := intArray [ N ] of 0
  var diag1 := intArray [N+N-1] of 0
  var diag2 := intArray [N+N-1] of 0

  function printboard() = (
    for i := 0 to N-1 do (
      for j := 0 to N-1 do print(if col[i]=j then " O" else " .");
      print("\n")
    );
    print("\n")
  )

  function try(c:int) = (
    /*  for i:= 0 to c do print("."); print("\n"); flush();*/
    if c=N
    then printboard()
    else
      for r := 0 to N-1
      do
        if row[r]=0 & diag1[r+c]=0 & diag2[r+7-c]=0
        then (
          row[r]       := 1;
          diag1[r+c]   := 1;
          diag2[r+7-c] := 1;
          col[c]       := r;
          try(c+1);
          row[r]       := 0;
          diag1[r+c]   := 0;
          diag2[r+7-c] := 0
        )
  )
in
  try(0)
end