QueenAttack.fs

module QueenAttack

let create (row, col) =
    row >= 0 && row < 8 && col >= 0 && col < 8

let directions =
    [ (-1, 0)
      (-1, -1)
      (0, -1)
      (1, -1)
      (1, 0)
      (1, 1)
      (0, 1)
      (-1, 1) ]

let step (xDirection, yDirection) (row, col) = 
    (row + xDirection, col + yDirection)

let rec validLine direction position line =
    match create position with
    | false -> line
    | true -> validLine direction (step direction position) (position :: line)

let validMoves position = 
    List.fold 
        (fun moves direction -> validLine direction position moves) 
        []
        directions

let same (x1, y1) (x2, y2) = x1 = x2 && y1 = y2

let underAttack moves position = 
    List.exists (fun move -> same move position) moves

let canAttack queen1 queen2 = underAttack (validMoves queen1) queen2