module QueenAttack

let allowed pos = pos > -1 && pos < 8

let create (position: int * int) =
    match position with
    | (r, c) when allowed r && allowed c -> true
    | _ -> false

let difference a b = abs (a - b) 

let diagonallyAttacked (a: int * int) (b: int * int) = 
    let cmpARow = a |> fst |> difference 
    let cmpACol = a |> snd |> difference
    (b |> fst |> cmpARow) = (b |> snd |> cmpACol)

let canAttack (queen1: int * int) (queen2: int * int) = 
    (=) (queen1 |> fst) (queen2 |> fst) ||
    (=) (queen1 |> snd) (queen2 |> snd) ||
    diagonallyAttacked queen1 queen2