quadratic_equation_kata.ml

open Core_kernel.Std

module QuadraticEquation = struct
  open Float

  type t = {a: float; b: float; c: float}

  let discriminant {a; b; c} = b * b - 4.0 * a * c

  let root {a; b; c} discriminant (+/-) =
    (-1.0 * b +/- sqrt discriminant) / 2.0 * a

  let solve ({a; b; c} as coefficients) =
    let d = discriminant coefficients in
    let root = root coefficients d in
    match sign d with
    | Sign.Neg  -> `None
    | Sign.Zero -> `One (root (+))
    | Sign.Pos  -> `Two (root (+), root (-))
end

let () =
  let open QuadraticEquation in
  assert (solve {a=1.0; b=(-1.0); c=(-2.0)} = `Two (2.0, -1.0));
  assert (solve {a=1.0; b=(-6.0); c=9.0} = `One 3.0);
  assert (solve {a=3.0; b=4.0; c=2.0} = `None);
  print_endline "ok"