import Html exposing (text)

sqrt : Float -> Float
sqrt x =
   if x >= 0 then
      sqrt_iter 1 x
   else
      -1
      
sqrt_iter : Float -> Float -> Float
sqrt_iter guess x =
   if good_enough guess x then
      guess
   else
      sqrt_iter (improve guess x) x

good_enough : Float -> Float -> Bool
good_enough guess x = abs (square guess - x) < 0.001

square : Float -> Float
square x = x * x

average : Float -> Float -> Float
average x y = (x + y) / 2

improve : Float -> Float -> Float
improve guess x = average guess (x/guess)


main =
  text (toString (sqrt 16))