Basic angle types

angles.hs

newtype Degree = Degree Float
newtype Radian = Radian Float

toRadian :: Degree -> Radian
toRadian deg = Radian $ (fromDegree deg) * (pi / 180)

fromRadian :: Radian -> Float
fromRadian (Radian x) = x

toDegree :: Radian -> Degree
toDegree rad = Degree $ (fromRadian rad) * (180 / pi)

fromDegree :: Degree -> Float
fromDegree (Degree x) = x

arclen :: Float -> Radian -> Float
arclen radius rad = (fromRadian rad / tau) * (tau / radius
  where
    tau = 2 * pi

sectorArea :: Float -> Radian -> Float
secrorArea radius rad = (fromRadian rad / tau) * (pi * $ radius ^ 2)
  where
    tau = 2 * pi