Reflecting on Haskell in 2015 11 years ago
distance :: { x :: Number, y :: Number } -> Number
distance point = sqrt(point.x^2 + point.y^2)
The function application of sqrt shouldn't have parens.
And the type of distance should be
distance :: forall r. { x :: Number, y :: Number | r} -> Number
Otherwise, it's not row-polymorphic and you wouldn't be able to apply distance to a record of type Point3D.