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.

PureScript is mentioned on one of his slides.

It's 9:30pm CET.

The sun set a while ago ...

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