There 100% are unit systems implemented with types. (One example: https://github.com/goldfirere/units/tree/master/units)

Structural types does not preclude having some names that prevent mix-ups. Haskell’s `data` keyword doesn’t let you confuse structurally-identical things.

> If someone encodes "RGBColor" and "LinearRGBColor", both structs with 3 floats, your type system wouldn't provide any errors if a LinearRGB color is passed into an RGB calculation.

It 100% would, unless you were silly enough to use a bare tuple to do it. Again, defining a type with `data` in Haskell wouldn’t get confused.