[Haskell-cafe] Closed classes

[Imants Cekusins]

This would be very useful indeed.

Can closed type families not be used to achieve the same result even now,
already?

I tried to use type families recently to explicitly pick an (otherwise
overlapping) instance in specified order but could not figure out, how.

If someone could give a complete simple example of primary intended use of
closed type families with class instances,  this would help a lot.
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