On Sun, Jul 13, 2025 at 11:47:36AM +0100, Tom Ellis wrote:

...

* There is, however, a known trick. This works: *>

Ah yes. Same solution here https://discourse.haskell.org/t/how-to-use-requiredtypearguments-with-typecl... Currently, `RequiredTypeArguments` is documented as " only partially implemented in GHC". Full specification to be found in proposal #281. That proposal doesn't give examples of how to write instances for `sizeOf`, as and when we get Dependent Haskell in full. Will it still need the type equality trick?

* (But I prefer your [Viktor's] solution: the wrapper.)*

*>* Yes. That in effect still uses a term-level proxy for the type, as argument to _sizeOf. For example I could go pattern Bool :: Bool pattern Bool = undefined ... _sizeOf Bool ...