Manage unsafe coercions more carefully #115
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Instead of using `Any`, use `TypeRep Any` or `f Any`. This makes it considerably easier to see what each coercion is actually doing. It also allows the compiler to use more type information around the unsafe coercions. For example, `Const a b` and `Const a Any` are representationally the same, so converting between them should be able to compile to a *safe* coercion (better for optimization). This doesn't happen in GHC 9.0, but I think that may have been fixed in 9.2.
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Instead of using
Any, useTypeRep Anyorf Any. This makes itconsiderably easier to see what each coercion is actually doing. It
also allows the compiler to use more type information around the unsafe
coercions. For example,
Const a bandConst a Anyarerepresentationally the same, so converting between them should be able
to compile to a safe coercion (better for optimization). This doesn't
happen in GHC 9.0, but I think that may have been fixed in 9.2.