> On Apr 6, 2021, at 7:44 AM, Anthony Clayden <anthony_clay...@clear.net.nz>
> wrote:
>
> > But why does this matter?
>
> Because I want the semantics of that equality constraint, without switching
> on any of these, which I don't otherwise use:
>
> GADTs
> TypeFamilies
> TypeOperators
>
> And if that means I can't use infix `~` in my constraints, I'll put up with
> that. (I'd user-define a conventional class, say `TypeCast`. Could be that
> has to be defined in terms of `~`, in which case I'd put that in a shim
> module as the only place with those extensions.)
>
A shim module would work for you here, indeed.
Individuals' opinions of extensions will differ, but TypeOperators is much less
powerful than either of the others: it affects only parsing, and in a fully
backward-compatible way.
Richard
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