Can we offer ~ without GADTs or type families?

[Ryan Scott]

Hi David,

> Could we get a separate LANGUAGE pragma just for equality constraints?

I think we should, and I don't think we'd even need to introduce a new
pragma, since there's already a perfectly good one: -XTypeOperators!
After all, there's nothing really that special about (~) other than
some typechecking details. A fix to Trac #9194 [1] would give us this.

Ryan S.
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[1] https://ghc.haskell.org/trac/ghc/ticket/9194