This patch implements the Clean up printing of foralls proposal:
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Whenever printing variables quantified in a forall, print inferred variables with braces.
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Maximally instantiate any inferred or dictionary arguments (class constraints) to expressions passed to :type
It also addresses a part of #16320. Specifically, it adds two more
conditions to the predicate that decides if foralls should be
printed. GHC will now print foralls if any of these is also true:
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The foralls are not all at the top. Exception: foralls are allowed to be mixed with class constraints, but no foralls can appear under a proper ->.
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Two quantified type variables are spelled the same
It does not address Inefficient implementation of eliminateRuntimeReps and Extremely confusing swizzling of foralls and contexts yet.