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Simon Peyton Jones authored
Previously (Trac #10351) we could get Non type-variable argument in the constraint: C [t] (Use FlexibleContexts to permit this) When checking that `f' has the inferred type f :: forall t. C [t] => t -> () which is a bit stupid: we have *inferred* a type that we immediately *reject*. This patch arranges that that the generalisation mechanism (TcSimplify.decideQuantification) doesn't pick a predicate that will be rejected by the subsequent validity check. This forced some minor refactoring, as usual.
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