| I want to define something like
|     class (Eq (forall a. T a), Monad T) => C T
| where the context shall mean that T has to be an instance of Monad and
| that for every type a the type T a has to be an instance of Eq.
| Is such a thing possible with some Haskell implementation?

Not currently, but I think it makes sense, and I'll implement it if
enough people ask.

Presumably you mean 'instance' not 'class'?  A class decl always has a
type variable after the =>; thus ...=> C a.

There aren't many type constructors T for which T a is an equality
type...

Simon
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