Find constraints over type

[Alejandro Serrano Mena]

Dear GHC devs,
I am trying to figure out a way to obtain the constraints that hold over a
type. Let me give you an example: suppose that I write the following
function:

f :: Eq a => [a] -> Bool
f xs = xs == []

If I ask for the type of the Var ' xs', I get back '[a]'. This is correct,
but I am missing the crucial information that '[a]' must be Eq.

Is there an easy way to get it? It seems that 'varType' doesn't give me
enough information.

Regards,
Alejandro
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