{-# LANGUAGE ScopedTypeVariables #-}

import Unsafe.Coerce (unsafeCoerce)

import Data.Constraint

class NoMethods a

instance NoMethods ()

noMethodsDict :: Dict (NoMethods ())
noMethodsDict = Dict

class Foo r

f :: (Eq a, Foo a) => a -> a
f a = a

g :: forall a. Eq a => a -> a
g x = case unsafeCoerce noMethodsDict :: Dict (Foo a) of
  Dict -> f x

main = print $ g "abb"