tcfail208.hs:4:10: error:
• Could not deduce (Eq (m a)) arising from a use of ‘==’
from the context: (Monad m, Eq a)
bound by the type signature for:
f :: (Monad m, Eq a) => a -> m a -> Bool
at tcfail208.hs:3:1-40
• In the expression: (return x == y)
In an equation for ‘f’: f x y = (return x == y)