T8450.hs:8:7: error:
• Couldn't match expected type ‘a’ with actual type ‘()’
‘a’ is a rigid type variable bound by
the type signature for:
run :: forall a. a
at T8450.hs:7:1-18
• In the expression: runEffect $ (undefined :: Either a ())
In an equation for ‘run’:
run = runEffect $ (undefined :: Either a ())
• Relevant bindings include run :: a (bound at T8450.hs:8:1)