T9109.hs:8:13: error:
• Couldn't match expected type ‘p’ with actual type ‘Bool’
‘p’ is untouchable
inside the constraints: a ~ Bool
bound by a pattern with constructor: GBool :: G Bool,
in an equation for ‘foo’
at T9109.hs:8:5-9
‘p’ is a rigid type variable bound by
the inferred type of foo :: G a -> p at T9109.hs:8:1-16
Possible fix: add a type signature for ‘foo’
• In the expression: True
In an equation for ‘foo’: foo GBool = True
• Relevant bindings include foo :: G a -> p (bound at T9109.hs:8:1)