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T15883b.hs:14:1: error:
• Ambiguous type variable ‘a0’ arising from a use of ‘==’
prevents the constraint ‘(Eq a0)’ from being solved.
Probable fix: use a type annotation to specify what ‘a0’ should be.
Potentially matching instances:
instance Eq SpecConstrAnnotation -- Defined in ‘GHC.Exts’
instance Eq Ordering -- Defined in ‘GHC.Classes’
...plus 25 others
...plus four instances involving out-of-scope types
(use -fprint-potential-instances to see them all)
• In the expression: a1 == b1
In an equation for ‘==’: (==) (MkFoo a1) (MkFoo b1) = ((a1 == b1))
When typechecking the code for ‘==’
in a derived instance for ‘Eq (Foo LiftedRep)’:
To see the code I am typechecking, use -ddump-deriv
In the instance declaration for ‘Eq (Foo LiftedRep)’
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