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T7279.hs:6:10: error:
• Could not deduce (Show b0)
from the context: (Eq a, Show b)
bound by an instance declaration:
forall a b. (Eq a, Show b) => Eq (T a)
at T7279.hs:6:10-35
The type variable ‘b0’ is ambiguous
Potentially matching instances:
instance Show Ordering -- Defined in ‘GHC.Show’
instance Show a => Show (Maybe a) -- Defined in ‘GHC.Show’
...plus 25 others
...plus 12 instances involving out-of-scope types
(use -fprint-potential-instances to see them all)
• In the ambiguity check for an instance declaration
To defer the ambiguity check to use sites, enable AllowAmbiguousTypes
In the instance declaration for ‘Eq (T a)’
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