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T4254b.hs:10:10: error: [GHC-25897]
• Couldn't match type ‘b’ with ‘Bool’
arising from a functional dependency between constraints:
‘FD Int Bool’
arising from a type ambiguity check for
the type signature for ‘fails’ at T4254b.hs:10:10-48
‘FD Int b’
arising from the type signature for:
fails :: forall a b.
(a ~ Int, FD a b) =>
a -> Bool at T4254b.hs:10:10-48
‘b’ is a rigid type variable bound by
the type signature for:
fails :: forall a b. (a ~ Int, FD a b) => a -> Bool
at T4254b.hs:10:10-48
• In the ambiguity check for ‘fails’
To defer the ambiguity check to use sites, enable AllowAmbiguousTypes
In the type signature:
fails :: forall a b. (a ~ Int, FD a b) => a -> Bool
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