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T13651.hs:11:8: error:
• Could not deduce: F cr (Bar (Foo h) (Foo u)) ~ Bar h (Bar r u)
from the context: (F cr cu ~ Bar h (Bar r u),
F cu cs ~ Bar (Foo h) (Bar u s))
bound by the type signature for:
foo :: forall cr cu h r u cs s.
(F cr cu ~ Bar h (Bar r u), F cu cs ~ Bar (Foo h) (Bar u s)) =>
Bar h (Bar r u) -> Bar (Foo h) (Bar u s) -> Foo (cr -> cs)
at T13651.hs:(11,8)-(13,65)
• In the ambiguity check for ‘foo’
To defer the ambiguity check to use sites, enable AllowAmbiguousTypes
In the type signature:
foo :: (F cr cu ~ Bar h (Bar r u),
F cu cs ~ Bar (Foo h) (Bar u s)) =>
Bar h (Bar r u) -> Bar (Foo h) (Bar u s) -> Foo (cr -> cs)
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