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T13651.hs:12:8: error: [GHC-25897]
• Could not deduce ‘cr ~ Bar h (Foo r)’
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:(12,8)-(14,65)
‘cr’ is a rigid type variable 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:(12,8)-(14,65)
• 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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