:kind command allows unsaturated type family,

data A = B

type family
  F a where
  F B = String

infixr 9 `Compose`
class    (f (g x)) => (f `Compose` g) x
instance (f (g x)) => (f `Compose` g) x

GHCi accepts

ghci> :kind Compose Eq F
Compose Eq F :: A -> Constraint

but when used in code it gets rejected

-- tvI6.hs:13:8-33: error: …
--     • The type family ‘F’ should have 1 argument, but has been given none
--     • In the type signature:
--         foo :: (Eq `Compose` F) a => String
-- Compilation failed.
foo :: (Eq`Compose`F) a => String
foo = undefined 

Bug? Version 8.0.0.20160511

Trac metadata

Trac field	Value
Version	8.0.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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