Pretty printing of kind-involving inferred types

An example of inferred types (foo, bar, both), for brevity's sake omitting value-level details:

{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE KindSignatures #-}
{-# LANGUAGE TypeOperators #-}
import GHC.TypeLits 

data (:::) (sy :: Symbol) ty 
data Key (sy :: Symbol) 
data Rec (rs :: [*])

(*=) :: Key sy -> ty -> Rec '[sy ::: ty]
(*=) = undefined

(.*.) :: (Union xs ys ~ rs) => Rec xs -> Rec ys -> Rec rs
(.*.) = undefined

type family Union (xs :: [*]) (ys :: [*]) :: [*]  where
    Union ((sy ::: t) ': xs) ys = (sy ::: t) ': Union xs ys
    Union '[] ys = ys


fFoo :: Key "foo"
fFoo = undefined

fBar :: Key "bar"
fBar = undefined


foo ::  Rec ((':) * ("foo" ::: [Char]) ('[] *))
foo = fFoo *= "foo"

bar ::  Rec ((':) * ("bar" ::: [Char]) ('[] *))
bar = fBar *= "bar"

both :: Rec ((':) * ("foo" ::: [Char]) ((':) * ("bar" ::: [Char]) ('[] *)))
both = foo .*. bar

There's actually two issues, here: First, the most serious one, GHC prints kind annotations (*) that it can't even parse back, and then [*] types are pretty printed with ': constructors instead of nicely with [,] syntax.

Trac metadata

Trac field	Value
Version	7.7
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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