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 |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | |
Operating system | |
Architecture |