TypeApplications allows instantiation of implicitly-quantified kind variables
TypeApplications doesn't allow unticked list constructor even when it is unambiguous:
GHCi, version 8.0.1: http://www.haskell.org/ghc/ :? for help
> :set -XDataKinds
> :set -XTypeApplications
> :set -XScopedTypeVariables
> :set -XKindSignatures
> let foo :: forall (xs :: [Nat]). (); foo = ()
> foo @'[0]
()
> foo @[0]
<interactive>:17:6: error:
* Expected kind `[Nat]', but `[0]' has kind `*'
* In the type `[0]'
In the expression: foo @[0]
In an equation for `it': it = foo @[0]
<interactive>:17:7: error:
* Expected a type, but `0' has kind `Nat'
* In the type `[0]'
In the expression: foo @[0]
In an equation for `it': it = foo @[0]
why [0] has kind * here?
However this is legal:
> let foo :: forall (x :: Bool). (); foo = ()
> foo @True
()
> foo @'True
()
and this is wierd:
> :set -XPolyKinds
> let foo :: forall (x :: k). (); foo = ()
> foo @'True
<interactive>:12:6: error:
* Expected a type, but 'True has kind `Bool'
* In the type `True'
In the expression: foo @True
In an equation for `it': it = foo @True
> foo @True
<interactive>:13:6: error:
* Expected a type, but 'True has kind `Bool'
* In the type `True'
In the expression: foo @True
In an equation for `it': it = foo @True
Trac metadata
| Trac field | Value |
|---|---|
| Version | 8.0.1 |
| Type | Bug |
| TypeOfFailure | OtherFailure |
| Priority | normal |
| Resolution | Unresolved |
| Component | Compiler |
| Test case | |
| Differential revisions | |
| BlockedBy | |
| Related | |
| Blocking | |
| CC | |
| Operating system | |
| Architecture |
Edited by Adam Gundry