What version of the GHC code are you looking at? The parser is currently stored
in compiler/parser/Parser.y.pp (note the pp) and doesn’t have these lines. As
far as I know, there is no way to refer to OpenKind from source.
You’re absolutely right about the type of `undefined`. `undefined` (and
`error`) have magical types. GHC knows that GHC.Err defines an `undefined`
symbol and gives it its type by fiat. There is no way (I believe) to reproduce
this behavior.
If you have -fprint-explicit-foralls and -fprint-explicit-kinds enabled,
quantified variables of kind * are not given kinds in the output. So, the lack
of a kind annotation tells you that `a`’s kind is *. Any other kind (assuming
these flags) would be printed.
I hope this helps!
Richard
On Apr 15, 2014, at 7:39 PM, Conal Elliott <co...@conal.net> wrote:
> I see ‘#’ for unlifted and ‘?’ for open kinds in compiler/parser/Parser.y:
> akind :: { IfaceKind }
> : '*' { ifaceLiftedTypeKind }
> | '#' { ifaceUnliftedTypeKind }
> | '?' { ifaceOpenTypeKind }
> | '(' kind ')' { $2 }
>
> kind :: { IfaceKind }
> : akind { $1 }
> | akind '->' kind { ifaceArrow $1 $3 }
> However, I don’t know how to get GHC to accept ‘#’ or ‘?’ in a kind
> annotation. Are these kinds really available to source programs.
>
> I see that undefined has an open-kinded type:
>
> *Main> :i undefined
> undefined :: forall (a :: OpenKind). a -- Defined in ‘GHC.Err’
> Looking in the GHC.Err source, I just see the following:
>
> undefined :: a
> undefined = error "Prelude.undefined"
> However, if I try similarly,
>
> q :: a
> q = error "q"
> I don’t see a similar type:
>
> *X> :i q
> q :: forall a. a -- Defined at ../test/X.hs:12:1
>
> I don't know what kind 'a' has here, nor how to find out.
>
> -- Conal
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