How about this, I found it bt myself: data TupleList (t :: **) = TupleNil | TupleUnit t (TupleList t) fstL :: TupleList (a -> **) -> a fstL TupleNil = error "TupleList2 is TupleNil" fstL (TupleUnit a _ ) = a sndL :: TupleList (* -> a -> **) -> a sndL TupleNil = error "TupleList2 is TupleNil" sndL (TupleUnit a TupleNil ) = error "TupleList2 is TupleUnit a TupleNil" sndL (TupleUnit _ (TupleUnit a _ ) ) = a headL :: TupleList (a -> **) -> a headL TupleNil = error "TupleList2 is TupleNil" headL (TupleUnit a _ ) = a tailL :: TupleList (* -> a) -> a tailL TupleNil = error "TupleList2 is TupleNil" tailL (TupleUnit _ a ) = a instance Functor (TupleList (a :: **)) where fmap _ TupleNil = TupleNil fmap f (TupleUnit x xs) = TupleUnit (f x) (fmap xs) tupleL :: TupleList ( (Int :: *) -> (String :: *) -> (Bool :: *) ) tupleL = TupleUnit 5 (TupleUnit "inside tuple" (TupleUnit True TupleNil))) fstTuppleL :: Int fstTuppleL = fstL tupleL -- = 2 sndTuppleL :: String sndTuppleL = sndL tupleL -- = "inside tuple" tlTuppleL :: TupleList ( (String :: *) -> (Bool :: *) ) tlTuppleL = tailL tupleL -- = TupleUnit "inside tuple" (TupleUnit True TupleNil)) cheers, Wvv 31 Jul 2013 at 22:48:19, Roman Cheplyaka-2 [via Haskell] (ml-node+s1045720n5733671h40@n5.nabble.com) wrote: That's because types that belong to most non-star kinds cannot have values. data Foo (a :: k) = Foo is okay, data Foo (a :: k) = Foo a is bad because there cannot be a field of type a :: k. So no, no useful examples exist, because you wouldn't be able to use such a data constructor even if you could declare it. Roman * Wvv <[hidden email]> [2013-07-31 11:40:17-0700]
OMG! I still have 7.6.3. It has old Typeable.
I misunderstood PolyKinds a bit. It looks like k /= **, k ~ *******...
But we cannot use "CloseKinds" like
data Foo (a::k) = Foo a -- catch an error "Expected kind `OpenKind', but `a' has kind `k'"
with RankNKinds we could write: data Foo (a::**) = Foo a data Bar (a::***) = Bar a
So, now the task is more easy: I'm asking for useful examples with "CloseKinds" with ** and higher, and any useful examples for *** and higher
cheers, Wvv
29 Jul 2013 at 14:44:50, José Pedro Magalhães [via Haskell] ([hidden email]) wrote:
Hi,
On Fri, Jul 26, 2013 at 10:42 PM, Wvv <[hidden email]> wrote:
First useful use is in Typeable. In GHC 7.8 class Typeable (a::k) where ... <<==>> class Typeable (a ::**) where ...
But we can't write data Foo (a::k)->(a::k)->* ... deriving Typeable
Why not? This works fine in 7.7, as far as I know.
Cheers, Pedro
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