[Haskell-cafe] Rank N Kinds
vitea3v at rambler.ru
Wed Jul 31 21:56:03 CEST 2013
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))
31 Jul 2013 at 22:48:19, Roman Cheplyaka-2 [via Haskell]
(ml-node+s1045720n5733671h40 at n5.nabble.com) wrote:
That's because types that belong to most non-star kinds cannot have
data Foo (a :: k) = Foo
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.
* Wvv <[hidden email]> [2013-07-31 11:40:17-0700]
> 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
> 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
> useful examples for *** and higher
> cheers, Wvv
> 29 Jul 2013 at 14:44:50, José Pedro Magalhães [via Haskell]
> ([hidden email]) wrote:
> 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.
> View this message in context:
> Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.
> Haskell-Cafe mailing list
> [hidden email]
Haskell-Cafe mailing list
View this message in context: http://haskell.1045720.n5.nabble.com/Rank-N-Kinds-tp5733482p5733672.html
Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.
-------------- next part --------------
An HTML attachment was scrubbed...
More information about the Haskell-Cafe