Known problems with promoted tuples and lists in GHC 7.4.1?

[Simon Peyton-Jones]

Kind polymorphism and promoted kinds is *not* an advertised feature of 7.4.1.  Much code is there, but it doesn't work when you push it.  The HEAD does work.  If you are using kind polymorphism or promoted kinds, use HEAD (or a development snapshot).

Indeed not_okay compiles fine with HEAD

Simon

| -----Original Message-----
| From: glasgow-haskell-users-bounces at haskell.org [mailto:glasgow-haskell-
| users-bounces at haskell.org] On Behalf Of David Menendez
| Sent: 06 June 2012 23:50
| To: José Pedro Magalhães
| Cc: glasgow-haskell-users at haskell.org Mailing List
| Subject: Re: Known problems with promoted tuples and lists in GHC 7.4.1?
| 
| No, I'm just running 7.4.1.
| 
| Here's a very stripped-down example of what I'm seeing:
| 
| {-# LANGUAGE PolyKinds, DataKinds #-}
| 
| data Pair a b = P a b
| data Nat = Z | S Nat
| 
| data Phantom i = Phantom
| 
| okay :: Phantom ('P Int Int)
| okay = Phantom
| 
| -- not_okay :: Phantom '(Int, Int)
| -- not_okay = Phantom
| 
| Uncommenting that last bit results in this error,
| 
|     Couldn't match kind `BOX' against `*'
|     Kind incompatibility when matching types:
|       k0 :: BOX
|       (*, *) :: *
|     In the expression: Phantom
|     In an equation for `not_okay': not_okay = Phantom
| 
| Something seems to have gone wrong internally.
| 
| 
| On Wed, Jun 6, 2012 at 5:43 PM, José Pedro Magalhães <jpm at cs.uu.nl>
| wrote:
| > Hi David,
| >
| > Are you using HEAD? If so, and you run into problems, please report
| > them (either here or as bugs in trac).
| >
| >
| > Thanks,
| > Pedro
| >
| > On Wed, Jun 6, 2012 at 9:37 PM, David Menendez <dave at zednenem.com>
| wrote:
| >>
| >> Are there any known issues involving type-level pairs and lists? I've
| >> hit a few baffling type errors that went away when I refactored my
| >> code to use locally-defined pairs and lists instead of those provided
| >> by the prelude.
| >>
| >> More worryingly, I had one function that would stop passing the type
| >> checker if I replaced '[n] with (n ': '[]) in its signature.
| >>
| >> --
| >> Dave Menendez <dave at zednenem.com>
| >> <http://www.eyrie.org/~zednenem/>
| >>
| >> _______________________________________________
| >> Glasgow-haskell-users mailing list
| >> Glasgow-haskell-users at haskell.org
| >> http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
| >
| >
| 
| 
| 
| --
| Dave Menendez <dave at zednenem.com>
| <http://www.eyrie.org/~zednenem/>
| 
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