Re: Known problems with promoted tuples and lists in GHC 7.4.1?

6 Jun 2012

      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  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  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 
http://www.eyrie.org/~zednenem/
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-- 
Dave Menendez 
http://www.eyrie.org/~zednenem/