Type family stopped compiling on upgrade from GHC 7.6.3 to 7.8.3

[cheater00 .]

Indeed, I hadn't come to use that at the type level; the original code used
my own types which ended up holding LocalTime; I used Float as a
simplification as it displayed the same weird behaviour.

I guess in the act of randomly walking parseable type family code I have
inadvertently unearthed a bug, which someone else inadvertently fixed,
making me a sort of human QuickCheck.
On 22 Jul 2014 10:57, "Simon Peyton Jones" <simonpj at microsoft.com> wrote:

> I don't know why 7.6.3 accepts it.  'Float' is a valid type but not a
> valid kind.  For it to be a useful kind we'd need float literal at the type
> level, and we have no such thing.  You can use Nat instead, which does
> exist at the type level.
>
> Simon
>
> | -----Original Message-----
> | From: Glasgow-haskell-users [mailto:glasgow-haskell-users-
> | bounces at haskell.org] On Behalf Of cheater00 .
> | Sent: 21 July 2014 18:51
> | To: glasgow-haskell-users at haskell.org
> | Subject: Type family stopped compiling on upgrade from GHC 7.6.3 to
> | 7.8.3
> |
> | Hi, I was experimenting a bit with type families recently and ran into
> | a bit of an issue. Given that I don't know type families that well yet,
> | I was wondering if I made an error somewhere. One thing is that I can't
> | find any relevant changes in the GHC release notes for 7.8.1, .2 or .3.
> |
> | Maybe this code contains an error which 7.6.3 simply wasn't able to
> | find?
> |
> | Thanks.
> |
> | --------
> |
> | -- this code compiles in 7.6.3, but breaks in 7.8.3 with the following
> | message:
> | -- TypeFamilies.hs:14:31:
> | --     ‘End’ of kind ‘*’ is not promotable
> | --     In the kind ‘End’
> | -- In 7.6.3, using :kind!, I can see that the type synonyms contained
> | in the family do work the way I intend them to.
> |
> |
> | {-# Language
> |     GADTs
> |   , TypeFamilies
> |   , DataKinds
> |    #-}
> | module TypeFamilies where
> |
> | data End = Least | Spot Float | Most
> |   deriving (Eq, Show)
> |
> | data Interval = IntervalCons { left :: End, right :: End }
> |   deriving (Eq, Show)
> |
> | type family   Interval2 (a :: End) (b :: End) :: Interval
> | type instance Interval2  Least      Most      =  IntervalCons  Least
> | Most
> | type instance Interval2 (Spot l)    Most      =  IntervalCons (Spot l)
> | Most
> | type instance Interval2  Least     (Spot r)   =  IntervalCons  Least
> | (Spot r)
> | type instance Interval2 (Spot l)   (Spot r)   =  IntervalCons (Spot l)
> | (Spot r)
> | _______________________________________________
> | Glasgow-haskell-users mailing list
> | Glasgow-haskell-users at haskell.org
> | http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
>
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