#1968: data family + GADT: not implemented yet
---------------------------------------------------+------------------------
Reporter: Remi | Owner: chak
Type: bug | Status: new
Priority: normal | Milestone: 6.10 branch
Component: Compiler (Type checker) | Version: 6.9
Severity: normal | Resolution:
Keywords: data type family GADT choose_univs | Difficulty: Moderate (1
day)
Testcase: GADT13 | Os:
Unknown/Multiple
Architecture: Unknown/Multiple |
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Comment (by simonpj):
Can we be more specific about what this ticket is about? The HEAD (but
not 6.10) does indeed accept GADT syntax for data type families. (I
implemented that a few months ago, but I think I forgot to tell anyone.)
So the following program compiles fine; I believe it meets the hopes
expressed by 'guest' and Wolfgang.
{{{
{-# LANGUAGE GADTs, TypeFamilies, KindSignatures #-}
module Foo where
data family Blah x :: * -> *
data instance Blah Char a where
Char1 :: Blah Char Int
Char2 :: Blah Char Bool
foo :: Blah Char a -> a
foo Char1 = 2
foo Char2 = False
-------------------
class C t where
data D t :: * -> *
instance C Bool where
data D Bool a where
A :: D Bool Int
B :: D Bool Char
}}}
Does that do it? Shall we close the ticket? I've updated the docs to say
explicitly that GADT syntax -- including actually defining a GADT as
Wolfgang wants -- is allowed.
Simon
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/1968#comment:12>
GHC <http://www.haskell.org/ghc/>
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