GADT declaration not (yet) handled by Template Haskell

Compiling this:

{-# LANGUAGE TemplateHaskell, GADTs #-}
module GadtBug where

$([d|data T a where { T :: T Char; }|])

gives this:

GadtBug.hs:4:23:
    GADT declaration not (yet) handled by Template Haskell T :: T Char

Trac metadata

Trac field	Value
Version	7.0.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler (Type checker)
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture

changed weight to 5

added Tbug Trac import typechecker labels

mentioned in commit b47643f5

mentioned in commit 5c4a4c4b

closed

I've fixed this. I did not need to extend TH syntax, because it's already rich enough to do the job (cf #4188 (closed)).

commit 5c4a4c4bfe2a007f41f42ebab689bcd7219bed0d
Author: Simon Peyton Jones <simonpj@microsoft.com>
Date:   Sat Jun 11 16:44:07 2011 +0100

    Make TH capable of quoting GADT declarations (Trac #5217)
    
    Template Haskell doesn't support GADTs directly but
    we can use equality constraints to do the job. Here's
    an example of the dump from splicing such a declaration:
    
        [d| data T a b
                where
                  T1 :: Int -> T Int Char
                  T2 :: a -> T a a
                  T3 :: a -> T [a] a
                  T4 :: a -> b -> T b [a] |]
      ======>
        T5217.hs:(6,3)-(9,53)
        data T a[aQW] b[aQX]
            = (b[aQX] ~ Char, a[aQW] ~ Int) => T1 Int |
              b[aQX] ~ a[aQW] => T2 a[aQW] |
              a[aQW] ~ [b[aQX]] => T3 b[aQX] |
              forall a[aQY]. b[aQX] ~ [a[aQY]] => T4 a[aQY] a[aQW]

 compiler/deSugar/DsMeta.hs      |  110 +++++++++++++++++++++++++++++----------
 compiler/hsSyn/HsTypes.lhs      |   14 +++++
 compiler/typecheck/TcHsType.lhs |   19 +------
 compiler/typecheck/TcMType.lhs  |    5 +-
 4 files changed, 102 insertions(+), 46 deletions(-)

Trac metadata

Trac field	Value
Resolution	Unresolved → ResolvedFixed
Test case	→ th/T5217

mentioned in issue #10828 (closed)

#10828 (closed) extends TH syntax to support GADTs without encoding them as normal data types.

Trac metadata

Trac field	Value
Related	- → #10828 (closed)

changed milestone to %8.0.1

added Pnormal label