[ ghc-Bugs-1116210 ] GADT constructor constraints ignored

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Bugs item #1116210, was opened at 2005-02-04 09:28
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Category: Compiler (Type checker)
Group: 6.4
Status: Open
Resolution: None
Priority: 5
Submitted By: Wolfram Kahl (wolfram_kahl)
Assigned to: Nobody/Anonymous (nobody)
Summary: GADT constructor constraints ignored

Initial Comment:
Class constraints on GADT constructore appear to be
ignored.

I tried:

data Expr :: * -> * where
  Const :: Show a => a -> Expr a
  Apply :: Fct a b -> Expr a -> Expr b

and there is no way to define the expected constraint-less
Show instance --- for details, see Expr0.lhs.

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