[Haskell-cafe] Typeclasses and instances

[Simon Peyton-Jones]

I've finally gotten around to fixing this.  The fix won't be in 6.4
(ever) as mentioned below, but it's done in the HEAD.

Simon

| -----Original Message-----
| From: haskell-cafe-bounces at haskell.org
[mailto:haskell-cafe-bounces at haskell.org] On Behalf Of
| Simon Peyton-Jones
| Sent: 18 March 2005 13:01
| To: Mark Carroll; haskell-cafe at haskell.org
| Subject: RE: [Haskell-cafe] Typeclasses and instances
| 
| Strange.  This is a bug in GHC that crept in when I implemented GADTs.
| It turns out to be slightly structural; fixing it will change the
| interface-file format.  So it won't get fixed in 6.4; but will in the
| HEAD.    That doesn't bother me; the context on a data/newtype decl is
a
| strange thing anyway; only useful for generating extra errors...   but
| yes, it's a bug thanks for pointing it out.
| 
| Simon
| 
| | -----Original Message-----
| | From: haskell-cafe-bounces at haskell.org
| [mailto:haskell-cafe-bounces at haskell.org] On Behalf Of Mark
| | Carroll
| | Sent: 17 March 2005 19:58
| | To: haskell-cafe at haskell.org
| | Subject: Re: [Haskell-cafe] Typeclasses and instances
| |
| | Another note, with more help from friends:
| |
| | It turns out that GHC 6.4 will let me do,
| |
| | 	newtype Floating a => Test a = Test [a] deriving Show
| |
| | 	x = Test [False, True]
| |
| | but, if I change "newtype" to "data", it then says,
| |
| | 	No instance for (Floating Bool)
| |
| | I'm not sure I quite understand what's going on.
| |
| | -- Mark
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