constraints inside classes

[Simon Peyton-Jones]

OK, OK. I give in! 

I've lifted this restriction in the HEAD.  

Simon

| -----Original Message-----
| From: Marcin 'Qrczak' Kowalczyk [mailto:qrczak at knm.org.pl] 
| Sent: 24 February 2002 08:02
| To: glasgow-haskell-bugs at haskell.org
| Subject: Re: constraints inside classes
| 
| 
| Fri, 22 Feb 2002 12:55:13 -0800, Mark P Jones <mpj at cse.ogi.edu> pisze:
| 
| > | class Foo a where
| > |         f :: Eq a => a -> Bool
| > 
| > This behavior of Hugs is intentional, and is documented as 
| a non-bug 
| > on the Hugs web pages:  (right at the end)
| > 
| >   http://cvs.haskell.org/Hugs/pages/bugsandfeatures.htm
| > 
| > I don't know how the "non bug" status was determined, but 
| perhaps it 
| > reflects a view that the real bug is in the language 
| report, where a 
| > demonstrably unnecessary, and potentially limiting restriction is 
| > imposed.
| 
| It's indeed limiting and IMHO should be removed; I have told 
| about it some time ago. Here is a stripped-down example where 
| it's necessary:
| 
| class Seq s a where
|     fromList :: [a] -> s a
|     elem     :: Eq a => a -> s a -> Bool
| 
| I've seen attempts at expressing such class with features 
| that GHC allows but they were all wrong.
| 
| -- 
|  __("<  Marcin Kowalczyk * qrczak at knm.org.pl 
| http://qrczak.ids.net.pl/  \__/
|   ^^
| QRCZAK
| 
| 
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