instance inference

[Simon Peyton-Jones]

Interesting example.  Yes, GHC builds recursive dictionaries these days.
There's a bit of discussion in our SYB paper in ICFP'05.
http://research.microsoft.com/%7Esimonpj/papers/hmap/ 	And Martin
Sulzmann has a whole paper about this point.
http://www.comp.nus.edu.sg/~sulzmann/  ("Co-induction...")

Simon

| -----Original Message-----
| From: glasgow-haskell-users-bounces at haskell.org
[mailto:glasgow-haskell-users-
| bounces at haskell.org] On Behalf Of Ross Paterson
| Sent: 12 December 2005 10:46
| To: glasgow-haskell-users at haskell.org
| Subject: instance inference
| 
| I'm puzzled that the following is accepted.  Is some sort of greatest
| fixed point computation used for instances?
| 
| {-# OPTIONS_GHC -fglasgow-exts #-}
| module M where
| 
| class C a b where c :: a -> b -> Bool
| 
| instance C b b => C (Maybe a) b where c x y = c y y
| 
| f :: Maybe a -> Bool
| f x = c x x
| 
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