DefaultSignatures and MultiParamTypeClasses

[Simon Peyton-Jones]

| /tmp/Test.hs:4:1:	
|     The multi-parameter class `C' cannot have generic methods
|     In the class declaration for `C'

Aha.  Trawling the commit logs, this test is simply a vestige of the PREVIOUS generic-class story, now long gone.  So we can lift the restriction easily.

I'll commit a patch shortly; I hope it'll be in time for 7.4

Simon

| -----Original Message-----
| From: glasgow-haskell-users-bounces at haskell.org [mailto:glasgow-haskell-
| users-bounces at haskell.org] On Behalf Of Reiner Pope
| Sent: 16 January 2012 05:32
| To: glasgow-haskell-users at haskell.org
| Subject: DefaultSignatures and MultiParamTypeClasses
| 
| Hi all,
| 
| I just tried, and it appears that the new DefaultSignatures extension doesn't
| work with multi parameter type classes. For example, when I compile this
| file:
| 
| ----
| {-# LANGUAGE DefaultSignatures, MultiParamTypeClasses #-}
| module Test where
| 
| class C a b where
|   conv :: a -> b
| 
|   default conv :: D a b => a -> b
|   conv = dconv
| 
| class D a b where
|   dconv :: a -> b
| -----
| 
| I get the error message:
| 
| -----
| /tmp/Test.hs:4:1:	
|     The multi-parameter class `C' cannot have generic methods
|     In the class declaration for `C'
| Failed, modules loaded: none.
| -----
| 
| Is there a reason for this restriction, or is it merely an accident?
| 
| Cheers,
| Reiner
| _______________________________________________
| Glasgow-haskell-users mailing list
| Glasgow-haskell-users at haskell.org
| http://www.haskell.org/mailman/listinfo/glasgow-haskell-users