I thought that might be the case. Thanks for that! Cheers, Reiner On 17/01/2012, at 1:15 AM, Simon Peyton-Jones wrote:
| /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@haskell.org [mailto:glasgow-haskell- | users-bounces@haskell.org] On Behalf Of Reiner Pope | Sent: 16 January 2012 05:32 | To: glasgow-haskell-users@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@haskell.org | http://www.haskell.org/mailman/listinfo/glasgow-haskell-users