16 Jan
2012
16 Jan
'12
12:32 a.m.
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