Hugs for Macs different from Hugs for Suns ??

Using the type definition: data Term a = T a [Term a] I run the precomplied Hugs version on a Mac and another one under Sun OS. The first accepts the instance definition: instance Show (Term String) where .. The second reports syntax error in instance head (variable expected) and accepts if I write: instance Show a => Show (Term a) where .. Why do the systems react differently??? Best regards, Peter --- Peter Padawitz Informatik 5 University of Dortmund D-44221 Dortmund Germany phone +49-231-755-5108 fax +49-231-755-4851 or -5802 secretary +49-231-755-5801 email peter.padawitz@udo.edu