13 Jan
2004
13 Jan
'04
7:24 p.m.
John Tromp wrote:
instance (Bar a) => Foo a
I have tried to write code myself like in the last line, stating that any instance of one class should also be an instance of another class. But Hugs would complain about it.
You're right. Hugs needs to be told that the code is in an extended Haskell, with popular extensions. Therefore, Hugs has to invoked as "hugs -98". It seems -98 flag cannot be changed once the Hugs is running. Incidentally, the previously posted code included rank-2 types -- which are flagrantly not in Haskell98. Therefore, without -98 flag, Hugs will have a lot to complain about.