parsing differences

[Justin Cormack]

Hugs will happily accept definitions such as:
(f `cross` g) (x, y) = (f x , g y)
while ghc gives
parse error on input: "cross"

It is not that ghc doesn't like any definition with `` on the left, as
x `op` y = x + y is fine, it just seems to be cases with brackets.

It is not entirely clear from the language spec whether or not this is valid,
but it does seem more consistent to allow this.

Justin Cormack