Hm, I thought it is a pattern match with constant, as in f ('a':xs) ==

I wonder what you'd make of this definition, then?

    (*) `on` f = \x y -> f x * f y

 

According to the enlightenment above, I'd say (*) is a variable that holds some function/operator that is applied on (f x) and (f y),  not the multiplication, right?