Derived Read instances for recursive datatypes with infix constructors are too inefficient

Consider this definition:

data Exp = C | Exp :+: Exp | Exp :-: Exp deriving ( Read, Show )

Now, try something like:

> read "((((((((((C))))))))))" :: Exp

Even this simple expression may take several seconds to parse. It gets worse if you keep adding parenthesis. And even worse if you add more infix constructors....