5 instance Additive E where
7 E a + E b = E ("(" + a + "+" + b + ")")
11 neg (E a) = E ("(-" + a + ")")
12 E a - E b = E ("(" + a + "-" + b + ")")
13 E a * E b = E ("(" + a + "*" + b + ")")
14 fromInteger x = E (show x)
23 main = eToString (-a + b + (-c*d))