Hashable instance with random numbers

instance Hashable LeafExpr where
    hash (Var name) = hash "Leaf-Var" + 418871 * hash name
    hash Star = hash "Leaf-Star"
    hash (Const n) = hash "Leaf-Const" + 284551 * n

instance Hashable UnaryOp where
    hash (Neg) = hash "Unary-Neg"
    hash (BinNot) = hash "Unary-BinNot"

instance Hashable BinaryOp where
    hash (Plus) = hash "Binary-Plus"
    hash (Minus) = hash "Binary-Minus"
    hash (Times) = hash "Binary-Times"
    hash (Div) = hash "Binary-Div"
    hash (Mod) = hash "Binary-Mod"

instance Hashable NodeExpr where
    hash (Leaf node) = hash "Leaf" + 770291 * hash node
    hash (Unary op node) = hash "Unary" +
        246509 * hash op +
        845723 * hash node
    hash (Binary op node node') = hash "Binary" +
        1265233 * hash op +
        511013 * hash node +
        1296781 * hash node'