enum E { A(A), B(B), } ```

EnumError

```rust

[macro_use]

extern crate procedurals; use std::{io, fmt};

[derive(Debug, EnumError)] // EnumError derives From<*>, fmt::Display and error::Error

pub enum Error { IO(io::Error), Fmt(fmt::Error), } ```

NewType

```rust

[macro_use]

extern crate procedurals;

struct B {}

[derive(NewType)] // NewType derives From, Into, Deref, and DerefMut