Static check enum as type annotation

```rust
enum Color {
 Red = "#FF0000",
 Green = "#00FF00",
 Blue = "#0000FF",
}

fn get_color(color: Color) -> str {
 match color {
 Color::Red => "red",
 Color::Green => "green",
 Color::Blue => "blue",
 }
}

get_color(Color::Red); // red

enum AnotherEnum {}

get_color(AnotherEnum); // Error: AnotherEnum is not a Color
```