Code shared from the Rust Playground

playground.rs

macro_rules! commands {
    (
        ($cmd_enum:ident, $results_mod:ident, $ret_enum:ident),
        $(
            $cmd:ident -> $(
                $res:ident $(
                    ($($inner:ty),+)
                )?
            )|+
        ),+
        $(,)?
    ) => {
        commands!(@cmd_enum $cmd_enum {$($cmd),+});
        pub mod $results_mod {
            $(
                commands!(@res_enum $cmd $($res $(($($inner),+))?)|+);
            )+
        }
        commands!(@ret_enum $ret_enum $results_mod $($cmd),+);
    };
    
    (@cmd_enum $name:ident {$($cmd:ident),+}) => {
        pub enum $name {
            $($cmd),+
        }
    };
    
    (@res_enum $cmd:ident
        $(
            $res:ident $(
                ($($inner:ty),+)
            )?
        )|+
    ) => {
        pub enum $cmd {
            $(
                $res $(
                    ($($inner),+)
                )?
            ),+
        }
    };
    
    (@ret_enum $ret_enum:ident $results_mod:ident
        $($cmd:ident),+
    ) => {
        use $results_mod::*;
        pub enum $ret_enum {
            $(
               $cmd($cmd)
            ),+
        }
    }
}

commands! {
    (Command, results, CommandResult),
    Quit -> Ok,
    Init -> Ok | NeedCredentials | Fail(String),
    Fetch -> Ok | Fail(i32, String),
}

fn main() {
    let _ = Command::Quit;
    let _ = Command::Init;
    let _ = Command::Fetch;
    
    let _ = results::Quit::Ok;
    let _ = results::Init::Ok;
    let _ = results::Init::NeedCredentials;
    let _ = results::Init::Fail(String::from(""));
    let _ = results::Fetch::Ok;
    let _ = results::Fetch::Fail(1, String::from(""));
    
    let _ = CommandResult::Quit(results::Quit::Ok);
    let _ = CommandResult::Init(results::Init::Ok);
    let _ = CommandResult::Fetch(results::Fetch::Ok);
}