Macro step 

macro_rules! step {
    ($text:expr $(,)?) => { ... };
    (fg=$fg:expr, $text:expr $(,)?) => { ... };
    (bg=$bg:expr, fg=$fg:expr, $text:expr $(,)?) => { ... };
    (length=$length:expr, $text:expr $(,)?) => { ... };
    (bg=$bg:expr, fg=$fg:expr, length=$length:expr, $text:expr $(,)?) => { ... };
    (length=$length:expr, $text:expr, $( $arg:expr ),* $(,)? ) => { ... };
    () => { ... };
}

colorfully steps through code