Macro graph 

macro_rules! graph {
    (
        nodes: ($($nodes:expr),*),
        connections: {
            $(
                $left_node:ident $( : $output:ident )? => {
                    $(
                        $right_node:ident $( : $input:ident )?
                    ),* $(,)?
                }
            )*
        }
    ) => { ... };
}

Syntax sugar for building a graph