Macro pipeline 

macro_rules! pipeline {
    () => { ... };
    (
        $v: vis pipeline $i: ident {
            $($lit: ident $s: ty),*
            $(,)?
        }
    ) => { ... };
}

Declares pipelines. Pipelines are used to guarantee that communication is correct at compile-time.

pipeline! {
    pub pipeline MyPipeline {
        send String,
        receive String,
    }
}