Macro task 

macro_rules! task {
    ($name:ident: |$($field:ident: $field_type:ty$(,)*)*| $body:tt) => { ... };
    ($name:ident: move || $body:tt) => { ... };
    ($name:ident: |$cx: ident $(, $field:ident: $field_type:ty)*| $body:tt) => { ... };
    ($name:ident: move |$cx: ident| $body:tt) => { ... };
}