Macro create_node 

macro_rules! create_node {
    ( name: $name:expr,
      ( $( $in:ident : $it:ty ),* ) ->
      ( $( $out:ident : $ot:ty ),* ) $( $body:stmt )+ ) => { ... };
    ( $name:ident
      ( $( $in:ident : $it:ty ),* ) ->
      ( $( $out:ident : $ot:ty ),* ) $( $body:stmt )+ ) => { ... };
}

Macro to generate a Node (Task). It requires: a name (as used in the solver to execute it), a set of inputs, a set of outputs, and a set of statements which are the body of the task