Macro node_trace 

macro_rules! node_trace {
    ($this:ident, $($fmt:expr),+) => { ... };
}

Conditional debug printing. (pure)

Usage: node_trace!(self, "debugging at step {}", self.__clock); (statement) Assumption: self has a field __trace: bool.

If the trace is enabled by means of self.__trace, pass all the remaining arguments to println! for debugging.