Trait Watcher 

pub trait Watcher: Send + Sync {
    // Required method
    fn saw(&self, fact: &Fact);
}

Told what happened, as it happens.

Required Methods

fn saw(&self, fact: &Fact)

One fact. Whatever this does, it does not fail: there is no useful answer to “the log could not be written” in the middle of a run, and a Result here would make every emit site a decision about somebody else’s storage.

Implementors