Simple iteration

Suppose we wanted to find everything we know about Alice. To do this, try:

engine.each("Alice", :_, :_) do |elem|
  puts "Alice's #{elem.predicate} is #{elem.object}"
end

#each takes a pattern and iterates over all known facts matching that pattern. :_ here is a wildcard that matches anything.

In a similar fashion, #select returns an array of all matching facts, and #find returns the first matching one.