bar.rb

# bar.rb
Facter.add("bar") do
   setcode do
       if (Facter.value("foo_1") == "option1") then
           "cond1"
       else
           "default"
       end
   end
end

foo.rb

# foo.rb
Facter.add("foo_1") do
   setcode do
       "option1"
   end
end