With the mention of the parser's performance, I am reminded of Rich Kilmer's 2004 RubyConf presentation. Rich used Ruby to test reliability of a distributed system with hundreds of Java VMs. Some of the serialized data was stored as XML (over 1M lines!), which was slow to parse and load. Rich modified the program to serialize the data as Ruby code, which loaded much faster (https://www.infoq.com/news/2007/06/infoq-interview-rich-kilm...):

> Chad Fowler and I over basically 2 weeks, took the Java Debug Wire Protocol specification [...] turned it into a DSL in Ruby, and used that DSL to generate the packets for sending and receiving data. So we used the DSL in Ruby as a generator to generate Ruby code, as the whole protocol and then I used that at Darpa. They were trying to say “we could freeze the agent society from within the agent society will send messages, and it took about 7-8 minutes for all the messages to propagate and everything to freeze and then go quiet. I had a Ruby process that was running all 300 VM’s were underneath it, and I could freeze it in about a half of second. All 300 of them! And you actually could watch the CPU use because we had a monitor and the CPU use has dropped to zero. And it freaked them out. And what was great was you could turn it back on, and all the agents came back on. But time had been lost. And it was like alien abduction lost time, ten minutes went away, “what happened to us?” It was a bizarre thing because they were agents and they were planning on things and all of sudden 10 minutes just went away. But it was interesting to show how Ruby could actually be used as this kind of harnesses to wrap around things like systems.