Improvements on the interpreter pattern

[danielo515]

Hello and again, thanks for this repo. I really liked the interpreter pattern. However, I want to know more, and it is hard to google. Do you have some specific links about blog post that I can read? If you have, probably will be nice to add them to the article. Also, it seems the syntax is outdated. It does not compile with any recent version of reasonml. Will you consider updating it?