Having made full OpenGL games in C++, I can honestly say that this example is very, very good. One thing I don't understand is how input and output work with C

Having made full OpenGL games in C++, I can honestly say that this example is very, very good. One thing I don't understand is how input and output work with CHICKEN Scheme. With all the talk of monads on Hacker News lately, I was surprised that it wasn't discussed in the article. Does anyone have a link that discusses how CHICKEN Scheme calls imperative code from functional code? I found the wiki but there's a lot there.