And you'll find that these code reviews are described "Review..." in the episode guide, e.g. "Review the AST printing
One way you could do it is by getting the gist of the code from the review and then working through the implementation yourself. That way you will have the high-level decisions made for you – e.g. now print the abstract syntax tree – and may get a feel for the techniques you use effectively and the mistakes you make – both of which will surely differ from Per's – and so put yourself in a decent position to develop as a programmer.