One of the very interesting lessons from Crenshaw's "Let's build a compiler" is that writing a simple, recursive descending parser isn't hard at all.
His _Compiler Construction_ book is short, sweet, and has a free PDF online (http://www.inf.ethz.ch/personal/wirth/books/CompilerConstruc...). Uses Oberon.
So writing it isn't all that hard. But changing it after you've written it is a recipe for disaster. I did that a couple of times and looked for A Better Way.
A tool like ANTLR, OTOH, makes re-purposing (and initial development and testing) easy, but at the expense of runtime performance.
Perhaps the lesson is, "write a few RDPs to get the hang of it and then make life easy on yourself"?
Law: You can't check code you can't parse. Checking code deeply requires understanding the code's semantics. The most basic requirement is that you parse it. Parsing is considered a solved problem. Unfortunately, this view is naïve, rooted in the widely believed myth that programming languages exist.