So, all of this leads us to want to find a better way. We shouldn’t have to spend a lot of time writing a parser, and then spend an equal amount of time writing a printer, and then always remember that we need to synchronize future updates of one to the other. Ideally we should be able to write parser and printer code at exactly the same time, in the same package, guaranteeing that they will stay in sync.

And amazingly, it is possible. And even better, the theory of parser-printers looks remarkably similar to just plain parsers, so everything we have learned so far will be applicable. There are only a few twists and turns along the way that we have to be mindful of.

Let’s first develop the theory of printers much like we did for parsers. We will distill its essence into a single function, and we will explore examples of printers as well as operators on printers that allow us to build large, complex printers from smaller ones.