Language Implementation Patterns

Pretty Printing Source Code

Building a pretty printer even for a specific language is surprisingly difficult. It’s even harder to build a general pretty printing engine. For an interesting research framework, take a look at the pretty printing language called BOX described by Merijn de Jonge in Pretty-Printing for Software Reengineering [De 02]. General pretty printers require some serious voodoo, and language-specific pretty printers tend to be messy ad hoc code blobs. Let’s see whether we can design a more formal language-specific pretty printer as a compromise.

We can make the problem dramatically easier if we relax it a little bit. Most pretty printers consider the right column a “do not exceed” hard limit. They must wrap everything before ...