Let’s consider the multiline comment in Java (and C/C++/C#, among others) which, you surely know, looks like this: /* * Comment text. */ This is an interesting construct. Paradoxically, it is extremely simple — I mean to describe in natural, human language (English or whatever) — but shockingly difficult to express in CongoCC. Or, that …
The poster child for this feature would be something like the C-style multiline comment, i.e. /** * comment */ It is actually surprisingly difficult to specify this in legacy JavaCC (or JavaCC21/Congo up until very recently). One way is to break it into multiple regexp patterns using the MORE feature. Or, alternatively, there is actually …
The following essay outlines the main evolution in the API generated by CongoCC from its origins in the Dark Ages up until now. The Journey of a Thousand Leagues Begins with a Single Step Let’s say you go on an excursion to a national park and there is a well known hiking trail that goes …
Some days ago, I added a new setting. If, at the top of your grammar, you write: TERMINATING_STRING=”some string”; this means that the input you’re parsing is guaranteed to end with that string. If the file ends with that string already, then it does nothing. Otherwise, it tacks that string to the end. In actual …
The TERMINATING_STRING setting, a new (and quite minor!) feature Read More »
There is now a syntax converter to convert legacy JavaCC (and some things in JavaCC 21) to the approved CongoCC syntax. You can execute it as: java -jar javacc-full.jar convert filename That will spit it out to stdout. More likely you want something more like: java -jar javacc-full.jar convert filename > outputfilename The converter converts …
The main goal of the JavaCC 21 project, soon to be renamed as CongoCC, is to develop a very capable, practical, usable parser generator tool. However, there is another overarching goal — perhaps not so much a goal, as a philosophy. That can be summed up in a single word: Demystification You see, somehow or …
NFA stands for “Nondeterministic finite automaton”. (Does that make you nervous?) Read More »
(The TLDR: Nested lookahead was always broken in legacy JavaCC. This is finally fully addressed (as of 11/26/2022) in JavaCC 21. However, since this fix has a lot of potential to break existing code, for now, the fix is only in effect if you put LEGACY_GLITCHY_LOOKAHEAD=false at the top of your grammar(s). Meanwhile, you should …
There is a scene that repeats itself in various James Bond films, usually towards the end. The archvillain has captured Bond. However, instead of just killing him, he has to do it in some very creative, slow manner, using some sort of Rube Goldberg contraption. Meanwhile, he tells Bond gleefully what his plans are for …
I shall tell you my plans but then I shall have to kill you, Mr. Bond Van Bruggen Read More »
A very annoying detail in computing (annoying in particular because the whole thing seems so utterly pointless) is this whole issue of line endings in text files. In Microsoft Windows, the operating system that dominates the desktop, a line ending is denoted by "carriage return" followed by "line feed", or CR-LF for short. (Namely the …
♫ I can still hear you saying ♫ ♫ You would never break the chain ♫ ♫ Never break the chain… ♫ Fleetwood Mac What we see frequently with JavaCC is cases where the original authors were actually quite perceptive: they anticipated certain problems and put in some dispositions to deal with them, but unfortunately, …