Parsing textual input with IncQuery

Parsing textual notation has a long history in computer science. This long time has produced many great and efficient parsing algorithms, which were optimized to the extreme by compilers for different programming languages. However in the recent years the development of integrated development environments are accelerated, adding more and more services to previously simple features like code editors and automatic background compilation. These with the rise of domain specific language frameworks which allows the user to define an arbitrary language declaratively causes that present-day computers still struggle under the resource requirements of these technologies.

While waiting in front of a textual editor, I’ve started thinking about why does the editor need to re-run the parsing algorithm every time I hit button (of course I’m aware of the fact that the main cause of the slow responsibility is probably not the parsing algorithm itself). A fully incremental approach could make these tools more responsive which would remove a lot of pain from its users. As I’m already familiar with an incremental query engine (IncQuery) the thought about using it to parse text couldn’t leave my mind.

The following article presents the experiment I’ve done as a proof-of-concept. It’s far from being useful and reveals more problems than it solves it does not produce an AST just accepts or rejects the input string, however it may be interesting as an approach and maybe in the future it will be more than just a stupid idea. Continue reading “Parsing textual input with IncQuery”

Yet another textual modeling framework

Most of the time I try to avoid reinventing the wheel. And most of the time I fail and forced to do so. That’s what happened to me when I decided to write my own textual modeling framework. I’ve used (and currently using) Xtext in several projects and tried EMFText once. Both of them are great projects with great possibilities, but I’ve come across a problem which required a different approach. I needed a more dynamic toolkit, where the language is extensible and easier to maintain. Continue reading “Yet another textual modeling framework”

Review of Instant MuseScore

Since I’ve always been interested in computer-aided music notation and a strong proponent of open-source software, I’ve been advocating MuseScore among my fellow musician colleagues since multiple releases. When learning the usage of a new piece of software, questions always pop up about the most common sheet music engraving tasks. When Packt Publishing asked me to review Instant MuseScore, I was eager to see whether this e-book fulfills its promise of being a pragmatic hands-on quickstart guide to the first steps of using MuseScore. Here are some of my thoughts.

Its workflow-oriented structure is very practical (although I would definitely not put the “Barlines and repeats” section into the “Formatting” chapter, especially repeats are clearly not a matter of formatting). The tip about setting the velocity of special notes (e.g. slashes) was new and useful for me. The notes about potential caveats are also helpful and can save a lot of frustration.

For an “Instant” book which aims to be quickly skimmable, more formatting emphases would be good, as well as indicating the keyboard shortcuts for every command mentioned. The used version of MuseScore could be more prominent because there are major UI changes between new versions.

I would note that ties can be inserted with the numeric plus sign (on most keyboards this character is bound to Shift+3, which is reserved for inserting a third below), and also I think it would be important to emphasize that unfortunately, extracted parts are separate copies, not views (as opposed to MuseScore’s commercial counterparts).

When describing expression anchors, I miss mentioning that they also affect playback obviously, not just the layout of the sheet music. In the lyrics chapter, it would be also worth showing the keyboard shortcut of inserting a space into a syllable. (Though this is not the most common case, it occurs quite frequently in some languages, e.g. in Italian.)

One tiny but apparent technical issue with the PDF version of the e-book: the embedded font does not support the Cmd and the spacer icon.

Although I doubt that a book (especially a printed one) is the most suitable medium for teaching the usage of such a complex application (screencasts are better, the best would be tutorials integrated into the interface of the application itself), if you can afford its not too low price, Instant MuseScore will give you a gentle introduction to this feature-packed but yet maturing program.

Xtext Reflective Editor updated for Kepler

Today a new Eclipse version codenamed Kepler was released, with a lot of nice new features, including conflict handling during update, an update user interface for the Marketplace client or various EGit updates (my favorite is the Commit and Push button in the Commit dialog).

About the less visible stuff, in the modeling projects we use, e.g. EMF, Graphiti or Xtext also got some internal updates, resulting in the need to update our projects. As of now, I updated the Xtext Reflective Editor, as a change in EMF 2.9 made it unusable in Kepler.

I often use this tool to debug the Xtext-based parsers that use Xbase and model inferrers, as it displays the generated model using the EMF reflective editors. Version 0.5.5 is a recommended minor update – it works on both newer EMF/Xtext versions, but maintains compatibility with older EMF versions. It is still downloadable from our update site http://eclipse.cubussapiens.hu.

Thanks for all contributors the new, nice features of Kepler (and of course fixes as well). This can become a new platform for new projects for me – the reflective editor update is only the first of them.

Language Features Enhancing Trust

Alex just facepalmed.

if ( Boolean.TRUE.equals(employee.isHappy) ) {

“Wow, the human invention never ceases to come up with new ways to adorn boolean expressions! Too bad Eclipse doesn’t have a Quick Assist for simplifying them…”
Ah, one of those WWTC moments. That’s when the Show Annotation feature of Subversive comes in handy… which revealed that Bob is the author (unless he only adjusted the whitespaces in that line). “But he already left the office for today. Now, I’ll just simplify it and similar occurrences manually and tomorrow, I’m going to considerately mention to him that he could have written this condition umm… more concisely.” Alex pondered a bit over the commit message, but practiced self-restraint and wrote simply

Simplify boolean expressions...

(though he couldn’t help omitting those ellipses).
Next day, some of the tests of Bob’s module were failing.
– Hi Bob, could we have a look at your code? First, there are some red tests, and…
– Hmm, but I haven’t modified that module since yesterday. Let’s see the exception!
– Okay…

Exception in thread "main" java.lang.NullPointerException
at EmployeeLoader.loadEmployee(EmployeeLoader.java:41)

“Hmm, exactly the line I modified. But…” – thought Alex.
– …how could a simple condition without a single dereferencing cause a NPE?! – asked Bob, confused just like Alex.
– Uh-oh, I think I have a suspicion… Please show the declaration of isHappy

private Boolean isHappy;

Alex facepalmed once again, but this time the cause was himself.
– NOOO! The dreaded autoboxing! But again, why isn’t it a primitive boolean?
– Hey, now I remember! Employees are parsed from XML using an autogenerated schema. The attribute isHappy is optional, so it might very well be null.
– Sorry, Bob. I feel silly for acting without asking you in advance or running the tests before committing. See, I couldn’t have imagined how this kind of change could break.
– Take it easy, Alex. :) Now you can. In fact, I thought Boolean.TRUE would refer to the attribute’s type being non-primitive unambigously, and the Yoda condition would evoke the possibility of the null value immediately.
– I understand you, but to avoid such misunderstandings in the future, would you mind writing

if ( (employee.isHappy == null) && employee.isHappy ) {

to make it totally explicit that isHappy can be null? Or rather set an optional false value for this attribute in the schema?
– OK, I’ll consider.
Fortunately, Bob took the incident very lightly and his commit message was just:

Revert Alex's "simplifications" :)

The first thing Alex did was to set a warning for boxing and unboxing among the Java compiler settings. As he was accepting the changes, he thought: “Null and primitive types as well are billion dollar mistakes coming from arbitrary language design decisions which reflect implementation details. But at least they tought me to trust my fellow’s code – or at least to inspect the types before refactoring.”