Less CSS - Expressions and Traps

In an average case, less expressions are easy to use, very useful and behave the same way as expressions in any other programming language. Unfortunately, their interactions with the rest of css syntax can occasionally cause somewhat quirky behavior. Adding to that, next less language version will change in backward incompatible way and expressions are affected too.

This post shows when and why quirky behavior happens, which problems are going to be solved by planned changes and which traps will still remain there.

Less CSS - Tips and Trics

Less is declarative language designed to behave and look as closely to css as possible. Less started as an attempt to make css style sheets easier to read and maintain and then added more features and abilities. It evolved so much that it became theoretically possible to do anything with it.

This post shows some less known but very useful less features. It also contains list of potentially useful workarounds and tricks you can use if the default less syntax is not sufficient for what you need. Finally, last chapter shows one practical application of those tricks. We will create mixin to auto generate vendor prefixes for css declarations.

ANTLR - Semantic Predicates

Parsing simple grammar with antlr is simple. All you have to do is to use regular expressions to describe your language and let antlr generate lexer and parser. Parsing big or complicated languages occasionally require more, because describing them in regular expressions only can be hard or even impossible.

Semantic predicates are java (or C++, or JavaScript, or ...) conditions written inside the grammar. Antlr uses them either to choose between multiple alternatives or as additional assertions to be checked. They can be placed inside both lexer and parser, but this post focus only on their usage within the parser. They add a lot of power to antlr.

Project Report - Less4j

Few months ago I decided to create java port of less.js. Less is an extension of CSS - it adds constants, mixins, ruleset nesting, namespaces and so on. Both reasons why I picked up less and short less introduction are written in introduction into less.

This report starts with current project status and its possible future directions. Second part recaps development and my experiences with used tools. Finally, the last part sums up why did I started with the project in the first place and whether it was worth it.

Travis-CI - Continuous Integration Server

Travis-CI is hosted continuous integration server for Github projects. The continuous integration part is fairly standard: it runs unit tests and report results after each project change.

The hosting part is unusual: the service runs tests on their own infrastructure and provides access to test results. The user does not need his own hardware nor to install and run the server. All that is part of the service.

Any public repository hosted on Github can use Travis-CI for free. Private repositories have to pay and the Travis Pro version they get is a bit different from the regular one.

This post is mainly about the free version. First chapter describes what Travis-CI does. Second part contains few things about Travis-CI server, infrastructure and organization behind it. Mini review with our experiences is located in the last chapter.

Tackling Comments in ANTLR Compiler

Most compilers treat comments as just another meaningless whitespaces. They identify them in the source code and then throw them away. On the other hand, things are a bit harder if you need to know comments content and their position.

Such requirement is not too common and official ANTLR documentation does not says much about how to do it. The compiler we have been working on needed to preserve comments, so we had to come up with our own solution. This post documents it.

First chapter introduces our compiler. It describes what it does, where it is located and how it is written. Second chapter explains our comment preserving requirements. The rest of the post describes datastructures and algorithms used in our solution.

Wro4j, Page Load Optimization and Less.js

Wro4j is primary a JavaScript and CSS merge and minimization library. Its original purpose was to speed up the page load. However, its final design made it easy to add integration with LESS, CoffeScript and few other technologies.

Less was introduced in previous article. In short, it is CSS with object oriented inheritance, variables and few other additional features. It is compiled into regular style sheets and served to the browser. Less was written in JavaScript and usually runs in the browser. If you want to run it on the server side, you have to use wro4j or some other integration library.

The post is mostly wro4j tutorial with focus on Less integration. It explains how wro4j works and how to configure it. There is very little about Less and almost everything is about wro4j.