Today I want to write about something I've been working ages ago - specifically in March I wanted to see if I can extend a Java compiler to support LINQ´ expressions, too.

I probably spend more time on finding a good open-source compiler to experiment with than I later spent on trying things out, so let me share my preferred source with you: http://openjdk.java.net/ is a good address to start with.
More specifically http://openjdk.java.net/groups/compiler/ contains some valuable information about the way the compiler works.
A nice thing is that there is a branch that has added support for ANTLR which makes added language a tad bit easier since you get to change a grammar file instead of tweaking hand-written lexers and parsers. More info about it can be found at http://openjdk.java.net/projects/compiler-grammar/.
You can download the source code from http://hg.openjdk.java.net/ - don't follow the link to http://hg.openjdk.java.net/compiler-grammar/compiler-grammar, that one will only allow you to download part of the branch´.

I didn't come around to add support for LINQ in the end, but to get known to the compiler and the ANTLR grammer, I added support for the var keyword as known from C#, which allows for automatic type deduction and for anonymous objects (again using the C# syntax). Thus my changes allowed for the following to compile and execute correctly:

public class Test {
	public  static void main(String[] args) {
		// automatic type deduction
		var t = Math.atan(1);
		System.out.println( t );

		// anonymous type
		var i = new { Amount = 108, message = "hello" };
		System.out.println( i.Amount );
	}
}

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