I know. I've seen it. Can you point to some unreadable code? Preferably one that does not fall into the 'operator overload ing abuse' category?

Go look up the sources for the Scala 2.8.0 compiler.

Worst and most difficult to understand code I have ever seen. It is simultaneously confusing, hard, badly commented and uses every single Scala feature I have ever seen, including non-root imports in the middle of files, extensions of anonymous classes sometimes with other anonymous classes, and my least favourite: path depended typing (sometimes from non-root imports started in one of several traits that may or may not have circular inherietence patterns).

But that said, it has never been a problem outside the compiler.

That's pretty interesting, because I had no trouble reading and understanding the sources of the compiler and writing simple patches for it ... and I'm not really a compiler guy and not a type theorist.

The Scala compiler is in my opinion one of the nicest code bases I've seen, considering the low-level stuff happening there.

I've never read or written a single line of Scala code, I was just trying to be helpful by providing a link where there's lots of Scala code..