I'm actually getting fond of these single-point-of-entry for learning type of sites for a language. Along with the Prolog one that I saw here yesterday, I think they really make picking up a non-mainstream language a whole lot easier.

I remember when I was trying to start learning Common Lisp, I found it a little difficult for the lack of a resource similar to these. Eventually I stumbled upon PCL and LispBox and managed to take some baby steps. So kudos to the author.