First: thanks for even trying it out!

Yeah, if you don't leave off the final semicolon, it doesn't return the last value. In that case you would have to use a normal "return" statement. It's definitely a bug, but I left it in there for some time because I thought it was weirdly interesting. I'm going to get rid of that bug though in the next version.

> Second, according to the rules for omitting parentheses

Ah, I'm doing a bad job with the tutorial then. Parentheses don't work like they do in C-like languages. It's more like Lisp in that regard. Your last statement prints "square"="Function" because you're not invoking the function but getting the function pointer. The correct way would be (again, somewhat Lisp-like):

    square = { n |
      n * n
    };
    println (square 5);

Again, this would also be the solution to your last example.

I should probably make a general syntax paragraph as part of the tutorial, especially for people coming from C-likes where invokation goes function(a) instead of (function a).

Edit: there's a section on the site now to explain this, I hope this will make it easier.