Everything is an expression in Ruby, yes. Even `class` and `def` and `module`, for example. Though class, as a specific example, returns nil, so it's not terribly useful that it is one.

In Lisp, "def..." macros, like defclass, defun, etc. return the symbol to which is bound the definition. Not essential, but useful at times. I tend to find Lisp is full of details like this.

Well, Common Lisp!

In the Scheme language, many imperative forms have an unspecified result. For instance, see R7RS 4.1.6: "the result of the set! expression is unspecified".

Also, a related misfeature is that function arguments can be evaluated in any order.

Yes, this is one of the things that I really want to punch the SSC for. Assignment should have a useful return value: even C, so often said to do The Wrong Thing, got that right.

But for those of you who aren't scheme programmers, it gets worse: because when RnRS says that the result of something is "unspecified" many implementations take it literally. That's right: in many Schemes, `set!` returns the literal value #<unspecified>. I swear I'm not making this up. It's awful.

To quote Jonathan Gabriel of Penny Arcade: "Baby, why you always gotta make me hit you?"

Yes, sorry, Common was implied (not claiming it should always be, but here I wrote it without thinking about others). Scheme's unspecified results are annoying indeed.