Thanks, but may want to correct:

method_as_fun = o.my-method

which should be:

method_as_fun = o.my_method

and the examples themselves just look a little crazy, imo. Not crazy because of what you are trying to do, but in how you are trying to do it. What was the intent of calling a method that defines an argument without an argument? That's not a problem of the language; that's just an error in coding. There are all kinds of things in Ruby to handle method definition. Arguments can have defaults. You can use splat and unsplat to handle unspecified arguments and composing arguments of various # on the fly. You can pass in blocks specifically (&something) or optionally (yield, etc.). Procs allow argument sillyness and returning the parent method by explicit return in the proc body, lambdas don't, etc. Ruby is a great language, and you should give it a college try for several months to get the hang of it.

By the same token, I have no clue what you are trying to do here:

def f(x); def g(y); x + y; end; g(2); end; f(2) # undefined local variable or method `x'

You can define methods on object instances, if that is what you are getting at (define_method/class_eval/etc.), and getting familiar with blocks, procs/lambdas might help. It isn't JavaScript, but I can't think of that much that I couldn't do in Ruby (barring high performance, compile-time type checking, etc.)