Closures in Ruby

Copy So, what's the final verdict on those 7 closure-like entities?          

                                                     "return" returns from closure
                                    True closure?    or declaring context...?         Arity check?
                                    ---------------  -----------------------------    -------------------
 1. block (called with yield)       N                declaring                        no
 2. block (&b => f(&b) => yield)    N                declaring                        no
 3. block (&b => b.call)            Y except return  declaring                        warn on too few
 4. Proc.new                        Y except return  declaring                        warn on too few
 5. proc                                    <<< alias for lambda in 1.8, Proc.new in 1.9 >>>
 6. lambda                          Y                closure                          yes, except arity 1
 7. method                          Y                closure                          yes

 The things within each of these groups are all semantically identical -- that is, they're different
 syntaxes for the same thing:
   
      1. block (called with yield)
      2. block (&b  =>  f(&b)  =>  yield)  
      -------
      3. block (&b  =>  b.call)
      4. Proc.new  
      5. proc in 1.9
      -------
      5. proc in 1.8
      6. lambda    
      -------
      7. method (may be identical to lambda with changes to arity checking in 1.9)

 Or at least, this is how I *think* it is, based on experiment. There's no authoritative answer other
 than testing the CRuby implementation, because there's no real spec -- so there may be other differences
 I haven't discovered.

 The final verdict: Ruby has four types of closures and near-closures, expressible in seven syntactic
 variants. Not pretty. But you sure sure do cool stuff with them! That's up next....