As for point 5, Arc uses certain characters as syntax abbreviations iff the special characters occur in what would otherwise be normal symbols (to the Scheme reader). So far, there's

  .a    ; is the same as (get a)
  a.b   ; is the same as (a b)
  !a    ; is the same as (get 'a)
  a!b   ; is the same as (a 'b)
  f&g   ; is the same as (andf f g)
  f:g   ; is the same as (compose f g)
  ~f    ; is the same as (complement f)

  ((get a) b)        ; is the same as (b a) by Arc's indexing
                     ; e.g., ("abc" 0) is #\a
  ((andf f g) x)     ; is the same as (and (f x) (g x))
  ((compose f g) x)  ; is the same as (f (g x))
  ((complement f) x) ; is the same as (no (f x))

There are precedence and associativity rules, such as

  a!b.c ; is the same as ((a 'b) c) because ! and . are 
        ; left-associative
  f:g:h ; is the same as (compose f g h)
  ~f:g  ; is the same as (compose (complement f) g)

  arc> (ssexpand 'a:b.c!d)
  (compose a b.c!d)
  arc> (ssexpand 'b.c!d)
  ((b c) (quote d))

  (catch
    (each x xs 
      (if (foo x) 
          (throw x))))

The last time I looked, ccc isn't used to capture and re-use first-class continuation objects except for this escape-clause purpose.

Here's a fine article on the subject - http://www.intertwingly.net/blog/2005/04/13/Continuations-fo...

1. you're inside atomic-invoke, call-w/stdout, call-w/stdin, or anything that creates context that needs to be undone on the way out. The problem is that a continuation from in here can be exited multiple times although it was entered only once.

2. similarly, you're inside protect, (equivalent to "finally" in java) - is the "after"-fn called, and if so, only once or for each re-entered continuation?

3. the continuation you jump into was originally running on another thread.

I should write tests to figure out what happens in all these cases, but if anybody knows the answers I can live with being lazy :)