From: Carlos <angus@...>
Date: 2004-03-10T20:28:34+09:00
Subject: Re: Why there is no Continuation.new ?

[gabriele renzi <surrender_it@rc1.vip.ukl.yahoo.com>, 2004-03-10 09.14 CET]
[...]
> Btw, I wonder what's wrong with a more rubyish way to use
> continuations.
> the sample from ri :
> 
>  arr = [ "Freddie", "Herbie", "Ron", "Max", "Ringo" ]
>  callcc{|$cc|}
>  puts(message = arr.shift)
>  $cc.call unless message =~ /Max/
> 
> To me this seem crying to become:
>  arr = [ "Freddie", "Herbie", "Ron", "Max", "Ringo" ]
>  cc= Continuation.new # optional &blk 
>  puts(message = arr.shift)
>  cc.call unless message =~ /Max/

Because callcc doesn't return a continuation, but, first: the value of
the block, and second: the argument to #call.

Here is an example (I am not good with examples...):

arr=[:a, :b, :c, :d]
message = callcc {|$cc| arr.shift}
#       ^-- this is the returning point
#           in the first invocation (callcc), it returns the value of the block
#           when we reach (2), it comes back here and returns :EOF
#           when we reach (3), it comes back here and returns the
#             argument to $cc.call() (arr.shift)
if message.nil?
        $cc.call(:EOF)     # (2)  if we reach the end of the array,
                           #    we go back and return this symbol instead
end     
puts message
$cc.call(arr.shift) unless message == :EOF    # (3) we go back until
                                              # we get an :EOF

Good luck.