From: Rudolf Polzer <denshimeiru-sapmctacher@...>
Date: 2003-08-08T02:06:32+09:00
Subject: Re: Why does Ruby have callcc?

Scripsit ille aut illa �Yukihiro Matsumoto� <matz@ruby-lang.org>:
> In message "Re: Why does Ruby have callcc?"
>     on 03/08/07, Mauricio Fern�ndez <batsman.geo@yahoo.com> writes:
> 
> |How consistent is this w/ your "no featuritis" policy?  In LL2 you had
> |to explain why Ruby had callcc but no macros; your answer was that the
> |latter are more easily abused ("too powerful" IIRC).
> 
> There's strong reason not to have macros in Ruby, as I believe.
> Continuation does not harm you very much.

Naq gurl'er gur bayl jnl gb trg bhg bs fbzr rivy pbafgehpgf...
see my other posting.

> |Do you still believe that or does "I provide the features, you use them"
> |represent a new policy?
> 
> I provide the features (which I choose), you use them.

And I wouldn't say featurities... continuations are ONE feature which
is a superset of coroutines, generators, setjmp/longjmp and the infamous
goto. And they're hard enough to use to prevent BASIC-like GOTO spaghetti
code.

- coroutines and generators are obviously NOT contained in the rest of Ruby.
- goto is a subset of setjmp/jongjmp and therefore not in Ruby (or is it?)

Well, you all know that goto can be done using case, well, at least something
similar:

def goto(n)
  $newlineno = n
end
def stop()
  $newlineno = nil
end

$lineno = 0
while $lineno do
  $newlineno = $lineno + 1
  case $lineno
    when                   100; puts "Hello World"
    when                   110; $i = 0
    when                   120; if $i > 10 then goto 160 end
    when                   130; puts "Current $i: %d" % [$i]
    when                   140; $i = $i + 1
    when                   150; goto 120
    when                   160; puts "Done!"
    when                   170; stop
  end
  $lineno = $newlineno
end

But that's no real goto, it's just case misuse. And possible even in
case-less languages like Perl using hashes or if...

BTW: I know it hurts to read such code. Be happy I didn't add "COME FROM".

-- 
PLEASE DO NOT GIVE UP