RE: The Block Returns

[Austin Hastings]

> -----Original Message-----
> From: Luke Palmer [mailto:[EMAIL PROTECTED]
> Sent: Thursday, October 02, 2003 10:23 PM
> To: Jeff Clites
> Cc: [EMAIL PROTECTED]; [EMAIL PROTECTED]
> Subject: Re: The Block Returns
> 
> 
> Jeff Clites writes:
> > >Speaking to the practical side, I have written code that has to 
> > >disentangle
> > >itself from the failure of a complex startup sequence. I'd love to be 
> > >able
> > >to build a dynamic exit sequence. (In fact, being able to do <C>&block 
> > >.=
> > >{ more_stuff(); };</C> is way up on my list...)
> > 
> > I've wanted to do that sort of thing before, but it seems simpler 
> > (conceptually and practically) to build up an array of cleanup 
> > subs/blocks to execute in sequence, rather than to have a .= for 
> > blocks. (Another reason it's handy to keep them separate is in cases in 
> > which each needs to return some information--maybe a status which 
> > determines whether to proceed, etc.)
> 
> But this is already supported, in its most powerful form:
> 
>     wrap &block: { call; other_stuff() }

Hmm, no.

That does a call, which presumes a return, which burns up who-knows-how-many mips. 
Given that the compiler is being forced to remember the code in case someone overloads 
the semicolon operator, or whatever, I don't think it's unreasonable to catenate the 
.source values of various blocks, and that seems a reasonable behavior for 
<C>infix:.=(Block, Block) {...}</C>.

Especially since the other way turns into:

  macro atexit(Block $b) {
    get_the_current_sub().eval("my &block = {};")
      unless defined &block;
    wrap &block: { call; $b(); };
  }

Which makes two calls per additional whosit.

Frankly, I think I'd rather see:

  macro atexit($code) is parsed(/{ <Perl6.line>* }/) {
    get_the_current_sub().eval("my $block;")
      unless defined $block;
    $block .= $code;
  }

  macro return($retval) {
    eval($block) if defined $block;
    leave Routine, $retval;
  }

But that imposes <C>eval()</C> pretty frequently. Better to provide some lower-level 
hackish way to agglutinate Blocks.

=Austin