Re: run-once code

[Dan Brook]

On Tue, 13 Jan 2004 20:37:21 -0800
David Storrs [EMAIL PROTECTED] wrote:

 Given this code:
  
 if ( some_expensive_lookup_function() = $MAX_RECORDS ) {
mark_that_we_have_reached_max_records();   
return;
 } 
 
 After I enter that block once, I never want to evaluate the condition
 again--I want the code to completely disappear from the bytecode (or,
 at least, be jumped around).  How would I do that in Perl 6?

Another approach would be to just memoize the subroutine. Thanks to the
spiffy new subroutine signature syntax it's absurdly easy e.g

  sub some_expensive_lookup_function() is cached { ... }

That's side-stepping the implications of memoizing a subroutine of
course, but it does save maintaining state in user-level code.

Dan

Re: Aliasing an array slice

[Dan Brook]

On 5 Jul 2003, Luke Palmer wrote:

  return [EMAIL PROTECTED] $begin .. $end ];

 I fear that this might take a reference to each element in the slice,
 rather than a reference to the slice

Yes, that would indeed return a list of refs in perl5. Can it also be
assumed that the magic hyper-operation of \() in perl5 will translated to
perl6, or (hopefully) will this behaviour become more explicit with
something like ^\() (is the carat still the hyper-operator character
btw?) ?

 Actually, you can't reference a slice!  Where the heck does the
 reference point?

Maybe this is a poor simile since references aren't pointers, but I would
imagine if references to slices were to exist they'd be something *like*
a pointer to a specific index in an array in C e.g

  #include stdio.h
  int main(void) {
char *str = a list of characters;
char *p   = str[2];
puts(p);

return 0;
  }

  __output__

  list of characters

Of course this isn't directly orthogonal to a reference of an array slice
but hopefully it illustrates my point. Or perhaps this could all just be
simply implemented with a tie() or some other such magic. Just thinking
out loud here :)

Dan Brook

Aliasing an array slice

[Dan Brook]

Will it be possible (or sane even) to bind a variable to an array slice
e.g

  ## correct syntax?
  my @array =  a list of values ;

  my @array_slice := @array[ 1 .. @array.end ];

Or would this merely bind @array_slice to the list returned by the slice,
or would it DTRT (in my eyes at least) and bind it to that particular
slice of @array?

Dan Brook

Re: Disappearing code

[Dan Brook]

On Thu, 09 Jan 2003 19:55:20 -0500
John Siracusa [EMAIL PROTECTED] wrote:

 Has there been any discussion of how to create code in Perl 6 that's
 there under some conditions, but not there under others?  I'm thinking
 of the spiritual equivalent of #ifdef, only Perlish.

If the perl6 command-line options are anything like perl5 then you
can just use the -P switch if preprocessor commands are your thing.

 In Perl 5, there were many attempts to use such a feature for
 debugging and assertions.

There has also been a proposal for patching perl5 to add assertions
which was recently discussed[1] on p5p, which if accepted has
implications for assertions in perl6 surely.

Dan

[1]
http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2002-11/msg00325.html