Re: Sort of do it once feature request...
Michele Dondi [EMAIL PROTECTED] writes:
Every time I've desired a feature for Perl6 it has turned out that either it
was already planned to be there or I have been given good resons why it would
have been better not be there.
And you've done it again. What you ask for is already there. See below.
Now in Perl(5) {forum,newsgroup}s you can often see people doing stuff like
my @files=grep !/^\.{1,2}/, readdir $dir;
Letting aside the fact that in the 99% of times they're plainly reinventing
the
wheel of glob() a.k.a. File::Glob, there are indeed situations in which one
may
have stuff like
for (@foo) {
next if $_ eq 'boo';
# do something useful here
}
for @foo {
next if (($_ ne 'boo')..undef)
# do something useful
}
whereas they know in advance that Cif can succeed at most once (e.g. foo
could really be Ckeys %hash).
Or another case is this:
while () {
if (@buffer MAX) {
push @buffer, $_;
next;
}
# ...
shift @buffer;
push @buffer, $_;
}
while {
if 0..MAX { push @buffer, $_; next }
end
--
Piers Cawley [EMAIL PROTECTED]
http://www.bofh.org.uk/
Re: Sort of do it once feature request...
Piers Cawley skribis 2005-09-26 16:34 (+0100):
And you've done it again. What you ask for is already there. See below.
next if (($_ ne 'boo')..undef)
if 0..MAX { push @buffer, $_; next }
IIRC, flip flop will not return as the .. operator. Also, the global
state of syntactic flip flops makes me be afraid of using them in subs.
Juerd
--
http://convolution.nl/maak_juerd_blij.html
http://convolution.nl/make_juerd_happy.html
http://convolution.nl/gajigu_juerd_n.html
Re: Sort of do it once feature request...
On Mon, Sep 26, 2005 at 05:42:31PM +0200, Juerd wrote:
: Piers Cawley skribis 2005-09-26 16:34 (+0100):
: And you've done it again. What you ask for is already there. See below.
: next if (($_ ne 'boo')..undef)
: if 0..MAX { push @buffer, $_; next }
:
: IIRC, flip flop will not return as the .. operator.
That's correct, though we haven't decided what to call the flipflop
operator. Wants to be relatively long, huffmanly speaking, so
flipflop() could work. Could maybe be infix:thru or infix:till or
some such. Could have ^ forms as well. I'm not sure about preserving
the line number hack though.
: Also, the global
: state of syntactic flip flops makes me be afraid of using them in subs.
When you say that sort of thing nowadays, think state variables. So
if truify() till falsify() {...}
macroizes to something like:
if state $s ?? $s = falsify() !! $s = truify() {...}
Actually, I think that's the old ... operator. You'd write it slightly
differently to allow it to falsify immediately.
if state $s ?? $s = falsify() !! $s = truify() !falsify() {...}
Or something like that...
But yes, even with that desugaring, it does mean you're not writing
pure code in the functional sense.
Larry
Re: Sort of do it once feature request...
HaloO,
Larry Wall wrote:
... though we haven't decided what to call the flipflop operator.
Sorry, I'm totally out of scope to what 'the flipflop operator' is.
Could you be so kind to give some hints. Thanks in advance.
if state $s ?? $s = falsify() !! $s = truify() !falsify() {...}
Or something like that...
It is beautiful to see all these double-char boolean connectives at work
but again I'm hopelessly confused what you are referring to.
BTW, has dropping the '::' from the ternary alleviated its beeing a macro
and it has now a simple
infix:?? !!:(condition, true_block, false_block -- Bit) {...}
signature? The Bit there is actually oversimplified because it should be
the supertype of the two alternative blocks.
--
$TSa.greeting := HaloO; # mind the echo!
Re: Sort of do it once feature request...
TSa skribis 2005-09-26 19:39 (+0200): Sorry, I'm totally out of scope to what 'the flipflop operator' is. Could you be so kind to give some hints. Thanks in advance. http://perldoc.perl.org/perlop.html#Range-Operators Juerd -- http://convolution.nl/maak_juerd_blij.html http://convolution.nl/make_juerd_happy.html http://convolution.nl/gajigu_juerd_n.html
Re: Sort of do it once feature request...
HaloO, Juerd wrote: TSa skribis 2005-09-26 19:39 (+0200): Sorry, I'm totally out of scope to what 'the flipflop operator' is. Could you be so kind to give some hints. Thanks in advance. http://perldoc.perl.org/perlop.html#Range-Operators Thanks. I'm glad that 1..Inf these days is just a lazy closure or some such. Does someone consider this 'inner boolean state' and the 'magical auto-increment algorithm if the operands are strings' of the Perl5 range op a feature worth preserving? -- $TSa.greeting := HaloO; # mind the echo!
Re: Sort of do it once feature request...
TSa skribis 2005-09-26 20:32 (+0200): Does someone consider this 'inner boolean state' and the 'magical auto-increment algorithm if the operands are strings' of the Perl5 range op a feature worth preserving? Yes, many someones do. Juerd -- http://convolution.nl/maak_juerd_blij.html http://convolution.nl/make_juerd_happy.html http://convolution.nl/gajigu_juerd_n.html
Re: Sort of do it once feature request...
On Wed, 21 Sep 2005, Joshua Gatcomb wrote: I have mocked up an example of how you could do this in p5 with some ugly looking code: You may be interested to know that this has had an echo at http://www.perlmonks.org/index.pl?node_id=493826 mostly misunderstood in the replies, IMHO. Basically the idea is that not unexpectedly if you want a workaround TIMTWOWTDI already in Perl5. But what is conceptually interesting would be the possibility, In L~R's much better phrasing than mine, of modifying the optree or (P6's equivalent) as the code is running. The only ad-hoc solution given there that is really along these lines is Diotalevi's one at http://www.perlmonks.org/index.pl?node_id=493947 which -not completely undexpectedly either- made my head hurt... ;-) Michele -- Democracy is two wolves and a sheep deciding what to eat for lunch. Liberty is a well-armed sheep contesting the vote.
Re: Sort of do it once feature request...
On Wed, 21 Sep 2005, Joshua Gatcomb wrote: Cheers, Joshua Gatcomb a.k.a. Limbic~Region Oops... I hadn't noticed that you ARE L~R... Michele -- Your ideas about Cantorian set theory being awful suffer from the serious defect of having no mathematical content. - Torkel Franzen in sci.math, Re: Die Cantor Die
Re: Sort of do it once feature request...
Michele Dondi wrote: On Wed, 21 Sep 2005, Joshua Gatcomb wrote: Cheers, Joshua Gatcomb a.k.a. Limbic~Region Oops... I hadn't noticed that you ARE L~R... In the tradition of i18n, etc., I had assumed that L~R was shorthand for Luke Palmer. You may want to keep up the old tradition of defining your acronyms once. :) =Austin
Sort of do it once feature request...
Every time I've desired a feature for Perl6 it has turned out that either
it was already planned to be there or I have been given good resons why it
would have been better not be there.
Now in Perl(5) {forum,newsgroup}s you can often see people doing stuff
like
my @files=grep !/^\.{1,2}/, readdir $dir;
Letting aside the fact that in the 99% of times they're plainly
reinventing the wheel of glob() a.k.a. File::Glob, there are indeed
situations in which one may have stuff like
for (@foo) {
next if $_ eq 'boo';
# do something useful here
}
whereas they know in advance that Cif can succeed at most once (e.g. foo
could really be Ckeys %hash).
Or another case is this:
while () {
if (@buffer MAX) {
push @buffer, $_;
next;
}
# ...
shift @buffer;
push @buffer, $_;
}
in which one wouldn't like the Cif condition to be tested any more after
it first evaluated false. Now efficiency is seldom a real issue in all of
these situations, and in the rare cases in which it is one may adopt
alternative strategies, like prefilling @buffer (with apparent referal to
the previous example). In some cases one could need refactoring into subs
to avoid duplication of code, but then the original logic may have been
more clear intuitively to start with...
Whatever, I feel slightly uncomfortable psychologically with the idea of
something that will be tested even when it's not necessary. So now I
wonder if Perl6 is already expected to provide syntactical sugar enough to
do what I want: which something easy enough to type to make a portion of
code (behave like it) silently evaporate(ed) after a condition has been
verified for the first time (or, say, n times). I think this is similar
to the functionality of macros, but as I said, this should be -to be
really useful- only a moderate bunch of keystrokes away from the code that
doesn't employ it...
Michele
--
I just said it was my conjecture. That doesn't mean I think it's right. :-)
- Larry Wall in p6l, Subject: Re: What do use and require evaluate to?
Re: Sort of do it once feature request...
On 9/21/05, Michele Dondi [EMAIL PROTECTED] wrote:
Letting aside the fact that in the 99% of times they're plainly
reinventing the wheel of glob() a.k.a. File::Glob, there are indeed
situations in which one may have stuff like
for (@foo) {
next if $_ eq 'boo';
# do something useful here
}
I have mocked up an example of how you could do this in p5 with some ugly
looking code:
#!/usr/bin/perl
use strict;
use warnings;
do_something(5);
sub do_something {
my $target = shift;
my $block;
my $block2 = sub {
print No need to check $_ against $target anymore\n;
};
my $block1 = sub {
no warnings;
if ( $_ == $target ) {
print Skipping 5\n;
$block = $block2;
next LOOP;
}
else {
print $_ is not $target\n;
}
};
$block = $block1;
LOOP:
for ( 1 .. 9 ) {
$block-();
}
}
Once the condition has been met, the code dynamically changes to no longer
check for the condition. Keep in mind, you are paying the price of
dereferencing as well as ENTER/LEAVE on subs to get this performance
benefit.
I will be interested to see what the experts say on this. I have often
desired this in long tight running loops and found that the ways to achieve
it (as shown above) are worse then leaving the op in.
Michele
Cheers,
Joshua Gatcomb
a.k.a. Limbic~Region
