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Postings from August 2013
On 28-Aug-13 16:20, Zefram via RT wrote:
> via RT wrote:
>> My proposal:
>> Since we can label any statement (now), why not have the reset operator take a label argument?
> I think the toggle operator is a wart that we should lean towards
> removing, not something to encourage wider use of. The context-dependent
> behaviour is particularly nasty to handle internally, compared to other
> context-dependent operators.
>
> If you like the toggle behaviour, I suggest that you should implement
> a cleaner version of it (certainly including explicit operations on
> named toggles) on CPAN.
>
> -zefram
>
>
Although it certainly isn't the most elegant of Perl's operators and
could have been done differently/better at the beginning of time, it
exists. It is used, and it's more than a wart - no matter how ugly the
internals. It provides a very concise way to deal with the common issue
of processing data within brackets. (e.g. certificate operations on PEM
files such as BEGIN X509 (CERTIFICATE/CRL...) / DATA / END X509)
The suggestion for a cleaner version in CPAN is interesting; although
exactly how to go about that without a heavy dependency on
version-specific Perl internals is not obvious. I suspect that it's
really too closely coupled to Perl internals (for which I don't claim
expertise) to take this approach and end up with syntax as clean as the
current operator.
One might imagine a toggle object as a middle ground -- e.g.
$toggle = Toggle::new( '...', sub {/^--a$/} , sub {/^--b$/}); #
booleans have to be a coderef for short-circuit semantics
.......
sub use_function{
$toggle->reset if ($. <= 1);
while (<>) {
$out .= $_ if $toggle->test > 1;
}
}
- which could be made to work, but is hardly concise or as clear as the
existing syntax, especially when one considers that the object approach
also has scoping/initialization issues that the existing operator
hides. $toggle would have to be some file scope variable, so it would
often end up far from the point of use. And if the boolean inputs are
more interesting (e.g. /^--$a$/, where $a is a MY variable in the
use_function scope) things go downhill rapidly.
Note also that the range (a.k.a toggle) operator can not be overloaded.
(http://perldoc.perl.org/overload.html#BUGS-AND-PITFALLS final bullet),
so we can't use it for precedence or syntactic sugar.
And so we end up with my original suggestion as the least inelegant
solution: provide a mechanism for reseting the existing operator, such as
reset ['label']; or reset( ['label'], 2 );
Or any other syntax that expresses the semantics but is easier to deal
with in the internals.
--
This communication may not represent my employer's views,
if any, on the matters discussed.
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