From: Allison Randal
> Garrett Goebel wrote:
> >
> > Why does C<when>'s EXPR pay attention to the topicalizer
> > regardless of associated variable?
> >
> > Why introduce the special case?
....
>
> Why? Because it's oh-so dwim. Think about it, if you've just typed a
>
> given $x { ...
> or
> given $x -> $y { ...
>
> you know for a fact that you're going to want every C<when> to
> compare against the $_ or $y. Why force people to type:
>
> when $y =~ /a/ {...}
> when $y =~ /b/ {...}
> ...
>
> when you already know what they mean? And yes, it's the
> common case. How many times do you think you'll have a
> switch statement and want the case to compare against
> some value external to the switch?
Not just some value external to the switch, but the value in $_.
I now see the DWIM aspect. Thanks BTW.
But how often will people have non- C<when> statements within a C<given>
scope that'll need the special case handling so they can see a different $_
than C<when>?
To adapt your example:
$hi = 'hello';
$x = 'burt';
for $hi {
given $x -> $y {
when /burt/ { print "Go Away" };
default { print };
}
}
or without the special case:
$hi = 'hello';
$x = 'burt';
for $hi -> $y {
given {
when /burt/ { print "Go Away" };
default { print };
}
}
The second is obviously more explict, but does but requires a few more keys
be typed. I wonder if the C<given>/C<when> special case is really going to
be used regularly enough to justify the loss of clarity, consistency, and
the additional obfuscation potential.
$_ = 'foo';
given 'bar' -> $z {
if /foo/ { ... } # true, $_ = foo
when 'bar' { # true, $_ = bar
if /foo/ { ... }; # true, $_ = foo
}
$_ = 'baz'; # $_ = baz
when 'bud' { # false, $_ = bar
if /baz/ { ... }; # true, $_ = baz
}
}
I guess the next question in the context of the following is:
Larry Wall wrote in Apocalypse 4:
> It should be possible to make user-extensible syntax look
> just like built-in syntax.
How would I create a user-extensible construct that works like given/when?
I'm guessing the answer is: you don't.
