Re: Contextual::Return (was Re: could 'given' blocks have a return value?)
Damian Conway skribis 2006-08-31 9:08 (+1000): return want.rw ?? $lvalue :: want.count == 2 ?? (7,11) :: want.item ?? 42 :: want.list ?? 1..10 ::die Bad context; s:g/::/!!/ # :) Juerd -- http://convolution.nl/maak_juerd_blij.html http://convolution.nl/make_juerd_happy.html http://convolution.nl/gajigu_juerd_n.html
Contextual::Return (was Re: could 'given' blocks have a return value?)
In a message dated Tue, 29 Aug 2006, Mark Stosberg writes:
my $rm = sub { given $rm_param {
when Code { $rm_param(self) }
when Hash { %rm_paramrun_mode }
default{ self.query.param($rm_param) }
}}();
This is eerily like Contextual::Return, which made me wonder if it's even
required in Perl 6.
Obviously we can do
return do given want {
when :($) { ... }
...
};
But return do given want flows so badly, I desperately want some sugar
for this. Is there some and I missed it?
Trey
Re: could 'given' blocks have a return value?
Agent Zhang wrote:
According to S04, given {} is at statement level, so you can't use it
directly as an expression. But Perl 6 always allow you to say
my $foo = do given {...}
As well as
my $foo = do if foo {...} else {...}
I confirmed this both work now with pugs!
I think the 'do given' case is useful enough to document
more officially along with 'given'.
If you are thinking about the if/else case, ?? ... !! would be a
simpler way to write it.
Mark
could 'given' blocks have a return value?
Sometimes I use 'given' blocks to set a value. To save repeating myself
on the right hand side of the given block, I found I kept want to do this:
my $foo = given { }
...and have whatever value that was returned from when {} or default {}
populate $foo.
It turns out pugs already allow this, through the trick of wrapping the
given block in an anonymoose sub...which is then immediately executed:
my $rm = sub { given $rm_param {
when Code { $rm_param(self) }
when Hash { %rm_paramrun_mode }
default{ self.query.param($rm_param) }
}}();
Not only do you get implicit matching on the left side, you get implicit
return values on the right!
I'd just like to be able to clean that up a little to:
my $rm = given $rm_param {
when Code { $rm_param(self) }
when Hash { %rm_paramrun_mode }
default{ self.query.param($rm_param) }
};
Mark
Re: could 'given' blocks have a return value?
Mark Stosberg wrote:
Sometimes I use 'given' blocks to set a value. To save repeating myself
on the right hand side of the given block, I found I kept want to do this:
my $foo = given { }
...and have whatever value that was returned from when {} or default {}
populate $foo.
Isn't it still the case that the last expression evaluated within a
closure is returned by the closure? And isn't a given block just a
fancy kind of closure?
The question is whether or not a code block can be used where the
parser expects an expression; for instance, could one say:
my $foo = if condition {BAR} else {BAZ};
?
I'm no expert, but it occurs to me that allowing this could be a
parsing nightmare.
ISTR a programming construct along the lines of eval that is
effectively shorthand for sub { ... }().
It turns out pugs already allow this, through the trick of wrapping the
given block in an anonymoose sub...which is then immediately executed:
my $rm = sub { given $rm_param {
when Code { $rm_param(self) }
when Hash { %rm_paramrun_mode }
default{ self.query.param($rm_param) }
}}();
Not only do you get implicit matching on the left side, you get implicit
return values on the right!
I'd just like to be able to clean that up a little to:
my $rm = given $rm_param {
when Code { $rm_param(self) }
when Hash { %rm_paramrun_mode }
default{ self.query.param($rm_param) }
};
So what happens if you forget to include a default in the given?
--
Jonathan Dataweaver Lang
Re: could 'given' blocks have a return value?
On 8/30/06, Mark Stosberg [EMAIL PROTECTED] wrote:
Sometimes I use 'given' blocks to set a value. To save repeating myself
on the right hand side of the given block, I found I kept want to do this:
my $foo = given { }
According to S04, given {} is at statement level, so you can't use it
directly as an expression. But Perl 6 always allow you to say
my $foo = do given {...}
As well as
my $foo = do if foo {...} else {...}
my $rm = sub { given $rm_param {
when Code { $rm_param(self) }
when Hash { %rm_paramrun_mode }
default{ self.query.param($rm_param) }
}}();
Apparently ``do'' is a simplified version for this. :)
Cheers,
Agent
