sub yahoo()
{
    return "Easy";
}

print "${\yahoo()} does it!\n";
[download]

Oh, you asked for it!

Mark-Jason Dominus presented this at the Perl Conference. It's a generic way to evaluate a Perl expression inside a double-quoted string:

package Eval;

sub import
{
    my ($package, $name) = @_;
    $name = 'Eval' unless defined $name;
    my %magical_hash;
    tie %magical_hash =>Eval;
    my $caller = caller;
    
    *{caller . '::' . $name} = \%magical_hash;
}

sub TIEHASH
{
    my $self = \'fake';
    bless $self => Eval;
}

sub FETCH 
{
    my ($self, $value) = @_;
    $value;
}
[download]

Looks pretty freaky, eh? Okay, now try this:

use Eval => ':';

$salary = 43_000;
print "After your raise, you will make $:{$salary*1.06}.\n";
[download]

Yeek. Have fun!

Thanks for the example, CMonster, but I don't get it to work on my machine (ActiveState 5.005_03).

I get:

Warning: Use of "caller" without parens is ambiguous at C:\... line 11. syntax error at C:\... line 29, near "use Eval =>"

So I change from:

use Eval => :;

to:

use Eval ( ':');

at line 29.

Then I get:

Modification of a read-only value attempted at Eval.pm line 17

and that one I just don't know what to do about. I tried to change

my $self = \'fake'

to:

my $self = {}

at line 16, but that didn't help.

/jeorgen

I had to make the following changes:
• Add a $ to the typeglob line: *{$caller . '::' . $name} = \%magical_hash;
• Do a two-step reference creation in TIEHASH():

  my $self = 'fake';
  $self = \$self;
  [download]

• Use a more standard use statement: use Eval (':');
It won't run under strict, though, with the symbolic reference in the import() bit.