use 5.010;
use strict;
use warnings;

sub f { # ( [$:arg] )
    my $arg = do {$_ = shift // q{}; (length) ? $_ : 'default_value'};
    $arg;
    }

print f( )."\n";          # prints "default_value" 
print f( undef )."\n";    # prints "default_value" 
print f( q{} )."\n";      # prints "default_value" 
print f( 0 )."\n";        # prints "0" 
print f( 1 )."\n";        # prints "1" 
print f( 'value' )."\n";  # prints "value"