without measuring lengths or worring about that...
(use a #12 hook for the void map...)

map { $sum += $_ } @foo, @bar;
[download]

or if you're not fi^H^Hgolfing:

use strict;
my $sum = 0;
my @foo = ( 2,4,6,8 );
my @bar = ( 200,400,600,800 );
foreach (@foo,@bar) {
    $sum += $_;
}
[download]

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