While your points are definitely good advice, I'm not sure that's what he's asking about. I think the OP is asking about modifying the parameters to the subroutine in-place. For example: 
@a = (1..10);

sub x {
    foreach (@_) {
        $_++;
    }
}

x(@a);

print @a;  #prints 234567891011

[download]
So in principle, you can modify a subroutine's arguments using the default variable $_ inside a foreach loop. Question is, why isn't it working inside his recursive function?

In reply to Re^2: Modifying a parameter to a recursive function by bellaire
in thread Modifying a parameter to a recursive function by CoDeReBeL

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