Ratazong,
Never try to remove elements from the array you are currently looping through ... unless you are looking for trouble ;-) (or until you know exactly what you do!) This is probably the reason for your infinite loop.

Indeed. I think it would have been ok to go on and explain a couple of the situations where it is ok and how to address it:

for my $idx (reverse 0 .. $#array) {
    my $item = $array[$idx];
    if (some_test($item)) {
        splice(@array, $idx, 1); # remove the element
    }
}
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In the above case, it is ok to remove items because of the order they are being processed. Here is another example:

while (@work) {
    my $item = shift/pop @work;
    # Possibly push/unshift items onto @work
}
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In the above case we aren't looping over the array, we are using it as a boolean. When all the items have been removed the loop exists. This is useful when implementing your own stack/queue based solution and avoiding recursion.

I agree with your advice. I am just frustrated when people tell me don't do that unless you know what you are doing. I try to give them examples when it is ok, explain why or examples when it isn't ok and explain why not. I hope you don't mind that I took your advice a little further.