Really? Sure, with warnings, you get a warning message. 
However, the program produces what it should produce, so the 
warnings generated are a nuisance. 

Perhaps you say "yeah, I know, but golly, perhaps in the 
future '@_[$a]' will mean something else". But that, I don't 
believe. In fact, in the future, in perl6, '@_[$a]' will be
the correct way and '$_[$a]' will be wrong way. I don't think 
anyone will give '@_[$a]' a meaning other than '$_[$a]' in 
perl 5.12, or another perl5 version. Ever.

(As for why this is all in 'code' tags, I've used [] several 
times in the posts. It's too much of a hassle to type 13
characters for each occurance)
[download]

Mostly, it's about saying what you mean. @_[$a] connotes a slice. $_[$a] connotes a scalar. The warnings aren't to tell you that the program won't generate what it's supposed to (although there are situations where the array context a slice provides could cause curious behavior), they're to tell you you're programming in a semi-literate way.

For what it's worth, I don't say "golly". Nor do I hide behind Anonymous Monk posts when I want to be snotty.

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Caution: Contents may have been coded under pressure.

... they're to tell you you're programming in a semi-literate way.

Nor do I hide behind Anonymous Monk posts when I want to be snotty.

Indeed. You're snotty while posting using the login name "Roy Johnson".