As you say, it is not equivalent. To do that you need some extra checks at the top of the 'loop' ie

  last unless /^\d+$/ and $_ <= 10;
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It is almost certainly a silly way to do it in Perl anyway. It is even a rather suboptimal way to do it in C.....

for(i=0;i<var;i++) printf( "%c", 97+i ); /* C or perl */

print map chr,97..96+$var;
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I don't mean the extra checks. I mean it doesn't preserve the semantics. Imagine if the OP's code didn't have the conditions in a strictly monotonic increasing or decreasing sequence, but in some completely random order. You couldn't emulate that simply by fiddling the conditions a little — you'd have to build a construct that's actually equivalent.

Makeshifts last the longest.