Hmm. It occurs to me that if the goal's to do it in a single statement, it can be done quite easily:

#!/usr/bin/perl
use strict;
use warnings;

my @k = qw( a b c a b a );

my %i = do { my %h; map { $_ => ++$h{$_} } @k };

print join " ", %i;
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That's cheating of course, but so is tie. :-)

Makeshifts last the longest.