I couldn't resist writing a "golfed" Perl 6 version, heavily inspired by functional programming techniques:

sub compress(*@a) {
    flat @a Zxx 1, (@a Zne @a[1..*-1])
}

say compress(<a a a a b c c a a d e e e e>).perl;
[download]

The *-1 is a workaround for a rakudo bug, in a perfect Perl 6 implementation 1..* would work too.