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.

Perl 6 - second systems done right

In reply to Re: reduce like iterators by moritz
in thread reduce like iterators by LanX

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