>This is the common rebuttal of PHP jokes - but pointing to a sole outlier is rarely a solid defense.

Sole outlier? Hardly. Half of the web is powered by PHP, including tons of websites with huge traffic and usage.

>Especially when they have created Hack[1] and HHVM[2]. So it's not entirely accurate to say they "use PHP."

Hack and HHVM do not show some inherent PHP issue that something like Ruby or Python would not have.

Hack is mostly an attempt to add type checking/hinting to PHP. The lack of type checking would be the same if they used Python or Ruby or Node+JS or whatever.

And HHVM is an attempt at a speedup, to work at Facebook like economies of scale. Considering that plain PHP is on par speedwise with Ruby and Python, that's again not something that would be saved using those other languages. Which is why Google tried to do Unladded Swallow (for Python), Dropbox does their own thing, RoR companies invest hard on speeding up Ruby/Rails, etc.

TL;DR: Hack and HHVM may be proofs of some lack in PHP for Facebook uses, but are not proofs of PHP lacking things compared to other similar languages like Python and Ruby.