[mindstab]

That's not really saying anything. Facebook picked PHP in 2004 and is now stuck with it. They have a huge code base in it.

But there are a lot of indications they are moving away from it in all places they can. They still use it for front end work, but even there they have been one of the biggest innovators coming out with the HipHop PHP compiler.

Behind that they also came up with the Thrift RPC framework specifically so that the rest of their code and logic could be written in many other languages including Java, Python and Erlang.

Facebook is a lot more than PHP and they've pushed PHP innovation a lot too. I find their use of PHP as no clear indication PHP is the right or wrong choice. It's just the choice they made 7 years ago and are living with

[simonw]

http://www.quora.com/Why-hasn-t-Facebook-migrated-away-from-... has some insider insight.

[alexatkeplar]

Facebook have also built a Haskell tool to generate/update their PHP now as well, https://github.com/facebook/lex-pass