The Haxl Project at Facebook [pdf]

Wait, Facebook uses Haskell? I had no idea. There is little information about the size of the codebase though. I could only dig up a talk from 2009 and a tool to modify a PHP codebase with abstract-syntax-tree transformers in Haskell [2]. Can somebody give some more insight on their internal use of the language?<p>Anyway I think it&#x27;s great that they have a hybrid codebase. With projects like HipHop and this Haskell backend it looks like they are gradually moving away from PHP as their main language.<p>[1]: <a href="http://cufp.galois.com/2009/abstracts.html#ChristopherPiroEugeneLetuchy" rel="nofollow">http:&#x2F;&#x2F;cufp.galois.com&#x2F;2009&#x2F;abstracts.html#ChristopherPiroEu...</a> [2]: <a href="https://github.com/facebook/lex-pass/tree/master" rel="nofollow">https:&#x2F;&#x2F;github.com&#x2F;facebook&#x2F;lex-pass&#x2F;tree&#x2F;master</a>

These are Simon Marlow&#x27;s slides from his ZuriHac 2013 talk about Facebook&#x27;s Haskell DSL for concurrent queries.

I&#x27;m sort of surprised that Facebook&#x27;s &quot;friends of&quot; is a directed graph, when the actual social graph is undirected. I guess they use enough directed edges for other things in that graph, but I&#x27;m sort of surprised their social graph isn&#x27;t undirected and ridiculously optimised as its own separate thing.

That&#x27;s extremely impressive. Datasources pluggable at runtime, no side-effect guarantee, hot-swapping code...

I believe Simon is also talking about this at the London Haskell Exchange at skillsmatter in October. I will definitely be attending this one!!

It&#x27;s a shame such cool technology is being put to use for something as trivial as Facebook.