The Haxl Project at Facebook [pdf]

The Haxl Project at Facebook [pdf](github.com)

71 points by shangaslammi 12 years ago | 27 comments

omn1 12 years ago |

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?

Anyway I think it'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.

[1]: http://cufp.galois.com/2009/abstracts.html#ChristopherPiroEu... [2]: https://github.com/facebook/lex-pass/tree/master

Ixiaus 12 years ago | |

Yeah, they also bought out MailRank to get O'Sullivan.

mightybyte 12 years ago | | |

Yeah, but that wasn't for Haskell.

asdasf 12 years ago | |

Facebook hasn't been a PHP shop in a long time. PHP is only used on the front end site. New projects that come along are written in whatever language makes sense. Like facebook chat being in erlang for example.

enigmo 12 years ago | | |

I heard a rumor a while back that Facebook Chat was rewritten in C++... but I can't seem to find anything to verify that. Do you know if it's still Erlang?

shangaslammi 12 years ago |

These are Simon Marlow's slides from his ZuriHac 2013 talk about Facebook's Haskell DSL for concurrent queries.

mcintyre1994 12 years ago |

I'm sort of surprised that Facebook's "friends of" 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'm sort of surprised their social graph isn't undirected and ridiculously optimised as its own separate thing.

Scaevolus 12 years ago | |

An undirected graph is equivalent to a directed graph with doubled edges.

The only efficient way to implement an undirected graph is as a directed graph with doubled edges.

You want to list friends of Alice. Directed: query all friend(Alice, X). Undirected: query all friend(Alice, X) OR friend(X, Alice). Finding all friend(X, Alice) will be very slow without an index of all friend relationships with Alice in the second position. Storing this is harder than just storing friend(Alice, X) and friend(X, Alice).

mcintyre1994 12 years ago | | |

Oh of course, I see what you mean, thanks for the explanation.

seiji 12 years ago | |

For surveillance it's of great importance to know the difference between me being friends with Iranian nuclear scientists, them being friends with me, or us having mutual hugs going on.

mercurial 12 years ago |

That's extremely impressive. Datasources pluggable at runtime, no side-effect guarantee, hot-swapping code...

tel 12 years ago | |

The hot-swapping is very new and experimental, but if facebook has a need then Simon Marlow definitely has the capability bring that back to GHC core. He's already stated at least some of the hot swapping will make it.

boothead 12 years ago |

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

AznHisoka 12 years ago |

It's a shame such cool technology is being put to use for something as trivial as Facebook.

tel 12 years ago | |

There's a lot of critique that could be leveraged against Facebook, but I don't understand how you could call it trivial.

freyrs3 12 years ago | |

Simon Marlow said on reddit this morning that some of the technology is getting merged upstream into GHC 7.8. So we'll all benefit from it.

freehunter 12 years ago | |

Is there any reason it can't be used elsewhere? You could repurpose the solution into your own project and do something less trivial.