This is a fascinating project. Haxl is the brainchild of former Glasgow Haskell Compiler lead* Simon Marlow.<p>The tl;dr of Haxl: what if you could describe accessing a data store (a la SQL) and have the compiler and library work together to "figure out" the most efficient way to perform queries, including performing multiple queries in parallel? That's what Haxl does, it allows you to specify the "shape" of your query, the type checker verifies its correctness, and the library executes it in parallel for you, without the developer having to know about synchronizing access or anything.<p>Here's a link to their paper (PDF): <a href="http://www.haskell.org/wikiupload/c/cf/The_Haxl_Project_at_Facebook.pdf" rel="nofollow">http://www.haskell.org/wikiupload/c/cf/The_Haxl_Project_at_F...</a><p>* - I am not sure if he's still committing, or if he's only doing application development. His accomplishments in Haskell land though, are many.<p>Edited: I removed my comment about GitHub issues, seems it's a known problem. :)