As the executive sponsor for this effort, I'd like to point out that we considered a wide variety of options. Java (and other JVM languages) as well as node.js,

As the executive sponsor for this effort, I'd like to point out that we considered a wide variety of options. Java (and other JVM languages) as well as node.js, ruby, python, C++, and others. We also already had in-house Erlang experience, but chose not to go with that for web services for various reasons. Haskell really is special, in that it represents a very strong point very far out on the "statically typed" spectrum. Among the options, it had the best bang for the buck. Erlang was also functional, but not statically typed. C++ was statically typed, but not functional. The others were largely not sufficiently better than our existing PHP solution, and/or were beat out by Haskell in the consideration. It's also important to understand that Haskell is not replacing PHP; it's augmenting PHP. We have many millions of lines of PHP running, serving many millions of active users, and there would be very little value in porting the "long tail" of that business logic. Meanwhile, there is huge value to be un-locked in gaining tight error checking and great performance on the "important core."