Fighting spam with Haskell

This post details the migration of Facebook's Sigma spam detection system from an in-house FXL language to Haskell. Key technical contributions include the development of the Haxl framework to enable automatic batching and concurrent execution of data fetches, and the implementation of hot-swapping of compiled Haskell code for rapid deployment in a running production system. The post also discusses performance improvements achieved with Haskell over FXL, including a 20-30% increase in overall throughput, and optimizations made to the GHC compiler and heap management for multicore machines. It also highlights the use of Haskell's Foreign Function Interface (FFI) to integrate with existing C++ infrastructure.