Fighting spam with pure functions

Introduced FXL (Feature eXtraction Language), a domain-specific language optimized for spam fighting at Facebook. FXL is a subset of Standard ML designed for efficient data fetching across the graph. Its core innovation is the use of pure functions, which enables automatic optimizations like batching of data requests (leading to a ~20x speedup) and memoization of common expressions, significantly improving performance and enabling rapid adaptation to new spam threats.