In early 2015, Uber Engineering migrated its business entities from integer identifiers to UUID identifiers as part of an initiative focused on using multiple active data centers. To do that, Uber engineers had to identify foreign key relationships between every table in the data warehouse—a nontrivial task by any accounting.

Uber’s solution was to observe and analyze incoming SQL queries to extract foreign key relationships, for which it built tool called Queryparser, which it open sourced.)

Queryparser is written in Haskell, a tool that the team wasn’t previously familiar with but has strong support for language parsing. To help each other get up to speed, engineers started a weekly reading group to discuss Haskell books and documentation.