Arrows to Arrows, Categories to Queries :: Reasonably Polymorphic

Sandy Maguire released catlang, an experimental programming language that compiles to a single PostgreSQL SELECT statement, on October 14, 2025. The hobby project, built during time off from work, uses an intermediate language grounded in abstract category theory—including arrow notation, functors, and distributive laws—rather than a conventional query syntax. Maguire demonstrated the language with a `count` function that computes a value via a loop-like construct desugared into categorical combinators such as `cochoice`, `dist`, and `▽`. The work matters as a testbed for applying category-theoretic semantics to real compilation targets, showing that arrow-based intermediate representations can be lowered to SQL. What to watch next is whether Maguire documents the arrow desugarer and expands catlang beyond its current proof-of-concept scope.