Avoiding Signature Avoidance in ML Modules with Zippers

Watch this 21-minute conference talk from POPL 2025 where researchers Clément Blaudeau, Didier Rémy, and Gabriel Radanne present ZipML, a novel path-based type system for ML-module language that solves the signature avoidance problem. Learn how floating fields function as zippers on signatures, allowing delayed resolution of signature avoidance issues while remaining invisible to users. Discover the four rules for simplifying floating fields without losing type-sharing, and understand how ZipML implements early and lazy strengthening along with lazy inlining of definitions to prevent signature duplication in the typechecker. The presentation covers the correctness proof through elaboration into M𝜔 and explains how this approach could be retrofitted into existing OCaml implementations.