InferNoLogic

Type checker for JsonLogic expressions with full type inference

Design goal

Infer the result types of JsonLogic expressions and possibly of data referenced in {"var": ...} expressions.

• without the need of extra annotations; full inference without extra JsonLogic syntax
• fast; should run in a browser while editing
• soundness over completeness; prefer false negatives over false positives. For example: in {"if": [predicate-expression, then-expression, else-expression]} require then- and else-expressions of the same type, even though JsonLogic allows them to differing ones.
• actionable error messages; No "Computer says no" but a location in the expression tree with as narrow a scope as possible, with some helpful humane hint. (Aim for Elm and Rust compiler helpfulness)

Usage

Install with npm or yarn:

npm install --save-dev @open-formulieren/infernologic
yarn add -D @open-formulieren/infernologic

References

Builds on implementations from domdomegg/hindley-milner-typescript-minimal for

• Algorithm W

  Damas, L. and Milner, R. (1982). Principal type-schemes for functional programs. Proceedings of the 9th ACM SIGPLAN-SIGACT Symposium on Principles of Programming Languages - POPL '82. https://doi.org/10.1145/582153.582176

• Algorithm M

  Lee, O. and Yi, K. (1998). Proofs about a folklore let-polymorphic type inference algorithm. ACM Transactions on Programming Languages and Systems, 20(4), 707-723. https://doi.org/10.1145/291891.291892