Language
FAQ
What is µLang v1?
µLang v1 is the open contract layer of µLang: the contract style that ulang-lite implements and that this site publishes.
Is it used in production?
Yes. µLang Git evaluates its governed actions against twelve contracts with ulang-lite. The actions include claims, pushes, landings, tokens, workflow runs and tool calls, and all twelve contracts are on the examples page.
Why is there no NOT, arithmetic or function calls?
So that a decision is a bounded sequence of comparisons over facts the application supplies: deterministic, total, linear in the size of the contract, and easy to read in a review. The bounds scan refuses those constructs before parsing, so hostile input costs linear time. Patterns shows how to express the usual needs without them.
Can a contract read the time, a database or the network?
No. Everything a contract decides on is in the facts. That is what makes a recorded decision reproducible: the same contract and facts always give the same answer. See Time for passing time in as facts.
What happens with bad facts?
checkFacts rejects facts with a missing field, an extra field, or a value of the wrong type, and returns a message. decide assumes the facts have been checked. The command line and the example project's loadPolicy always check first.
Why must every clause have a source id?
Decisions name clauses, so the id is a stable public name. A log line that says ProductionDeploy.change_freeze should mean the same rule next year. Sources on constants say where a number comes from.
How do I change a contract safely?
Treat the digest as the contract's version:
- pin it in a test, so that every change is reviewed (Testing contracts);
- record it with each decision (Audit trail);
- pin the facts schema, so the service and the contract cannot drift apart (Pinning to a schema).
Is there a grammar?
Yes, in EBNF: see Grammar and Syntax.
Are there known bugs?
Two, both minor, listed with workarounds under errata.
Where do I report a problem?
On the µLang Git repository, which holds ulang-lite.
What license is ulang-lite under?
MIT, © 2026 Think Tech Holdings.