Vocabulary: pitfalls

Wrong forms, silent outcomes, LDC-E diagnostics, typical mistakes of formalizers and AI agents, and how to detect them. Items marked “confirmed by runs” were reproduced during this research on the installed engine.

OverviewBoundariesCorpus formsPitfalls

1. An individual name without declaration

registered_in(c, Astana) without const Astana — LDC-E1330: a bare name in term position must resolve to a const, an enumeration member, a package symbol, a dependency export, or a binder. Such a name is now a rejection at check. Detection: LDC-E1330 is fixed by declaring, not by renaming the fact: fact and rule must meet on one name.

2. A field in a constant’s label block

Arxo Law

const CAPITAL: Region = entity_ref("urn:...") { code: "KZ"; }

The block after a ready value holds labels; record-constructor fields are part of the value, not of the body. The AI agent carries over the “object with fields” habit from general languages — here the object is already complete to the right of =.

3. Keyword names and arity

const case: … — LDC-E0203 (event, case, calendar, action are hard keywords). On an entity the rejection is indirect: entity period; does not parse, and every use of the type turns red (LDC-E2101). A literal’s arity off-declaration (registered_in(c) on two parameters) is LDC-E2103. Detection: check every use against the declaration — names in Law DSL are not inferred but verified.

4. A constant type not matching

const BASE_FEE: Decimal = 10000 KZT — LDC-E2111. Percentage and money type spellings from prose are not resolved by the current compiler (LDC-E2101): write Decimal for 25 percent and Money for 10000 KZT. Confirmed by the research.vocabulary.company_registry teaching package: pub const MAX_RATE: Decimal = 25 percent; — check OK. The AI agent, having read prose type names, writes them directly — and gets a rejection: prose describes the intent, the compiler the 0.2 cut.

5. A subtype the wrong way round

Company in a Branch slot — LDC-E2104 (no implicit conversions). One direction only: a subtype fits its supertype, the reverse is a rejection. Confirmed by the research.vocabulary.subtype_key teaching package: registered_in(b, r) with b: Branch compiles because the slot is Company, not the reverse.

6. Members of different enumerations in one guard

l == first with l: RiskLevel — LDC-E2122: such a comparison answers with TYPE_ERROR, and it poisons the whole case document, so the spelling is rejected at check, not at runtime. Members have no order: < over members is TYPE_ERROR too. Detection: check every member guard against the guard parameter’s type, not against a “similar-looking name” of a neighbouring enumeration.

7. A constant through itself (statics silent)

const A: Decimal = A; — check is silent, runtime rejects with CYCLIC_CONSTANT on every case of the package. Detection: only by running law test; eye review — look for self-closure in const … = … chains.

8. Dotted spelling is the same member (former silent trap)

l == RiskLevel.high, l == high, and pkg::high are one constant reference. The dotted spelling used to travel into the compiled output as an identifier answered by no node, and the rule silently never fired — no diagnostics, no issue. Closed today; meeting an old package’s rule “that never fires” with a dotted member — check the build version, not the logic.

9. Repeated name; key over a foreign parameter

A repeated declaration in the package, including in another of its files, is a rejection LDC-E1201: a package’s namespace is one. key(z) with no z parameter in the signature is LDC-E1304. Detection: law engine check names the repeated name and the foreign parameter; fix — one declaration per name, keys only over signature parameters.

10. Out-of-slice form; undeclared predicate

member = "string" in an enumeration and import … as are out-of-slice 0.1 forms: LDC-E0206. A literal of a predicate never declared as a relation is LDC-E2102 (neighbour rejections: LDC-E2101 — unknown type, LDC-E2103 — foreign arity, LDC-E2104 — type mismatch, see items 3–6 above). Detection: check the literal against the relation declaration — there is nothing to write a rule about until the name is in the vocabulary.

11. Import without context; standard-library versions and names

A package with an import compiles only with a presented import context: without it every import and every qualified reference is rejected, while check stays green. An explicit prelude-package import at a different exact version is LDC-E1110; a reserved standard-library name on package is LDC-E1113; an unknown prelude package is LDC-E1114. A package declaration shadowing a prelude type is a warning, not an error. The header language version is checked against the registry exactly: "0.2.0" for "0.2" is LDC-E1401.