Collect every matching person

Intent

I want to collect every matching person.

Correct formFrozen execution sceneBoundary

Wrong form and why it stays silent

Collect takes a comprehension, not a predicate call with an unbound variable.

Incorrect form

evaluate collect(eligible(p));

Correct form

Arxo Law

language "law.core" version "0.2";
package recipe.m02 version "1.0.0";
namespace "urn:recipe:m-queries:02";
entity Person;
relation registered(p: Person);
relation eligible(p: Person);
rule Admit strict { for p: Person; when registered(p); then eligible(p); }

Frozen execution scene

Input / variant	Question	Expectation
1. two persons	collect p: Person where eligible(p)	evaluation_status == COMPUTED;
2. empty domain	collect p: Person where eligible(p)	evaluation_status == COMPUTED;
3. contested membership	collect p: Person where eligible(p)	evaluation_status == COMPUTED;
4. rule removed	collect p: Person where eligible(p)	evaluation_status == COMPUTED;

two members collected

Arxo Law

test "two members collected" {
    given {
        context { legal_time @2026-09-13; decision_time @2026-09-13T09:00:00Z; knowledge_time @2026-09-13T09:00:00Z; timezone "UTC";  }
        assert registered(entity_ref("urn:recipe:m-queries:p")); assert registered(entity_ref("urn:recipe:m-queries:q"));
    }
    evaluate collect p: Person where eligible(p);
    expect evaluation_status == COMPUTED;
}

empty domain collects nothing

Arxo Law

test "empty domain collects nothing" {
    given {
        context { legal_time @2026-09-13; decision_time @2026-09-13T09:00:00Z; knowledge_time @2026-09-13T09:00:00Z; timezone "UTC";  }

    }
    evaluate collect p: Person where eligible(p);
    expect evaluation_status == COMPUTED;
}

disputed membership excluded

Arxo Law

test "disputed membership excluded" {
    given {
        context { legal_time @2026-09-13; decision_time @2026-09-13T09:00:00Z; knowledge_time @2026-09-13T09:00:00Z; timezone "UTC";  }
        assert registered(entity_ref("urn:recipe:m-queries:p")); assert not eligible(entity_ref("urn:recipe:m-queries:p"));
    }
    evaluate collect p: Person where eligible(p);
    expect evaluation_status == COMPUTED;
}

Removed from the program: rule Admit strict { for p: Person; when registered(p); then eligible(p); }.

removed rule collects nothing

Arxo Law

test "removed rule collects nothing" {
    given {
        context { legal_time @2026-09-13; decision_time @2026-09-13T09:00:00Z; knowledge_time @2026-09-13T09:00:00Z; timezone "UTC";  }
        assert registered(entity_ref("urn:recipe:m-queries:p"));
    }
    evaluate collect p: Person where eligible(p);
    expect evaluation_status == COMPUTED;
}

The composition of value is pinned by an extra check: scene 1 returns [p, q], the others — []. This is a set of a finite known domain, not a promise of completeness of all possible persons.

A separate negative JSON input is obtained from the scene 1 query by deleting comprehension.kind. The normative JSON schema rejects it, but both implementations answer COMPUTED and [p, q], with full byte parity. This is a reproducible defect of both implementations: structural input checking is incomplete. The correct query form remains mandatory; agreement of two answers does not legalize invalid JSON.

Check of result fields and extra inputs:

Python

>>> import runpy
>>> checks = runpy.run_path("docs/recipes/m-queries/resources/check.py")
>>> checks["collections"](https://github.com/arxohq/law/blob/master/docs/recipes/m-queries/2)
True

Counterfactual

The sidecar mutation reproduces LDC-E0201. Counterfactual table variants are executed separately; input errors are not passed off as NEITHER.

Boundary

An empty collection is a computed result. A corrupted query must yield QUERY_INVALID; the measured loophole is described above. An ordinary generator requires Established: Contradiction in scene 3 is excluded. Intentional inclusion of conflicting supports needs an explicit supported(P).

Pitfall

A wrong form or arity is not a divergence of derivation.