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Expression binding a variable a pattern also binds depends on plan order #596
Description
What happens
An expression binding ([(f …) ?x]) overwrites ?x at the point where optimizer::plan places it. When a pattern also binds ?x, the answer depends on whether that pattern runs before the expression or after it, so native (which reorders by selectivity) and --features wasm (which keeps source order) disagree:
(transact [[:a :age 30] [:b :age 40] [:p1 :score 41]])
(query [:find ?a ?x :where [?e :age ?a] [:p1 :score ?x] [(+ ?a 1) ?x]])- Native runs
[:p1 :score ?x]first, then the expression overwrites?x:[30 31] [40 41]. The score constraint is lost. - Wasm runs the expression first, then the pattern joins on it:
[40 41].
Both the executor and the streaming engine do this; the engine reproduces the executor (decision 2 of the #545 plan).
Rule (settled with the maintainer, 2026-10-14)
Every plan must return the same rows the same number of times; only the order of rows may differ, and only when the query sets none.
An expression whose output variable is bound by another clause unifies: it keeps the rows where its result equals the bound value (standard Datalog), wherever it runs. So [(+ ?v 1) ?v] never matches, and two expressions binding the same variable must agree. This is a breaking change for v3.0.0: queries that relied on overwriting change (CHANGELOG, Breaking changes). Equality follows the join rules (#545): floats by IEEE ==, and a keyword equals a ref to the entity it names.
Also
A test that runs the engine's query matrix with reordering on and off in one build, and requires the same rows, so plan-dependent answers fail CI. Related: #594 (pseudo-attributes), #546 (substituted floats in not bodies).
Activity
Merge pull request #598 from project-minigraf/docs/594-596-spec
Merge pull request #601 from project-minigraf/feat/596-unify
adityamukho commentedon Oct 15, 2026
Fixed on
v3by #601 (3a5fdac): an expression binding a variable another clause binds now unifies (keeps the rows where the values are join-equal), on the executor, evaluator and streaming engine; the first binder in:wheretext gives the value.tests/plan_independence_test.rschecks a query matrix with reordering on and off. Docs: project-minigraf/minigraf-docs#18. Ships in v3.0.0.