Elamur Groupantsmlab-builtins-table-joins
The groupant beside mlab/src/builtins/table.rs in the Mova repository: what the code computes, what it never does, how to go back from its outputs, its invariants, cost and checks.
Facts
Implementation material. A Mova code model describes this code at one source revision: partial models, finite checks and their stated scope. It is not a reviewed general exposition, and its labels are shown as written, never raised.
Components
| component | label | where |
|---|---|---|
| approximant | partial | approximant |
| ast | partial | ../syntax.json |
| cost | symbolic source derived | invariant |
| descriptant | present | descriptant |
| invariant | partial | invariant |
| tests | partial bounded parent evidence | tests |
Obernants
The typed relations around the forward model: the behaviour complement (what the code never does), the reverse reconstruction (every input compatible with an output) and specialised views.
| id | type | label | where |
|---|---|---|---|
behavior_complement | behavior_complement | partial source derived model | behavior_complement |
reverse_reconstruction | reverse_reconstruction | partial source derived model | reverse_reconstruction |
multiplicity | multiplicity | partial source derived model | multiplicity |
failure_precedence | failure_precedence | partial source derived model | failure_precedence |
branch_relation | branch_relation | partial source derived model | branch_relation |
resource_cost | resource_cost | partial source derived model | resource_cost |
Model text
descriptant
mlab-builtins-table-joins
right_index stores nonmissing key rows in appearance order. innerjoin enumerates all matches then stable sorts by left keys. join rejects any duplicate right key before scanning left and requires every left row match. combine omits right keys, suffixes colliding names.
Epoch 2026-10-31: isolated source-bound fragment over bytes [18733,22422); includes no claim beyond this relation. Source hash f1b0959092cfcdd3cbd171a48d252ce4c1e652b1e56ed030c160e7667d8cbb54.
approximant
joins: forward relation
right_index stores nonmissing key rows in appearance order. innerjoin enumerates all matches then stable sorts by left keys. join rejects any duplicate right key before scanning left and requires every left row match. combine omits right keys, suffixes colliding names.
Domain: Well-shaped values and finite practical windows; effects delegated to it.fs. Physical filesystem not exercised.
Executable surrogate gap: no measured cheaper implementation with a useful scoped metric is supplied. Categorical/error/effect relations are exact obligations, not percent losses. Future numeric caps only1/2/5/10%.
invariant
joins: invariant and cost
innerjoin matches count sums left multiplicity*right multiplicity for each key; strict join enforces right<=1 globally.
Duplicate nonmissing right keys fail before first unmatched left; missing right rows never enter map.
Scope-specific cost: Expected O(nrk + nlk + m) hash match construction; innerjoin adds O(m log mk) stable ordering and O(mw) result materialization. Duplicates may make m=nl*nr.
models
behavior_complement
No NaN/None key matches. join excludes partial unmatched output and does not guarantee valid unique final names after suffix collisions.
reverse_reconstruction
Joined values admit multiple original unmatched rows and duplicate multiplicities; explicit source indices absent, so inverse is a relation. strict join admits right rows unused by left.
multiplicity
innerjoin matches count sums left multiplicity*right multiplicity for each key; strict join enforces right<=1 globally.
failure_precedence
Duplicate nonmissing right keys fail before first unmatched left; missing right rows never enter map.
branch_relation
right_index stores nonmissing key rows in appearance order. innerjoin enumerates all matches then stable sorts by left keys. join rejects any duplicate right key before scanning left and requires every left row match. combine omits right keys, suffixes colliding names.
resource_cost
Expected O(nrk + nlk + m) hash match construction; innerjoin adds O(m log mk) stable ordering and O(mw) result materialization. Duplicates may make m=nl*nr.
tests
Evidence boundary
See ../tests.md for the actual selected source test and mutant. These tests sample the file, not every fragment branch. No NaN/None key matches. join excludes partial unmatched output and does not guarantee valid unique final names after suffix collisions. Other branches here are source-derived and unexecuted unless the parent test explicitly calls them.
This page in Markdown → https://md.groupants.elamur.ai/free/en/mova/mlab/src/builtins/table.rs.groupant/joins.groupant/