---
title: "mlab-interp-index-assignment — Mova code model"
description: "Mova code model of mlab/src/interp.rs: components with their labels, obernants and the model text."
url: "https://groupants.elamur.ai/free/en/mova/mlab/src/interp.rs.groupant/index-assignment.groupant/"
---
Elamur: [Mova](https://md.mova.elamur.ai/free/en/) · [Dictionary](https://md.dictionary.elamur.ai/free/en/) · [Research](https://md.research.elamur.ai/free/en/) · **Groupants**

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# mlab-interp-index-assignment

The groupant beside mlab/src/interp.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

- **kind:** groupant_fragment
- **status:** partial source bound model
- **source:** [`mlab/src/interp.rs`](https://github.com/ElamurAI/mova-free/blob/main/mlab/src/interp.rs)
- **source SHA-256:** `5c4d879d116b5fa0…`
- **covers:** Assignment and index-context evaluation boundary. (bytes 17664–19980)
- **part of:** [mlab-interp](https://md.groupants.elamur.ai/free/en/mova/mlab/src/interp.rs.groupant/)
- **repository folder:** [`mlab/src/interp.rs.groupant/index-assignment.groupant`](https://github.com/ElamurAI/mova-free/tree/main/mlab/src/interp.rs.groupant/index-assignment.groupant)
- **repository commit:** `855da7bd4a7b`

> **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](#approximant) |
| **ast** | partial | `../syntax.json` |
| **cost** | symbolic source derived | [invariant](#invariant) |
| **descriptant** | present | [descriptant](#descriptant) |
| **invariant** | partial | [invariant](#invariant) |
| **tests** | executed bounded checks | [tests](#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](#behavior-complement) |
| `reverse_reconstruction` | reverse_reconstruction | partial source derived model | [reverse_reconstruction](#reverse-reconstruction) |
| `rhs_precedence` | rhs_precedence | partial source derived model | [rhs_precedence](#rhs-precedence) |
| `missing_target` | missing_target | partial source derived model | [missing_target](#missing-target) |
| `end_context` | end_context | partial source derived model | [end_context](#end-context) |
| `column_coordinates` | column_coordinates | partial source derived model | [column_coordinates](#column-coordinates) |

## Model text


### descriptant

#### mlab-interp-index-assignment

Assignment and index-context evaluation boundary.

##### Epoch 2026-10-31

Half-open source bytes [17664,19980); bound by parent source hash and scoped byte hash. Model covers only this fragment; parent composition explains joins.

### approximant

#### Scoped forward relation

RHS Mat -> existing target Mat or undefined -> evaluate index args with pushed EndCtx -> index::assign -> store.

##### Domain and gap

Source-generated states within resource limits. Categorical relation has no executable percent surrogate.

### invariant

#### Scoped invariant

A function-handle RHS is rejected before an invalid index is evaluated.

##### Cost

Index expression evaluation plus index::assign costs and target growth/copy. EndCtx stack adds one entry per active index evaluation; dimensions use unchecked products.

### models

## Scoped typed relations

### behavior_complement

Nonmatrix RHS excludes target/index evaluation; failed undefined-target assignment excludes inserting that target. End-context evaluation must not retain its temporary stack entry after a returned error.

### reverse_reconstruction

Successful target matrix admits initial empty or existing matrices and many index/value histories; error text constrains first rejected stage only.

### rhs_precedence

A function-handle RHS is rejected before an invalid index is evaluated.

### missing_target

Undefined target uses dimensions 0,0 and is inserted only after successful assignment.

### end_context

Each index evaluation pushes then pops its dimension context before propagating its Result.

### column_coordinates

Indices delegate to index module, not direct Rust offsets.


### tests

#### Evidence scope

Parent selected tests: wave30_parse_runtime_and_output_state, wave30_bounded_state_and_fallback, parse_error_runs_nothing. This fragment shares parent syntax and finite checks; no separate test count or complete fragment coverage claim. Assertion-control association and unexecuted paths are in parent tests.md and source-test-map.json.