> For the complete documentation index, see [llms.txt](https://robodex.gitbook.io/robodex-docs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://robodex.gitbook.io/robodex-docs/research/legacy-grammar-loop.md).

# Legacy Grammar Loop

The legacy loop lives in:

```
packages/research/agent_loops/grammar_loop.py
```

It is registered as:

```
grammar
```

## What it is

The legacy loop is a modular agent loop that builds and evaluates structural grammar rules. It predates the V2 `RobotDesignProgram` path.

## Modular loop API

The loop uses local primitives such as:

* `ModularAgentLoop`,
* `Node`,
* `add_edge`,
* `add_router`,
* node insertions.

These make the loop app-testable and configurable without requiring the product API to know its internal graph.

## Typical nodes

The loop can include nodes for:

* query normalization,
* state or checklist construction,
* structural rule generation,
* node-name resolution,
* structural rule compilation,
* evaluation,
* HITL summarization.

## LangGraph behavior

The loop can run without automatic LangGraph invocation unless the relevant environment flag enables it. This keeps unit tests from requiring every LangGraph runtime path.

## Difference from grammar V2

| Area                | Legacy `grammar`          | `grammar_v2`                                                 |
| ------------------- | ------------------------- | ------------------------------------------------------------ |
| Body representation | Structural rules          | `RobotDesignProgram` derivation                              |
| Compiler            | Grammar graph helpers     | `robot_program.py` compiler                                  |
| App path            | Still registered          | Current baseline is V2                                       |
| Determinism         | More agent-rule dependent | Deterministic expansion and lowering after program selection |

Use `grammar_v2` or `creative_qd_v2` for new product-facing generation unless there is a specific reason to test the legacy path.


---

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