grammar-inference-engine/SHOWCASE.md

# Dervish — Showcase

<p align="left"><img src="dervish-logo.png" alt="Dervish" width="180"></p>

Infer the **unwritten convention** from existing examples. Given N example
sequences, produce a ~100-char grammar that captures the structural
pattern — in far fewer tokens than the originals.

```
a.b       → a then b (concatenation)
(a+b)     → a or b (disjunction)
r?        → optional (zero or one)
r+        → one or more (iteration)
r+?       → zero or more
```

## 1. Ansible Galaxy roles (15 geerlingguy roles) — flagship

15 popular Ansible roles by Jeff Geerling. There is NO written convention
for the module ordering in `tasks/main.yml`. Our grammar is its first
explicit description:

```
Grammar: fail?.(include_vars+set_fact+package+file+template+service+...)+.
         include+?.(npm+pip)+?.lineinfile?
```

Every role: check preconditions → OS-specific vars → install packages →
configure with templates → start services → optionally handle language tooling.

All 15/15 match. **~29× compression** (7200+ modules → ~250 chars).

**Why it helps an LLM:** Generating a new Ansible role, the LLM knows the
exact structure: fail-check first, then vars, then packages, then config/svc.
No guessing.

## 2. Helm chart (kube-prometheus-stack, 6 configs)

6 different `values.yaml` files rendered through the same chart:

```
Best: iDRegEx | MDL 1433
Grammar: ServiceAccount.ClusterRole.ClusterRoleBinding.Service.Deployment
```

The **minimal core** every config must deploy. CRX captures the full
vocabulary (19 kinds). Which one an agent uses depends on the task:
- Bootstrapping a new cluster: iDRegEx — what you can't skip
- Writing a complete chart: CRX — everything you might need

## 3. GitHub Actions (cross-project Go lint, 6 jobs)

Lint jobs from prometheus, goreleaser, cosign, sigstore:

```
Best: CRX | MDL 13.6
Grammar: actions/checkout.(actions/setup-go+run:echo+run:sudo)+.
         golangci/golangci-lint-action?.megalinter?
```

Four independently-maintained Go projects converged on: checkout → setup Go → run golangci-lint. Only the biggest add megalinter.

**Why it helps an LLM:** Setting up CI for a Go project on GitHub Actions? The grammar encodes an emergent cross-project convention — four teams wrote the same pipeline without coordinating.

## What doesn't work

| Dataset | Problem |
|---------|---------|
| Dockerfiles | Too simple — just the Dockerfile spec |
| Pre-commit (cross-project) | 252 unique hooks, no common core |
| GHA per-project | One repo = too many job types |
| Prometheus rules | Schema-enforced, no convention |

Sweet spot: **multiple implementations of the same abstract task**
with a shared but undocumented pattern.

## Usage

```python
from bex.mcp_server import infer_best_grammar

output = infer_best_grammar(
    sequences=role_sequences,
    prefer="crx",
)
```