Start with Nexa 3.0

Nexa 3.0 puts goals, implementations, and acceptance requirements in one program. Check a contract offline, build an artifact returning 42 inside OCI, then replay its lock. This guide uses released v3.0.0, pinned to source 2743796.

1. Install the pinned release

You need Python 3.10+, Git, and uv. Execution supports Linux/macOS: Docker Engine on Linux, or Docker Desktop / Colima on macOS.

git clone --branch v3.0.0 --depth 1 https://github.com/Nexa-Language/Nexa.git
cd Nexa
uv sync --locked --all-extras
uv run nexa --version

Confirm Nexa v3.0.0. Run the following commands from this directory. Standalone wheels are on the release page; the nexa-lang name on PyPI belongs to a different project.

2. Write a complete contract

Save this as answer.nx:

language "3.0"
program Answer {
    goal answer() -> Int {
        intent "Return 42"
        implementation value 42
    }
}

uv run nexa check answer.nx --json

check returns program IR, diagnostics, and open obligations; this example has no open obligations. This step needs no Docker, provider, or credentials and starts neither candidates nor models. language "3.0" selects Open Programs explicitly; existing programs retain the 2.4 compatibility entry point.

3. Build and replay

Start Docker and obtain the image pinned by the runtime example:

docker pull python@sha256:a0f57064cbdcd6285fa45f51237ab0b35ea8ebaed06a1f5973e89e19dfb86704
uv run nexa build answer.nx --environment examples/open_programs/offline.json --state .nexa/answer.db --json
uv run nexa build answer.nx --environment examples/open_programs/offline.json --state .nexa/answer.db --locked --json

The first build executes the literal implementation in real OCI. Its accepted answer result is 42, with passing typecheck evidence. Both builds use zero model calls; the second returns the same artifact digest. The default lock is answer.nx.lock. Preserve it with .nexa/answer.db, which stores the objects referenced by the lock. A missing image or unavailable Docker returns executor_unavailable.

4. Leave an implementation open

Goals and contracts introduces implementation open: a model proposes implementations within a budget, while deterministic checks and model reviews produce separate evidence. Read environment setup and budgets before explicitly requesting resolution. Repository writes follow the exact patch authorization workflow.

Continue with evidence, revision and recovery, developer tools, or 2.4 → 3.0 migration.

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Source and validation · open_language / open_execution