C-family syntax, UB-free semantics, ARC strings, sum types and pattern matching.

Welcome to the Dea programming language!

Dea is a systems programming language built through a staged bootstrap chain: each language level is compiled by the previous one, self-hosts, and then becomes the compiler base for the next level.

The design is conservative by choice: a small, precisely specified language whose semantics leave no room for undefined behavior. Operations are either well-defined or rejected - at compile time or with a named runtime error.

Tertium non datur.

This repository is a monorepo hosting the Dea language family. Each level is a self-contained subtree:

Dea/L0 is a small, UB-free systems language, compiling to C99, sufficient to host its own compiler. It is self-hosted through its Stage 2 compiler and is the canonical user-facing toolchain today. Start at l0/README.md for the L0 overview, quickstart, and language tour.

Dea/L1 carries post-L0 language growth: wider fixed-width integer types, float/double with an explicit floating-point contract, bitwise operators, top-level const, function pointer types, the unsafe function marker, fixed-size arrays, export manifests, and selective/aliased imports, among others. It currently exists as a bootstrap compiler implemented in L0 (stage1_l0) and consumes the L0 Stage 2 compiler as its upstream toolchain; it is not yet a release-bearing product. Start at l1/README.md and l1/docs/roadmap.md.

Dea is highly experimental, and the language itself is evolving daily. Dea/L0 is quite stable as of its 1.0.0 release, but no level is immune from breaking changes; when breaking changes land, they are properly incorporated into that level's semantic versioning.

At any given moment:

• the bleeding edge of Dea is the highest language level at its latest commit (today: Dea/L1 on the development branch);
• the stable version of Dea is the highest released level/version (today: Dea/L0 1.0.0).

When Dea one day becomes production-ready, or at least reasonably stable, it will be announced. Until then, consider Dea in constant evolution, even though its shape is progressively emerging.

Versions are scoped to one language level, not to the project as a whole:

• l0-v1.0.0 is a release of Dea/L0. There is no "Dea 1.0"; a project-wide version number is intentionally not defined.
• Release tags are level-prefixed: l0-vX.Y.Z and l0-snapshot-* are active today; l1-v* and l1-snapshot-* are reserved but not yet active.
• Pre-monorepo bare tags such as v0.9.0 and v0.9.1 remain valid historical references to early L0 development.

The full release-tag and release-line gating policy lives in MONOREPO.md.

Each Dea level implements its compiler in two stages: Stage 1 is written in an external host language (Python for L0, L0 itself for L1) and is the behavioral oracle; Stage 2 is written in the level's own language and, once mature, becomes the primary delivery vehicle. Level 0 is self-hosted today and is the compiler base used to build L1; L1 will subsequently self-host, and the process repeats for successive levels.

The architectural rationale is recorded in docs/decisions/, starting with docs/decisions/0001-two-stage-architecture.md.

The practical entry point today is Dea/L0. From a fresh clone:

make venv   # create the shared repo-local virtual environment
cd l0       # all L0 build/test/install workflows run from here

Then follow the install and quickstart instructions in l0/README.md. For Windows-specific setup, see l0/README-WINDOWS.md.

For L1 bootstrap development:

make venv
cd l0 && make use-dev-stage2   # prepare the upstream L0 compiler
cd ../l1 && make build-stage1

See l1/README.md for the current L1 workflow.

Monorepo structure, the root maintenance Makefile, the shared uv workspace, and the release-tag policy are documented in MONOREPO.md. The Dea-wide status snapshot lives at docs/project-status.md.

See CONTRIBUTING.md for developer workflow, setup, and validation commands, and SECURITY.md for the security policy.

MIT or Apache 2.0, at your option.

Third-party notices: THIRD_PARTY_NOTICES.

@googlielmo a.k.a. gwz