writeonce/docs/08-project-structure.md

08 — Project structure: the writeonce monorepo

Canonical map of the repository: what every root directory is and who writes to it. Companion to CLAUDE.md (working rules), the status board (00-status.md), and the story arc (stories/language-runtime-database/00-story.md).

writeonce is one compiled language, one runtime, one embedded database, one binary: OCaml woc compiles .wo source to a .wob image, the C wovm runs it, and woc <dir> bakes the two into a single standalone executable. The prior Rust wo runtime was removed 2026-08-18 (see plan/discarded.md); the tree below is only the current project.

The one-page map

writeonce-all/
├── compiler/     OCaml `woc` — lexer→parser→types→owner→emit; produces the compiler binary
├── runtime/      C `wovm` — the register VM that runs .wob images (src/); phase A–F C reference (wo-rt.c, bench/)
├── database/     C embedded engine — class-shaped tables, secondary indexes, typed WAL + recovery
├── tests/        corpus/ — conformance fixtures: run / compile-fail / trap / gc
├── scripts/      oop-e2e.sh (corpus runner), mkdist.sh / install-accept.sh (packaging), sample acceptance
├── docs/         ALL documentation: numbered docs, stories/, plan/, examples/, superpowers/
├── .dev/         gitignored per-developer links + reference study trees (v1 crates, colibri, llama-cpp)
├── justfile      task runner: woc-/wovm-build, the *-test gates, oop-accept, dist, install-accept
├── VERSION       single-sourced toolchain version (stamped into woc/wovm; asserted by `just dist`)
└── README.md     the getting-started front door (also the writeonce.de landing content)

Root directories in detail

compiler/ — the OCaml woc compiler

compiler/
├── dune-project
├── README.md            orientation: pipeline map, build/test commands
├── plan/                compiler-track docs: architecture.md + the woc plans
├── src/                 one module per stage: diag, token, lexer, ast, parser,
│                        types, owner, emit, disasm, dump
├── bin/main.ml          the woc executable (check / --emit / build / version modes)
└── test/                golden runner + golden/ fixtures per stage

Doctrine: OCaml stdlib only — no Menhir, no ppx, no opam libraries; handwritten lexer and recursive-descent parser. Build: just woc-build; gate: just woc-test. Architecture map: plan/compiler/architecture.md.

runtime/ — the C wovm VM

The register interpreter that loads and runs .wob images, plus the arena, inferred GC, and the systems stdlib (fs/time/env/net/proc/json). runtime/src/main.c also reads an image embedded in its own binary (/proc/self/exe), which is how woc build produces a standalone executable. wo-rt.c + bench/ are the phase A–F io_uring event-loop reference that fed the design (see plan/exploration/c-runtime/00-plan.md).

Doctrine: C11, libc only, direct syscalls; computed-goto dispatch with -DWO_ISO_C fallback; ASan/UBSan gates. Build: just wovm-build; gate: just wovm-test (both dispatch flavors + cli_smoke).

database/ — the embedded engine

Statically linked into every wovm (and every test binary) — one binary, no separate database process. Class-shaped row slabs, an open-addressing id hash, secondary-index multimaps with @unique enforcement, foreign-key restrict, and a typed write-ahead log (len|crc|payload|mark, ack-after-fsync, torn-tail drop, boot replay). Every class is a table; durability is opt-in via WO_DATA. See database/src/CODE-LOGIC.md. The query surface that drives it lives in the compiler (emit.ml), lowered to engine builtins — no SQL text in the image.

tests/, scripts/

• tests/corpus/ — the conformance spine: run/, compile-fail/, trap/, gc/. Exact-outcome matching: byte-equal stdout, exact WO-E###, exact trap code. Driven by scripts/oop-e2e.sh (just oop-e2e).
• scripts/ — oop-e2e.sh (corpus), mkdist.sh + install-accept.sh (tarball packaging), and the per-sample acceptance scripts (employee-accept.sh, log-watcher-accept.sh).

docs/ — all documentation

docs/
├── 00-*, 01-problem.md, 08-*.md   status / principles / code-review / problem / structure
├── stories/                        the canonical iteration arc (language-runtime-database/)
├── examples/                       log-watcher/, employee/, employee-list/ samples
├── plan/                           compiler/ plans, oop-vm/ contracts, exploration/ studies,
│                                   discarded.md + learnings.md registers
└── superpowers/                    specs/ (approved designs) + plans/ (implementation plans)

Repo rule: documentation belongs here; code directories keep one orientation README each.

.dev/ — developer-local + reference

Gitignored per-machine tooling state plus reference/ study trees: the v1 wo-* crates workspace, colibri/llama-cpp vendored studies, and linux//go/ source symlinks. Read-only; nothing here is built by the main gates.

Build & test flow

just woc-build + just wovm-build produce the two binaries; just oop-accept runs the full milestone gate (compile-time budget, conformance corpus under ASan, single-binary smoke, both unit gates). Sample acceptance: just employee (database), just log-watcher (systems stdlib). Packaging: just dist → writeonce-<ver>-linux-amd64.tar.gz, proven by just install-accept.

Naming conventions

• Binaries: woc (OCaml compiler), wovm (C VM); a woc build / woc <dir> output is named by the project's wo.toml.
• Plan/spec files: YYYY-MM-DD-<topic>.md under docs/superpowers/{specs,plans}/; compiler plans under docs/plan/compiler/; normative contracts under docs/plan/oop-vm/.
• Sample projects live under docs/examples/<name>/ with their own wo.toml and module justfile.