Effect V4

Effect v4

The Bun and Node Effect targets share one Effect HTTP router and run on the exact Effect v4 beta recorded in versions.json. Ground claims in the checked-in implementation and pinned upstream source, not in remembered v3 APIs.

Authority order

1. Treat the benchmark contract in README.md and the compiling files under src/ as the local behavior source of truth.
2. Verify package APIs against installed typings and repos/effect at its pinned release commit.
3. Use repos/effect/migration/ to translate v3 code. Use web documentation only when the exact-beta source does not answer the question.

Keep repos/effect read-only. Never edit it or import runtime code from it.

Read next

• Read references/core-patterns.md for generators, services, layers, typed errors, Promise boundaries, and high-value v3-to-v4 translations.
• Read references/http-server.md before changing the router, requests, responses, Bun/Node adapters, server layers, or runtime launch.
• Read references/upgrade-workflow.md before changing an Effect beta pin or advancing the source-oracle submodule.

Workflow

1. Read the affected benchmark source and its matching reference above.

2. Search the exact source oracle before using an unfamiliar or unstable API:

   rg -n -- '<symbol>' repos/effect/packages
   

3. Preserve route parity between Bun and Node by changing shared behavior in src/effect-router.ts; keep runtime-specific wiring in src/bun/effect.ts and src/node/effect.ts.

4. Preserve the benchmark semantics in README.md, including dynamic path/query extraction, JSON parse-and-serialize behavior, streamed file responses, shared background routes, and disabled server logging.

5. Keep changes narrow. Do not add production-oriented middleware, tracing, or abstractions that distort benchmark startup, memory, bundle size, or throughput.

Non-negotiables

• Pin effect, @effect/platform-bun, and @effect/platform-node to the same exact beta. Do not use ^, ~, or the floating beta dist-tag.
• Import v4 HTTP APIs from effect/unstable/http; do not restore v3 @effect/platform/Http* imports.
• Use Effect.gen with yield* for generator workflows and Effect.fn("name")(function*() { ... }) when a named Effect-returning function is useful.
• Define services with Context.Service and explicit layers. V4 does not generate a default layer.
• Model expected failures as typed tagged errors and recover with Effect.catchTag/Effect.catchTags or Match, not manual _tag comparisons.
• Use Effect.tryPromise({ try, catch }) for fallible Promise boundaries.

Verification

For source-or-skill edits, run the narrow relevant checks:

bun scripts/build-framework.ts bun/effect
bun scripts/build-framework.ts node/effect

Run bun run verify when router or server behavior changes; it exercises the shared HTTP contract across the benchmark. After editing this skill, validate its frontmatter, metadata, JSON, and relative links.