[effect-bot]

Adds a value-oriented YAML printer to effect/encoding/Yaml, stage 2 of the YAML expansion plan.

API

Yaml.stringify(value: unknown, options?: { readonly indent?: number | undefined }): Result<string, EncodingError>
Yaml.stringifyAll(values: Iterable<unknown>, options?: { readonly indent?: number | undefined }): Result<string, EncodingError>

Contract

• null, booleans, numbers, strings, arrays, and plain objects. Block style, insertion-order keys, {} and [] for empty collections, output ends in one newline.
• A string prints plain only when parse and the YAML 1.2 core schema both read it back as the same string; otherwise it is double-quoted with YAML escapes. Keys follow the same rule, so "true": and "1": stay strings.
• Multiline strings print as |, |-, or |+ literal block scalars when no line has surrounding whitespace or control characters; otherwise double-quoted.
• .inf, -.inf, .nan, and -0.0 round-trip, including the sign of zero.
• Like JSON.stringify: toJSON is applied first, undefined properties are omitted, undefined items print null, symbol keys are ignored.
• Unlike JSON.stringify, nothing is silently dropped or turned into {}: bigints, functions, symbols, objects with a non-plain prototype and no toJSON, and cycles fail with an EncodingError whose message names the path (value.items[0], value[1].id in a stream).
• Nested sequences print in the two-line form (- then an indented - item) because the current parser does not read - - item; shared references print inline each time, no anchors.

Integration with the parser stack

The printer commits were written on v4/next-minor before the parser stages landed. The last commit on this branch merges them into the stage 5 head (#10285), so this PR's diff shows the printer as it fits on the finished parser. The merge had two conflicts, both from the two sides adding code next to each other:

• The Yaml.ts module header and the end of the file keep the parser stack's text, then add the printer code. The printer branch's older parse definition was dropped because the parser stack already has the current one.
• The Yaml.test.ts stringify tests follow the parser tests.

Validation

• vitest packages/effect/test/encoding/Yaml.test.ts: 195 passed (35 new printer tests, committed in the tests-first run, plus the existing 160).
• Every printer output in the test file is also checked against the yaml 2.9.1 reference parser, added as a devDependency of packages/effect for that purpose.
• Ad hoc: 49 representative values at indents 1, 2, and 4 round-trip through Yaml.parse unchanged.
• tsc for packages/effect, oxlint, dprint, pnpm jsdocs --check, doctests for the module, and pnpm circular all pass.

Stack

These PRs form one stack. Each targets the PR before it, so its diff shows only its own stage. Merge them in this order:

1. Add Yaml.parseAll and return Result from Yaml.parse #10271: Yaml.parseAll and Result from Yaml.parse (merged)
2. Reject Yaml tags and explicit keys, resolve alias keys, and keep non-space white space #10276: parser hardening, based on v4/next-minor
3. Parse Yaml compact nested sequences and multiline quoted flow scalars #10279: compact nested sequences and multiline quoted flow scalars, based on Reject Yaml tags and explicit keys, resolve alias keys, and keep non-space white space #10276
4. Treat a tab after a Yaml sequence dash as separation #10282: tab after a sequence dash, based on Parse Yaml compact nested sequences and multiline quoted flow scalars #10279
5. Accept escaped literal tabs in Yaml double-quoted scalars #10283: escaped literal tabs, based on Treat a tab after a Yaml sequence dash as separation #10282
6. Reject Yaml flow plain scalars starting with a dash and separation #10284: flow plain scalars starting with a dash, based on Accept escaped literal tabs in Yaml double-quoted scalars #10283
7. Resolve Yaml core schema tags #10285: core schema tags, based on Reject Yaml flow plain scalars starting with a dash and separation #10284
8. Add Yaml.stringify and Yaml.stringifyAll #10272: Yaml.stringify and Yaml.stringifyAll, based on Resolve Yaml core schema tags #10285 (this PR)
9. Harden and extend Yaml parsing and add Yaml.stringify #10287: printer round-trip through Yaml.parse, based on Add Yaml.stringify and Yaml.stringifyAll #10272

After a PR in the stack is squash-merged, the next one has to be rebased onto the squash commit and retargeted to v4/next-minor before it can merge.

Closes EFF-3232

[changeset-bot]

🦋 Changeset detected

Latest commit: 3b465fb

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 33 packages

Name	Type
effect	Minor
@effect/opentelemetry	Minor
@effect/vitest	Minor
@effect/ai-anthropic	Minor
@effect/ai-cloudflare	Minor
@effect/ai-openai-compat	Minor
@effect/ai-openai	Minor
@effect/ai-openrouter	Minor
@effect/ai-typesafe	Minor
@effect/atom-react	Minor
@effect/atom-solid	Minor
@effect/atom-vue	Minor
@effect/platform-browser	Minor
@effect/platform-bun	Minor
@effect/platform-deno	Minor
@effect/platform-node-shared	Minor
@effect/platform-node	Minor
@effect/sql-clickhouse	Minor
@effect/sql-d1	Minor
@effect/sql-libsql	Minor
@effect/sql-mssql	Minor
@effect/sql-mysql2	Minor
@effect/sql-pg	Minor
@effect/sql-pglite	Minor
@effect/sql-sqlite-bun	Minor
@effect/sql-sqlite-do	Minor
@effect/sql-sqlite-node	Minor
@effect/sql-sqlite-react-native	Minor
@effect/sql-sqlite-wasm	Minor
@effect/docgen	Minor
@effect/doctest	Minor
@effect/graphql-generator	Minor
@effect/openapi-generator	Minor

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[github-actions]

Bundle Size Analysis

Generated from PR build output; treat the content below as untrusted.

File Name	Current Size	Previous Size	Difference
arbitrary-combinators.ts	39.41 KB	39.41 KB	0.00 KB (0.00%)
basic.ts	7.23 KB	7.23 KB	0.00 KB (0.00%)
batching.ts	11.08 KB	11.08 KB	0.00 KB (0.00%)
brand.ts	6.87 KB	6.87 KB	0.00 KB (0.00%)
cache.ts	11.54 KB	11.54 KB	0.00 KB (0.00%)
config.ts	22.84 KB	22.84 KB	0.00 KB (0.00%)
differ.ts	22.00 KB	22.00 KB	0.00 KB (0.00%)
http-client.ts	27.12 KB	27.12 KB	0.00 KB (0.00%)
http-router.ts	37.04 KB	37.04 KB	0.00 KB (0.00%)
logger.ts	12.01 KB	12.01 KB	0.00 KB (0.00%)
metric.ts	9.47 KB	9.47 KB	0.00 KB (0.00%)
optic.ts	7.10 KB	7.10 KB	0.00 KB (0.00%)
pubsub.ts	16.02 KB	16.02 KB	0.00 KB (0.00%)
queue.ts	12.89 KB	12.89 KB	0.00 KB (0.00%)
schedule.ts	11.80 KB	11.80 KB	0.00 KB (0.00%)
schema-bigdecimal.ts	14.14 KB	14.14 KB	0.00 KB (0.00%)
schema-binary.ts	41.99 KB	41.99 KB	0.00 KB (0.00%)
schema-class.ts	21.73 KB	21.73 KB	0.00 KB (0.00%)
schema-fromJsonSchemaDocument.ts	29.60 KB	29.60 KB	0.00 KB (0.00%)
schema-representation-roundtrip.ts	27.99 KB	27.99 KB	0.00 KB (0.00%)
schema-string-transformation.ts	15.35 KB	15.35 KB	0.00 KB (0.00%)
schema-string.ts	12.34 KB	12.34 KB	0.00 KB (0.00%)
schema-template-literal.ts	16.27 KB	16.27 KB	0.00 KB (0.00%)
schema-toArbitrary.ts	38.95 KB	38.95 KB	0.00 KB (0.00%)
schema-toCodeDocument.ts	26.15 KB	26.15 KB	0.00 KB (0.00%)
schema-toCodecJson.ts	20.90 KB	20.90 KB	0.00 KB (0.00%)
schema-toEquivalence.ts	21.05 KB	21.05 KB	0.00 KB (0.00%)
schema-toFormatter.ts	21.14 KB	21.14 KB	0.00 KB (0.00%)
schema-toJsonSchemaDocument.ts	26.17 KB	26.17 KB	0.00 KB (0.00%)
schema-toRepresentation.ts	21.23 KB	21.23 KB	0.00 KB (0.00%)
schema.ts	20.82 KB	20.82 KB	0.00 KB (0.00%)
stm.ts	14.20 KB	14.20 KB	0.00 KB (0.00%)
stream.ts	10.38 KB	10.38 KB	0.00 KB (0.00%)

[effect-bot]

Superseded by #10287, which now holds the rest of the YAML expansion as one PR against v4/next-minor. This PR's commits are included there unchanged.