Show HN: Config parser written in TypeScript types

A SOML parser, encoder, and canonicalizer written entirely in TypeScript types

Your TypeScript compiler parses the document, validates its values, and infers the result. It can even encode and canonicalize SOML, including integer radix conversion, nanosecond duration arithmetic, and UTC date rollover. Zero runtime code. Just import type.

npm install soml-typescript-types

Requires TypeScript 7 or later with strictNullChecks enabled.

Parse<Source, Options>

Parse a SOML string literal into its value type. Supports objects, arrays, comments, block strings, numeric and temporal scalars, and up to 100 nested collections. Invalid input returns SomlError.

import type {Parse} from 'soml-typescript-types';

type Configuration = Parse<name: 'api-gateway' port: 8080 healthy: true, {integers: 'bigint'}>; //=> {name: 'api-gateway'; port: 8080n; healthy: true}

Encode<Value, Options>

Encode literal scalars, finite tuples, and object types with required members as a SOML string literal. Keys are sorted. Use canonical: true to normalize scalars, indent with tabs, and add a final LF; canonical documents must be objects or arrays. Unsupported values return SomlError.

Private or protected constructors that shadow built-in function members are unsupported because their construct signatures are hidden from conditional type checks.

import type {Encode} from 'soml-typescript-types';

type Source = Encode<{port: 8080n; healthy: true}>; //=> '{healthy: true, port: 8080}'

Temporal values use their branded types:

import type {Encode, SomlDate} from 'soml-typescript-types';

type Source = Encode<{day: SomlDate<'1582-10-10'>}>; //=> '{day: 1582-10-10}'

Canonicalize<Source, Options>

Parse and normalize a SOML document into its canonical string literal. Accepts the same options as Parse. Invalid or unencodable input returns SomlError.

import type {Canonicalize} from 'soml-typescript-types';

type Source = Canonicalize<"z: 0xFF\na: 90m">; //=> 'a: 1h30m\nz: 255\n'

Options and values

integers: 'bigint' infers exact bigint literals across the full signed int64 range. The default, 'source', preserves spelling as SomlInteger<Source>.

maxDepth lowers the nesting limit from 100. Each object or array counts as one level, including the root.

SomlDate<Source> (also exported as Date<Source>) preserves exact proleptic Gregorian YYYY-MM-DD spelling in years 0001 to 9999, without a time or timezone. It is distinct from strings and instants. Import SomlDate when the module also uses the global Date type, because the alias shadows it.

SomlInstant<Source> and SomlDuration<Source> preserve temporal spelling. Canonical encoding normalizes instants to UTC and durations to hours, minutes, and seconds.

Floats infer as number literals where possible. number literals encode as floats; use bigint or SomlInteger for integers.

SomlError includes a reason; source positions are not tracked. Unions containing an invalid alternative return only diagnostics. A widened source string returns a general value model.

Limitations

Note

Unicode escape decoding (\u{…}), Unicode scalar validation, and non-ASCII key encoding are unsupported. Literal Unicode string values and quoted input keys are preserved. C0 controls other than tab and LF, and U+007F, cannot be encoded.

This works on types, not runtime input or UTF-8 bytes. Encoding requires concrete values: widened primitives, open arrays, optional members, and index signatures cannot identify one encoding. Rounded floats can widen to number, preventing encoding or canonicalization. There is no fixed character cap, but TypeScript's compiler resource limits still apply.

Option values must be concrete literals. Widened or ambiguous option types are unsupported to keep this compile-time API simple.

Structurally subsumed unions wrapped in NoInfer are unsupported because TypeScript can collapse their alternatives during inference.

See the SOML specification and type declarations for details.

Some people climb mountains. Some people build ships in bottles. Some people teach the TypeScript compiler to do nanosecond duration arithmetic and UTC date rollover using nothing but conditional types and spite. We all cope differently.

If you still think it is dumb, you are probably right. It is also tested against the SOML conformance corpus.

npm test checks the types and conformance runner. npm run bench measures compiler cost. npm run test:conformance checks the sibling ../soml-javascript/test/conformance corpus, including explicit diagnostics for unsupported Unicode features. The scripts require Node.js 26 or later.

npm run test:stress runs generated parser, encoder, and scalar checks against the sibling runtime parser and serializer and independent Date and bigint calculations. Pass different runtime parser and serializer module paths after -- if needed.