@effected/semver

Strict SemVer 2.0.0 versions, ranges and comparators as Effect schemas. SemVer, Comparator and Range are Schema.Classes, so a version is a validated value with methods on it rather than a string you re-parse at every call site, and each one carries a FromString codec that decodes the canonical form and encodes back to it. Parsing is strict: no v prefix, no = prefix, no leading zeros on numeric identifiers, no partially consumed input. Every failure is a tagged error carrying the offending string and the character position where the grammar gave up. Zero runtime dependencies, no IO.

Pre-release. This package is part of the @effected/* kit, in pre-1.0.0 development against a single pinned Effect v4 prerelease. Packages graduate to 1.0.0 once Effect 4.0.0 ships. To hold your own effect versions at exactly the ones the kit is built and tested against, install @effected/pnpm-plugin-effect.

Stability: unstable. This package's API surface is not yet considered complete and may change across 0.x releases. Pin an exact version — even a package marked stable before 1.0.0 can introduce a breaking change by accident, and an exact pin turns that into a type-check error rather than a runtime surprise. Full policy: release strategy.

Why @effected/semver

The version parsers most projects reach for are lenient by default. They coerce v1.2.3 and =1.2.3 into a version, then hand back null — or throw — when they finally decide something is wrong, leaving you to reconstruct what failed and where. Once parsed, the result is a bag of numbers you stringify to store and re-parse to compare. This package inverts that. The class is the schema, so a version field anywhere in your own schemas decodes to a real SemVer and re-encodes to its canonical string with no glue code, and the operations you want live on the value you already have.

Failures are Schema.TaggedError values you route with Effect.catchTag, each one structured rather than stringly: InvalidVersionError carries input and position, UnsatisfiedRangeError carries the range and every version that was available to match against it. The strictness is deliberate. Coercion is a decision about your data taken inside a library you did not write, and it is where version bugs hide. Range.intersect holds the same line: intersecting ^1.0.0 with ^2.0.0 does not quietly hand back a range that matches nothing, it fails with UnsatisfiableConstraintError carrying both constraints. Nothing here repairs your input behind your back.

Install

npm install @effected/semver effect

pnpm add @effected/semver effect

Requires Node.js >=24.11.0.

All @effected/* packages are ESM-only: the exports maps publish only import conditions, so require() — including tools that resolve in CJS mode — fails with Node's ERR_PACKAGE_PATH_NOT_EXPORTED rather than loading a CJS build that does not exist. Import from an ES module.

effect v4 is the only peer dependency, and it is the only dependency of any kind — no parser, no polyfill, no platform package rides in behind it. There is no IO here, so there is nothing to provide at the edge either: the whole surface runs under Effect.runSync, apart from VersionCache, which brings its own layer.

Quick start

Parse, bump, compare, and test a version against a range:

import { Range, SemVer } from "@effected/semver";
import { Effect } from "effect";

const program = Effect.gen(function* () {
  const version = yield* SemVer.parse("1.2.3");
  const next = version.bump.minor();
  const range = yield* Range.parse("^1.0.0");
  return [next.toString(), range.test(version), version.gt(next)] as const;
});

console.log(Effect.runSync(program));
// => ["1.3.0", true, false]

Instance methods are the canonical API. Cross-cutting operations are dual statics on the owning class, so SemVer.gt(a, b) and a.pipe(SemVer.gt(b)) both typecheck and mean the same thing.

Versions

SemVer's fields are validated in the schema — non-negative safe integers for the components, well-formed prerelease and build identifiers — so SemVer.make cannot produce an invalid version. Use SemVer.parse for a string and SemVer.of(1, 2, 3) for the positional form.

import { SemVer } from "@effected/semver";
import { Effect } from "effect";

const program = Effect.gen(function* () {
  const stable = yield* SemVer.parse("1.0.0");
  const rc = yield* SemVer.parse("2.0.0-rc.1");
  return [
    stable.bump.prerelease("beta").toString(),
    rc.bump.prerelease().toString(),
    rc.isPrerelease,
    rc.truncate("prerelease").toString(),
  ] as const;
});

console.log(Effect.runSync(program));
// => ["1.0.1-beta.0", "2.0.0-rc.2", true, "2.0.0"]

Bumping is node-semver compatible: a stable version starts a prerelease of the next patch, switching identifiers resets the counter, and a trailing numeric identifier increments. Build metadata never survives a bump.

Equality follows the spec rather than the string. Equal.equals ignores build metadata (§10) and includes prerelease identifiers (§11), and SemVer overrides [Hash.symbol] to agree with that, so two versions differing only in build metadata are one value in a HashSet and one slot in VersionCache. SemVer.Order sorts by precedence; SemVer.OrderWithBuild adds a lexical tiebreak on build metadata when you need a total order over distinct version strings.

Collection operations are statics: sort, rsort, max, min, groupBy (by major, minor or patch), latestByMajor and latestByMinor.

Ranges and comparators

A Range is a union (OR) of comparator sets (AND). Parsing accepts the node-semver dialect — hyphen ranges, X-ranges, tilde, caret and || — desugars it into primitive comparators and normalizes the result. A Comparator is one operator applied to one complete version, with no wildcards and no sugar; that vocabulary belongs to Range.

import { Range, SemVer } from "@effected/semver";
import { Effect } from "effect";

const program = Effect.gen(function* () {
  const caret = yield* Range.parse("^1.0.0");
  const floor = yield* Range.parse(">=1.5.0");
  const both = yield* Range.intersect(caret, floor);
  const versions = [SemVer.of(1, 2, 0), SemVer.of(1, 6, 0), SemVer.of(2, 0, 0)];
  return [both.test(SemVer.of(1, 6, 0)), Range.filter(versions, caret).map((v) => v.toString())] as const;
});

console.log(Effect.runSync(program));
// => [true, ["1.2.0", "1.6.0"]]

Matching implements node-semver's prerelease restriction: a prerelease version satisfies a set only when some comparator in that set carries a prerelease on the same major.minor.patch tuple. That is what keeps ^1.2.3 from unexpectedly matching 1.2.4-alpha.

The range algebra is union, intersect, isSubset, equivalent and simplify. isSubset is a deliberate conservative approximation: it can report false for a range that is technically a subset, when the sub-range straddles comparator-set boundaries in the sup-range. False negatives are safe, because all they do is decline a simplification.

Comparing two versions

VersionDiff.between(a, b) classifies a change and carries the signed component deltas. It is a Schema.TaggedClass, so a diff serializes as cleanly as it computes.

import { SemVer, VersionDiff } from "@effected/semver";
import { Effect } from "effect";

const program = Effect.gen(function* () {
  const from = yield* SemVer.parse("1.2.3");
  const to = yield* SemVer.parse("2.0.0");
  const diff = VersionDiff.between(from, to);
  return [diff.type, diff.major, diff.toString()] as const;
});

console.log(Effect.runSync(program));
// => ["major", 1, "major (1.2.3 → 2.0.0)"]

type names the highest-precedence field that differs: "major", "minor", "patch", "prerelease", "build" or "none".

Version cache

VersionCache is a Context.Service over a sorted, deduplicated set of versions — pure state in a Ref, no IO. Reach for it when you hold a list of published versions and a range to resolve against them.

import { SemVer, VersionCache } from "@effected/semver";
import { Effect } from "effect";

const program = Effect.gen(function* () {
  const cache = yield* VersionCache;
  yield* cache.load([SemVer.of(1, 0, 0), SemVer.of(1, 4, 2), SemVer.of(2, 0, 0)]);
  const latest = yield* cache.latest();
  const resolved = yield* cache.resolveString("^1.0.0");
  return [latest.toString(), resolved.toString()] as const;
}).pipe(Effect.provide(VersionCache.layer));

console.log(Effect.runSync(program));
// => ["2.0.0", "1.4.2"]

The two kinds of absence stay apart. next and prev fail with VersionNotFoundError when the pivot version is not in the cache, and succeed with Option.none() when the pivot sits at a boundary. Queries over the whole cache (versions, filter) never fail and return [].

Errors

Every failure is a Schema.TaggedError routed with Effect.catchTag, carrying structured fields. The message getter is derived from those fields, never stored.

| Tag | Raised by | Carries | | --- | --------- | ------- | | InvalidVersionError | SemVer.parse | input, and the position where the grammar failed | | InvalidComparatorError | Comparator.parse | input, position | | InvalidRangeError | Range.parse, VersionCache.resolveString | input, position | | UnsatisfiableConstraintError | Range.intersect | constraints, the ranges whose intersection is empty | | EmptyCacheError | VersionCache.latest, VersionCache.oldest | nothing; the cache is empty | | VersionNotFoundError | VersionCache.diff, next, prev | version, the pivot that is not cached | | UnsatisfiedRangeError | VersionCache.resolve, resolveString | range, plus available, the versions that were there to match |

The FromString codecs report the same failures through a generic Schema parse error carrying the same message, so schema decoding and the parse statics never disagree about what is valid.

import { SemVer } from "@effected/semver";
import { Effect } from "effect";

// A leading `v` is not a version, and nothing here coerces it into one.
const program = SemVer.parse("v1.2.3").pipe(Effect.catch((error) => Effect.succeed(`${error._tag}: ${error.input}`)));

console.log(Effect.runSync(program));
// => "InvalidVersionError: v1.2.3"

Features

• SemVer — the version model: schema-validated fields, parse / of / make construction, bumping through version.bump, comparison as instance methods and dual statics, spec-correct Equal and Hash, and the collection statics (sort, max, groupBy, latestByMajor, …).
• Comparator — a single operator-plus-version constraint, and the primitive that range sugar desugars into.
• Range — the node-semver range dialect parsed into normalized comparator sets, with matching (test, filter, maxSatisfying, minSatisfying) and algebra (union, intersect, isSubset, equivalent, simplify).
• VersionDiff — the classified difference between two versions with signed component deltas, serializable as a tagged class.
• VersionCache — a sorted in-memory version set with range resolution and neighbor navigation, provided by VersionCache.layer.
• SemVer.FromString, Comparator.FromString, Range.FromString — codecs between the canonical strings and the models, usable as fields inside your own schemas.
• Seven tagged errors, each carrying the structured payload a caller needs to report what actually went wrong.

License

MIT