Array | helpers over JS arrays, readonly and non-empty arrays (map/sort/group/split/reduce) | transforming, grouping, or combining array-shaped collections immutably |
BigDecimal | arbitrary-precision decimal (bigint digits + scale) with arithmetic and formatting | exact decimal math for money/quantities where number rounding fails |
BigInt | helpers over native bigint: arithmetic, comparison, safe parsing to Option | working with bigint values and needing safe parse/aggregate/order |
Boolean | helpers over boolean: logical ops, lazy branching, ordering, reducing | combining booleans or choosing between lazy branches |
Brand | compile-time nominal tags on structurally-identical values, optionally validating | keeping Positive/UserId-style values from mixing without runtime cost |
Cache | concurrent cache of Effect lookup results with capacity/TTL and in-flight sharing | memoizing an effectful lookup by key with dedupe/expiry |
Cause | full structured failure record: typed errors, defects, interruptions, annotations | inspecting or formatting why an Effect failed without collapsing it |
Channel | low-level bidirectional streaming primitive underlying Stream and Sink | implementing custom stream operators; app code uses Stream/Sink instead |
ChannelSchema | schema encode/decode adapters wrapping a Channel's typed boundaries | crossing a channel boundary with schema-typed input/output |
Chunk | immutable ordered collection optimized for append/prepend/concat | building/transforming sequences without mutating the original |
Clock | service for reading current time (ms/nanos) and sleeping | time/sleep access you want to fake in tests via a service |
Combiner | strategy interface combine(a,b) for merging two same-type values (no identity) | passing a reusable merge rule; use Reducer if you need an empty value |
Config | declarative descriptions of config values decoded from a ConfigProvider | reading/validating typed configuration keys with defaults and fallbacks |
ConfigProvider | data sources (env, objects, .env, dirs) that feed raw values to Config | supplying or composing where Config reads its raw values from |
Console | Effect wrapper over console (log/group/count/table/timer) as a swappable service | logging/console side effects you want swappable in tests |
Context | typed map of service implementations keyed by Service/Reference | building or reading the service environment R of effects |
Cron | recurring calendar schedule from cron expressions or field constraints | matching dates or computing next/previous scheduled occurrences |
Crypto | platform-independent crypto service contract (random bytes, UUID, SHA digests) | secure random/UUID/hashing; contract, platform layer provides implementation |
Data | constructors for immutable value classes, tagged classes/unions, typed errors | defining _tag-carrying domain values and errors with structural equality |
DateTime | absolute instants plus optional time-zone-aware date-times and arithmetic | zone-aware timestamps, date math, and formatting |
Deferred | one-time set-once async variable many fibers can await | cross-fiber coordination on a single result/signal |
Differ | interface to compute/combine/apply patches describing value changes | modeling incremental patch-based updates to a value |
Duration | immutable time span (finite or infinite) for delays/timeouts/TTL | expressing delays, timeouts, intervals, or TTLs |
Effect | core Effect<A,E,R> type and the main API for building/running workflows | creating, composing, recovering, or running effectful programs |
Effectable | internal: prototype builder + base class to make custom values act as Effects | rarely — making a domain value yieldable in Effect.gen |
Encoding | Base64/Base64Url/hex encode/decode between strings, UTF-8, and bytes | converting to/from Base64/hex with Result-typed decode errors |
Equal | structural equality (equals) plus the Equal interface, guards, adapters | comparing values structurally or implementing custom equality |
Equivalence | reusable Equivalence<A> equality predicates and combinators | defining/combining custom same-type equality for a purpose |
ErrorReporter | forwards non-interruption Causes to a callback for logging/monitoring | routing Effect failures to external error-tracking systems |
ExecutionPlan | ordered fallback steps (context/layer + retries) tried until success | declaring fallback providers/retry tiers for effects or streams |
Exit | Exit<A,E> value form of a finished Effect (success or Cause failure) | inspecting/matching a completed Effect result synchronously as data |
Fiber | handle to a forked effect: await/join/interrupt, current fiber access | managing forked concurrent work and its lifecycle |
FiberHandle | scope-bound holder of at most one fiber, replacing/interrupting prior | tracking a single swappable background fiber tied to a scope |
FiberMap | scope-bound map of fibers keyed by K, auto-removed on completion | managing keyed background fibers under one scope |
FiberSet | scope-bound set of many fibers, all interrupted when scope closes | managing a dynamic group of background fibers under one scope |
FileSystem | portable file system service (read/write/stream/glob/watch), fails PlatformError | file IO; contract, platform layer provides implementation |
Filter | composable check returning Result (pass/fail) that can also narrow/transform | selective matching/recovery where a predicate must also refine or transform |
Formatter | renders arbitrary JS values to readable strings with redaction/cycle handling | formatting values for logs, diagnostics, or error messages |
Function | core composition helpers: pipe, flow, dual, identity/const/memoize | composing functions or writing dual direct/pipe APIs |
Graph | immutable/scoped-mutable indexed node+edge graph with traversal, paths, export | building/traversing a graph, shortest path, DAG, diagram export |
Hash | computes non-cryptographic structural hashes; interface for custom hash | implementing custom hashing for Equal-based collections |
HashMap | immutable key/value map (HAMT) keyed by structural equality | need immutable map with object/structural keys |
HashRing | weighted consistent-hashing ring keyed by PrimaryKey | routing keys/shards to nodes with minimal remapping |
HashSet | immutable set of unique values by Equal/Hash | need immutable set with structural-equality membership |
HKT | type-level: TypeLambda/Kind higher-kinded encoding | only when authoring generic type classes; agents skip |
Inspectable | internal: log/inspect formatting protocol for Effect values | implementing custom log/console/JSON rendering; rarely needed |
Iterable | lazy combinators over any [Symbol.iterator] value | transform/search/group iterables without materializing arrays |
JsonPatch | computes/applies deterministic RFC6902 add/remove/replace patches | diffing two JSON docs or replaying JSON changes |
JsonPointer | RFC6901 token escape/unescape helpers | escaping ~// in JSON Pointer path segments |
JsonSchema | normalize/convert JSON Schema & OpenAPI dialect documents | converting between Draft-07/2020-12/OpenAPI schemas, $ref resolution |
Latch | reusable open/closed fiber coordination primitive | gating fibers until an explicit open/release signal |
Layer | describes acquiring/wiring services with deps and errors | constructing and composing service dependencies |
LayerMap | keyed cache of scoped layer-built service contexts | per-tenant/per-region resource families built on demand |
LayerRef | refreshable single layer-built context with invalidation | share one scoped layer resource, rebuild on invalidate |
Logger | loggers, formatters, console/file routing, install layers | configuring/customizing how log events are emitted |
LogLevel | log-level types, ordering, threshold/enabled helpers | comparing or checking log severities |
ManagedRuntime | runs many effects against services built once from a Layer | bridging Effect to promise/callback/sync entry points |
Match | ordered pattern matcher (Match.type/Match.value) | pattern-matching on tags, shapes, predicates, literals |
MutableHashMap | in-place map mixing native and Equal/Hash keys | fast mutable map needing structural-key lookup |
MutableHashSet | in-place unique set built on MutableHashMap | fast mutable set with structural-equality members |
MutableList | in-place ordered list; append/prepend, drain from front | buffering values and draining FIFO in place |
MutableRef | synchronous in-place single-value reference | non-effectful mutable cell (vs Ref) |
Newtype | compile-time-only branded wrappers over a carrier type | distinguishing same-shape values (e.g. two string ids) |
NonEmptyIterable | type-level: Iterable branded as having ≥1 element | typing guaranteed-non-empty iterables; rarely imported directly |
Number | helpers over number: parse, math, compare, clamp, aggregate | numeric parsing, safe division, ordering, range checks |
Optic | lens/prism/optional focus for immutable read/update | reading/updating nested immutable structures without mutation |
Option | present/absent value Some/None, plus Option.gen | modeling optional values instead of null/undefined |
Order | comparison functions for ordered values | sorting, min/max, ranges, ordered structures |
Ordering | the -1/0/1 comparison result plus combinators | working with the output of an Order comparison |
PartitionedSemaphore | concurrency limiter over shared permits grouped by key | fair bounded concurrency across independent key groups |
Path | path ops service (join/normalize/parse/resolve); POSIX Path.layer built in | path manipulation; contract, platform layer provides (POSIX layer in core) |
Pipeable | internal: .pipe(...) method-chaining interface | only when authoring a pipeable data type; agents skip |
PlatformError | normalized platform error model (BadArgument/SystemError reasons) | typing/handling FileSystem/Terminal/subprocess/host IO failures |
Pool | shares scoped resources borrowed across fibers | pooling connections/clients with TTL and invalidation |
Predicate | runtime guards and refinements with combinators | type guards, tag/shape checks, composing predicates — never hand-write isString/object guards (NB: no isRecord on the v4 line; the record-ish guards are isObject/isReadonlyObject/isObjectOrArray) |
PrimaryKey | protocol exposing a stable string identifier | giving a value a stable string key (requests, ring nodes) |
PubSub | broadcast hub; each subscriber gets every message | fan-out messaging where subscribers don't compete |
Pull | internal: one low-level stream pull step (value/error/done) | only when writing custom Stream/Channel internals; agents skip |
Queue | async fiber-to-fiber queue; one consumer per value | backpressured/bounded work handoff between fibers |
Random | pseudo-random generator exposed as a replaceable Effect service | need effectful/seeded random numbers, shuffles, or deterministic test randomness |
RcMap | reference-counted map of scoped resources keyed, released when idle/unused | sharing per-key clients/connections/sessions with lifecycle, not general caching |
RcRef | reference-counted handle sharing one scoped resource across borrowers | share a single lazily-acquired resource; finalize when last borrower leaves |
Record | immutable helpers over plain string/symbol-keyed object dictionaries | working with {} dictionaries functionally: map/filter/merge/lookup without mutation |
Redactable | protocol for context-aware alternate representations of sensitive objects | building a type that masks itself in logs/traces/serialization |
Redacted | wrapper hiding a value in string/JSON/inspect output while retaining it | carry secrets/tokens through code without leaking them in diagnostics |
Reducer | Combiner plus an initial value and fold-an-iterable operation | fold many values into one with an identity/empty case |
Ref | fiber-safe mutable cell with effectful get/set/update/modify | hold shared mutable state that composes with Effect concurrency |
References | built-in Context.Reference runtime keys (concurrency, logging, tracing) | read or override runtime execution/diagnostic settings for an effect |
RegExp | native RegExp constructor, guard, and literal-escaping helper | build patterns from data-driven text or narrow unknown to RegExp |
Request | typed request value describing one data-load with error/requirements | define a batchable/cacheable data query for Effect.request |
RequestResolver | resolver that batches, groups, and completes pending Request entries | implement backend batching/dedup/caching behind Effect.request |
Resource | refreshable scoped value caching last acquisition, auto/manual refresh | cache a scoped value that must refresh on schedule or on demand |
Result | plain Success/Failure data holding an already-computed outcome | represent a settled success-or-error value without running effects (v4's Either successor) |
Runtime | low-level makeRunMain for turning an Effect into a process entry point | writing a platform runner; app code uses platform-provided runners instead |
Schedule | policy stepping inputs into outputs plus delays for retry/repeat/pace | decide when/how often to retry, repeat, or pace an effect |
Scheduler | controls how runnable fiber tasks are queued, dispatched, and yielded | internal/advanced: tune or disable fiber scheduling and yields — usually skip |
Schema | validate/decode/encode data shapes with codecs, classes, refinements | the primary entry point for any schema, codec, or data validation |
SchemaAST | runtime tree representation of schemas (nodes, checks, annotations) | advanced machinery: inspect/build/rewrite schema ASTs programmatically |
SchemaGetter | one-way optional-in/optional-out conversions used inside transformations | consumer-facing when authoring a custom decode/encode direction |
SchemaIssue | describes and formats decode/encode/check failures with location | consumer-facing: inspect or format schema validation errors |
SchemaParser | runs a schema against values (decode/encode/validate) in many result styles | consumer-facing: execute a schema returning Effect/Exit/Option/Result/sync |
SchemaRepresentation | JSON-serializable descriptions of schemas plus TS-codegen | machinery: serialize schemas, convert to/from JSON Schema, generate code |
SchemaTransformation | two-way encode/decode conversions connecting two representations | consumer-facing when building a custom bidirectional codec |
SchemaUtils | specialized schema helpers too niche for core Schema | internal/advanced — usually skip |
Scope | lifetime boundary collecting finalizers run with an Exit on close | directly create/fork/close scopes; most code uses Effect.scoped/Layer |
ScopedCache | cache whose entries own scopes, releasing resources on eviction | cache resource-backed values with per-entry cleanup and expiry |
ScopedRef | current value plus the scope owning it; swaps acquire/release atomically | hold a swappable resource handle (client/connection) with clean replacement |
Semaphore | permit pool limiting concurrent access to a shared resource | bound concurrency around an effect via acquire/release of permits |
Sink | stream consumer folding/collecting a Stream's output into one result | terminating a Stream: collect, fold, count, or search its elements |
Stdio | argv and stdin/stdout/stderr of the CURRENT process as an Effect service | standard-IO access (not spawning); contract, platform layer provides |
Stream | effectful source emitting many values over time with error/requirements | model pull-based/streaming data: queues, callbacks, files, paginated sources |
String | pipe-friendly helpers over TypeScript string values | functional string ops: trim/case/slice/replace/Option-returning search |
Struct | immutable helpers over plain TypeScript objects (pick/omit/rename) | transform object shapes functionally and derive comparisons |
SubscriptionRef | Ref that publishes every committed change as a changes stream | hold state others must observe reactively over time |
Symbol | runtime predicate narrowing unknown to a primitive symbol | guarding an unknown before using it as a symbol key/discriminant |
SynchronizedRef | Ref whose updates run one-at-a-time, safe for effectful transitions | serialize state updates when the next value is computed by an effect |
Take | stored representation of one stream pull: batch, failure, or done | low-level stream plumbing: inspecting buffered pull results |
Terminal | interactive terminal service (size, line/key input, output) | terminal capabilities; contract, platform layer provides |
Tracer | low-level span/tracing model and tracer service | define/inspect spans or a custom tracer; usually via higher-level tracing APIs |
Trie | immutable string-keyed prefix tree for prefix/longest-match lookup | autocomplete, route tables, dictionaries, prefix-based key lookup |
Tuple | immutable helpers over fixed-length arrays preserving element positions | build/transform positional tuples and derive tuple comparisons |
TxChunk | transactional Chunk stored in a TxRef | STM-family: atomic sequence/buffer updates within a transaction |
TxDeferred | write-once transactional cell completing to a Result, retrying readers | STM-family: coordinate/await a one-shot value across transactions |
TxHashMap | transactional HashMap in a TxRef | STM-family: atomic keyed registry/counter/index updates |
TxHashSet | transactional HashSet in a TxRef | STM-family: atomic set membership changes alongside other state |
TxPriorityQueue | transactional priority queue ordered by an Order, retrying take/peek | STM-family: ordered coordination queue with transactional waiting |
TxPubSub | transactional publish/subscribe hub over TxQueue subscribers | STM-family: broadcast values atomically within transactions |
TxQueue | transactional queue with enqueue/dequeue handles, retrying when blocked | STM-family: coordinate producers/consumers within transactions |
TxReentrantLock | transactional reentrant read/write lock tracked by fiber | STM-family: shared/exclusive locking that composes in transactions |
TxRef | core transactional reference journaled and committed via Effect.tx | STM-family: the base transactional cell all Tx collections build on |
TxSemaphore | transactional fixed-capacity permit pool in a TxRef | STM-family: permit acquisition that commits with other transactional state |
TxSubscriptionRef | transactional Ref publishing committed changes to subscribers | STM-family: observable transactional state with current-value replay |
Types | compile-time-only utility types (tuples, unions, variance, mutability) | type-level plumbing — no runtime; agents skip unless authoring types |
UndefinedOr | helpers for plain A | undefined values | handle optionality with undefined without wrapping in Option |
Unify | type-level unification protocol collapsing unions to public data types | maintainer/advanced type plumbing — skip |
Utils | internal generator machinery behind Effect.gen/HKT | internal — skip |
testing/FastCheck | re-export of fast-check for property-based testing | generate random inputs for property tests alongside Effect helpers |
testing/TestClock | controllable Clock service driving virtual time | make sleep/timeout/schedule/retry tests deterministic by advancing time |
testing/TestConsole | test Console capturing log/error calls in memory | assert on console output deterministically in tests |
testing/TestSchema | assertions for schema construct/decode/encode/arbitrary/round-trip | testing that a schema decodes, encodes, and round-trips correctly |
