<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>(
self: Channel<
ReadonlyArray<OutElem>,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env
>
): Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>Flattens a channel that outputs arrays into a channel that outputs individual elements.
Example (Flattening arrays of channel output)
import { Channel, Data } from "effect"
class FlattenError extends Data.TaggedError("FlattenError")<{
readonly message: string
}> {}
// Create a channel that outputs arrays
const arrayChannel = Channel.fromIterable([
[1, 2, 3],
[4, 5],
[6, 7, 8, 9]
])
// Flatten the arrays into individual elements
const flattenedChannel = Channel.flattenArray(arrayChannel)
// Outputs: 1, 2, 3, 4, 5, 6, 7, 8, 9transforming
Source effect/Channel.ts:291238 lines
export const const flattenArray: <
OutElem,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env
>(
self: Channel<
ReadonlyArray<OutElem>,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env
>
) => Channel<
OutElem,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env
>
Flattens a channel that outputs arrays into a channel that outputs individual elements.
Example (Flattening arrays of channel output)
import { Channel, Data } from "effect"
class FlattenError extends Data.TaggedError("FlattenError")<{
readonly message: string
}> {}
// Create a channel that outputs arrays
const arrayChannel = Channel.fromIterable([
[1, 2, 3],
[4, 5],
[6, 7, 8, 9]
])
// Flatten the arrays into individual elements
const flattenedChannel = Channel.flattenArray(arrayChannel)
// Outputs: 1, 2, 3, 4, 5, 6, 7, 8, 9
flattenArray = <
function (type parameter) OutElem in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<ReadonlyArray<OutElem>, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>OutElem,
function (type parameter) OutErr in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<ReadonlyArray<OutElem>, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>OutErr,
function (type parameter) OutDone in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<ReadonlyArray<OutElem>, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>OutDone,
function (type parameter) InElem in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<ReadonlyArray<OutElem>, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>InElem,
function (type parameter) InErr in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<ReadonlyArray<OutElem>, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>InErr,
function (type parameter) InDone in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<ReadonlyArray<OutElem>, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>InDone,
function (type parameter) Env in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<ReadonlyArray<OutElem>, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>Env
>(
self: Channel<
ReadonlyArray<OutElem>,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env
>
(parameter) self: {
pipe: { <A>(this: A): A; <A, B = never>(this: A, ab: (_: A) => B): B; <A, B = never, C = never>(this: A, ab: (_: A) => B, bc: (_: B) => C): C; <A, B = never, C = never, D = never>(this: A, ab: (_: A) => B, bc: (_: B) => C, cd: (_: C) => D): D; <…;
}
interface Channel<out OutElem, out OutErr = never, out OutDone = void, in InElem = unknown, in InErr = unknown, in InDone = unknown, out Env = never>A Channel is a nexus of I/O operations, which supports both reading and
writing. A channel may read values of type InElem and write values of type
OutElem. When the channel finishes, it yields a value of type OutDone. A
channel may fail with a value of type OutErr.
Details
Channels are the foundation of Streams: both streams and sinks are built on
channels. Most users shouldn't have to use channels directly, as streams and
sinks are much more convenient and cover all common use cases. However, when
adding new stream and sink operators, or doing something highly specialized,
it may be useful to use channels directly.
Channels compose in a variety of ways:
- Piping: One channel can be piped to another channel, assuming the
input type of the second is the same as the output type of the first.
- Sequencing: The terminal value of one channel can be used to create
another channel, and both the first channel and the function that makes
the second channel can be composed into a channel.
- Concatenating: The output of one channel can be used to create other
channels, which are all concatenated together. The first channel and the
function that makes the other channels can be composed into a channel.
Example (Typing channels)
import type { Channel } from "effect"
// A channel that outputs numbers and requires no environment
type NumberChannel = Channel.Channel<number>
// A channel that outputs strings, can fail with Error, completes with boolean
type StringChannel = Channel.Channel<string, Error, boolean>
// A channel with all type parameters specified
type FullChannel = Channel.Channel<
string, // OutElem - output elements
Error, // OutErr - output errors
number, // OutDone - completion value
number, // InElem - input elements
string, // InErr - input errors
boolean, // InDone - input completion
{ db: string } // Env - required environment
>
Channel<interface ReadonlyArray<T>ReadonlyArray<function (type parameter) OutElem in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<ReadonlyArray<OutElem>, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>OutElem>, function (type parameter) OutErr in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<ReadonlyArray<OutElem>, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>OutErr, function (type parameter) OutDone in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<ReadonlyArray<OutElem>, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>OutDone, function (type parameter) InElem in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<ReadonlyArray<OutElem>, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>InElem, function (type parameter) InErr in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<ReadonlyArray<OutElem>, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>InErr, function (type parameter) InDone in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<ReadonlyArray<OutElem>, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>InDone, function (type parameter) Env in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<ReadonlyArray<OutElem>, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>Env>
): interface Channel<out OutElem, out OutErr = never, out OutDone = void, in InElem = unknown, in InErr = unknown, in InDone = unknown, out Env = never>A Channel is a nexus of I/O operations, which supports both reading and
writing. A channel may read values of type InElem and write values of type
OutElem. When the channel finishes, it yields a value of type OutDone. A
channel may fail with a value of type OutErr.
Details
Channels are the foundation of Streams: both streams and sinks are built on
channels. Most users shouldn't have to use channels directly, as streams and
sinks are much more convenient and cover all common use cases. However, when
adding new stream and sink operators, or doing something highly specialized,
it may be useful to use channels directly.
Channels compose in a variety of ways:
- Piping: One channel can be piped to another channel, assuming the
input type of the second is the same as the output type of the first.
- Sequencing: The terminal value of one channel can be used to create
another channel, and both the first channel and the function that makes
the second channel can be composed into a channel.
- Concatenating: The output of one channel can be used to create other
channels, which are all concatenated together. The first channel and the
function that makes the other channels can be composed into a channel.
Example (Typing channels)
import type { Channel } from "effect"
// A channel that outputs numbers and requires no environment
type NumberChannel = Channel.Channel<number>
// A channel that outputs strings, can fail with Error, completes with boolean
type StringChannel = Channel.Channel<string, Error, boolean>
// A channel with all type parameters specified
type FullChannel = Channel.Channel<
string, // OutElem - output elements
Error, // OutErr - output errors
number, // OutDone - completion value
number, // InElem - input elements
string, // InErr - input errors
boolean, // InDone - input completion
{ db: string } // Env - required environment
>
Channel<function (type parameter) OutElem in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<ReadonlyArray<OutElem>, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>OutElem, function (type parameter) OutErr in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<ReadonlyArray<OutElem>, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>OutErr, function (type parameter) OutDone in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<ReadonlyArray<OutElem>, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>OutDone, function (type parameter) InElem in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<ReadonlyArray<OutElem>, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>InElem, function (type parameter) InErr in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<ReadonlyArray<OutElem>, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>InErr, function (type parameter) InDone in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<ReadonlyArray<OutElem>, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>InDone, function (type parameter) Env in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<ReadonlyArray<OutElem>, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>Env> =>
const transformPull: <
OutElem,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env,
OutElem2,
OutErr2,
OutDone2,
Env2,
OutErrX,
EnvX
>(
self: Channel<
OutElem,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env
>,
f: (
pull: Pull.Pull<OutElem, OutErr, OutDone>,
scope: Scope.Scope
) => Effect.Effect<
Pull.Pull<OutElem2, OutErr2, OutDone2, Env2>,
OutErrX,
EnvX
>
) => Channel<
OutElem2,
Pull.ExcludeDone<OutErr2> | OutErrX,
OutDone2,
InElem,
InErr,
InDone,
Env | Env2 | EnvX
>
Transforms a Channel by applying a function to its Pull implementation.
Example (Transforming pull behavior)
import { Channel, Effect } from "effect"
// Transform a channel by modifying its pull behavior
const originalChannel = Channel.fromIterable([1, 2, 3])
const transformedChannel = Channel.transformPull(
originalChannel,
(pull, scope) =>
Effect.succeed(
Effect.map(pull, (value) => value * 2)
)
)
// Outputs: 2, 4, 6
transformPull(self: Channel<
ReadonlyArray<OutElem>,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env
>
(parameter) self: {
pipe: { <A>(this: A): A; <A, B = never>(this: A, ab: (_: A) => B): B; <A, B = never, C = never>(this: A, ab: (_: A) => B, bc: (_: B) => C): C; <A, B = never, C = never, D = never>(this: A, ab: (_: A) => B, bc: (_: B) => C, cd: (_: C) => D): D; <…;
}
pull: Pull.Pull<
ReadonlyArray<OutElem>,
OutErr,
OutDone,
never
>
(parameter) pull: {
pipe: { <A>(this: A): A; <A, B = never>(this: A, ab: (_: A) => B): B; <A, B = never, C = never>(this: A, ab: (_: A) => B, bc: (_: B) => C): C; <A, B = never, C = never, D = never>(this: A, ab: (_: A) => B, bc: (_: B) => C, cd: (_: C) => D): D; <…;
toString: () => string;
toJSON: () => unknown;
}
let array: readonly OutElem[] | undefinedarray: interface ReadonlyArray<T>ReadonlyArray<function (type parameter) OutElem in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<ReadonlyArray<OutElem>, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>OutElem> | undefined
let let index: numberindex = 0
const const pump: Effect.Effect<
OutElem,
OutErr | Cause.Done<OutDone>,
never
>
const pump: {
pipe: { <A>(this: A): A; <A, B = never>(this: A, ab: (_: A) => B): B; <A, B = never, C = never>(this: A, ab: (_: A) => B, bc: (_: B) => C): C; <A, B = never, C = never, D = never>(this: A, ab: (_: A) => B, bc: (_: B) => C, cd: (_: C) => D): D; <…;
toString: () => string;
toJSON: () => unknown;
}
import EffectEffect.const suspend: <A, E, R>(
effect: LazyArg<Effect<A, E, R>>
) => Effect<A, E, R>
Creates an Effect lazily, delaying construction until it is needed.
When to use
Use when you need to defer the evaluation of an effect until it is required.
Details
suspend takes a thunk that represents an effect and delays creating it
until the suspended effect is evaluated. This is useful for optimizing
expensive computations, managing circular dependencies such as recursive
functions, and helping TypeScript unify return types when branches construct
different effects. Any side effects or scoped captures inside the thunk are
re-executed on each invocation.
Example (Lazily evaluating side effects)
import { Effect } from "effect"
let i = 0
const bad = Effect.succeed(i++)
const good = Effect.suspend(() => Effect.succeed(i++))
console.log(Effect.runSync(bad)) // Output: 0
console.log(Effect.runSync(bad)) // Output: 0
console.log(Effect.runSync(good)) // Output: 1
console.log(Effect.runSync(good)) // Output: 2
Example (Suspending recursive Fibonacci evaluation)
import { Effect } from "effect"
const blowsUp = (n: number): Effect.Effect<number> =>
n < 2
? Effect.succeed(1)
: Effect.zipWith(blowsUp(n - 1), blowsUp(n - 2), (a, b) => a + b)
// console.log(Effect.runSync(blowsUp(32)))
// crash: JavaScript heap out of memory
const allGood = (n: number): Effect.Effect<number> =>
n < 2
? Effect.succeed(1)
: Effect.zipWith(
Effect.suspend(() => allGood(n - 1)),
Effect.suspend(() => allGood(n - 2)),
(a, b) => a + b
)
console.log(Effect.runSync(allGood(32)))
// Output: 3524578
Example (Helping TypeScript infer recursive effect types)
import { Effect } from "effect"
// Without suspend, TypeScript may struggle with type inference.
// Inferred type:
// (a: number, b: number) =>
// Effect<never, Error, never> | Effect<number, never, never>
const withoutSuspend = (a: number, b: number) =>
b === 0
? Effect.fail(new Error("Cannot divide by zero"))
: Effect.succeed(a / b)
// Using suspend to unify return types.
// Inferred type:
// (a: number, b: number) => Effect<number, Error, never>
const withSuspend = (a: number, b: number) =>
Effect.suspend(() =>
b === 0
? Effect.fail(new Error("Cannot divide by zero"))
: Effect.succeed(a / b)
)
suspend(function function (local function) loop(): Pull.Pull<OutElem, OutErr, OutDone>loop(): import PullPull.interface Pull<out A, out E = never, out Done = void, out R = never>An effectful pull step that either produces a value, fails with E, or
signals completion with Cause.Done<Done>.
When to use
Use to model one low-level pull step when a consumer repeatedly evaluates an
effect that may emit a value, fail normally, or signal normal completion
through Cause.Done.
Details
Pull represents completion in the error channel so low-level stream
consumers can distinguish ordinary failures from end-of-input and carry a
leftover value when needed.
Pull<function (type parameter) OutElem in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<ReadonlyArray<OutElem>, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>OutElem, function (type parameter) OutErr in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<ReadonlyArray<OutElem>, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>OutErr, function (type parameter) OutDone in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<ReadonlyArray<OutElem>, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>OutDone> {
if (let array: readonly OutElem[] | undefinedarray === var undefinedundefined) {
return import EffectEffect.const flatMap: {
<A, B, E1, R1>(
f: (a: A) => Effect<B, E1, R1>
): <E, R>(
self: Effect<A, E, R>
) => Effect<B, E1 | E, R1 | R>
<A, E, R, B, E1, R1>(
self: Effect<A, E, R>,
f: (a: A) => Effect<B, E1, R1>
): Effect<B, E | E1, R | R1>
}
pull: Pull.Pull<
ReadonlyArray<OutElem>,
OutErr,
OutDone,
never
>
(parameter) pull: {
pipe: { <A>(this: A): A; <A, B = never>(this: A, ab: (_: A) => B): B; <A, B = never, C = never>(this: A, ab: (_: A) => B, bc: (_: B) => C): C; <A, B = never, C = never, D = never>(this: A, ab: (_: A) => B, bc: (_: B) => C, cd: (_: C) => D): D; <…;
toString: () => string;
toJSON: () => unknown;
}
array_: readonly OutElem[]array_) => {
switch (array_: readonly OutElem[]array_.ReadonlyArray<T>.length: numberGets the length of the array. This is a number one higher than the highest element defined in an array.
length) {
case 0:
return function (local function) loop(): Pull.Pull<OutElem, OutErr, OutDone>loop()
case 1:
return import EffectEffect.const succeed: <A>(value: A) => Effect<A>Creates an Effect that always succeeds with a given value.
When to use
Use when an effect should complete successfully with a specific value without any errors
or external dependencies.
Example (Creating a successful effect)
import { Effect } from "effect"
// Creating an effect that represents a successful scenario
//
// ┌─── Effect<number, never, never>
// ▼
const success = Effect.succeed(42)
succeed(array_: readonly OutElem[]array_[0])
default: {
let array: readonly OutElem[] | undefinedarray = array_: readonly OutElem[]array_
return import EffectEffect.const succeed: <A>(value: A) => Effect<A>Creates an Effect that always succeeds with a given value.
When to use
Use when an effect should complete successfully with a specific value without any errors
or external dependencies.
Example (Creating a successful effect)
import { Effect } from "effect"
// Creating an effect that represents a successful scenario
//
// ┌─── Effect<number, never, never>
// ▼
const success = Effect.succeed(42)
succeed(array_: readonly OutElem[]array_[let index: numberindex++])
}
}
})
}
const const next: OutElemnext = let array: readonly OutElem[]array[let index: numberindex++]
if (let index: numberindex >= let array: readonly OutElem[]array.ReadonlyArray<T>.length: numberGets the length of the array. This is a number one higher than the highest element defined in an array.
length) {
let array: readonly OutElem[] | undefinedarray = var undefinedundefined
let index: numberindex = 0
}
return import EffectEffect.const succeed: <A>(value: A) => Effect<A>Creates an Effect that always succeeds with a given value.
When to use
Use when an effect should complete successfully with a specific value without any errors
or external dependencies.
Example (Creating a successful effect)
import { Effect } from "effect"
// Creating an effect that represents a successful scenario
//
// ┌─── Effect<number, never, never>
// ▼
const success = Effect.succeed(42)
succeed(const next: OutElemnext)
})
return import EffectEffect.const succeed: <A>(value: A) => Effect<A>Creates an Effect that always succeeds with a given value.
When to use
Use when an effect should complete successfully with a specific value without any errors
or external dependencies.
Example (Creating a successful effect)
import { Effect } from "effect"
// Creating an effect that represents a successful scenario
//
// ┌─── Effect<number, never, never>
// ▼
const success = Effect.succeed(42)
succeed(const pump: Effect.Effect<
OutElem,
OutErr | Cause.Done<OutDone>,
never
>
const pump: {
pipe: { <A>(this: A): A; <A, B = never>(this: A, ab: (_: A) => B): B; <A, B = never, C = never>(this: A, ab: (_: A) => B, bc: (_: B) => C): C; <A, B = never, C = never, D = never>(this: A, ab: (_: A) => B, bc: (_: B) => C, cd: (_: C) => D): D; <…;
toString: () => string;
toJSON: () => unknown;
}
Referenced by 12 symbols