<S, OutElem>(initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): <
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env
>(
self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>
) => Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>
<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, S>(
self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>,
initial: S,
f: (s: S, a: Types.NoInfer<OutElem>) => S
): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>Transforms a channel statefully by scanning over its output with an accumulator function. Emits the intermediate results of the scan operation.
Example (Scanning channel output)
import { Channel } from "effect"
// Create a channel with numbers
const numbersChannel = Channel.fromIterable([1, 2, 3, 4, 5])
// Scan to create running sum
const runningSumChannel = Channel.scan(numbersChannel, 0, (sum, n) => sum + n)
// Outputs: 0, 1, 3, 6, 10, 15
// Note: emits the initial value and each intermediate result
// Scan with string concatenation
const wordsChannel = Channel.fromIterable(["hello", "world", "from", "effect"])
const sentenceChannel = Channel.scan(
wordsChannel,
"",
(sentence, word) => sentence === "" ? word : `${sentence} ${word}`
)
// Outputs: "", "hello", "hello world", "hello world from", "hello world from effect"sequencing
Source effect/Channel.ts:372328 lines
export const const scan: {
<S, OutElem>(
initial: S,
f: (s: S, a: Types.NoInfer<OutElem>) => S
): <
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env
>(
self: Channel<
OutElem,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env
>
) => Channel<
S,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env
>
<
OutElem,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env,
S
>(
self: Channel<
OutElem,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env
>,
initial: S,
f: (s: S, a: Types.NoInfer<OutElem>) => S
): Channel<
S,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env
>
}
Transforms a channel statefully by scanning over its output with an accumulator function.
Emits the intermediate results of the scan operation.
Example (Scanning channel output)
import { Channel } from "effect"
// Create a channel with numbers
const numbersChannel = Channel.fromIterable([1, 2, 3, 4, 5])
// Scan to create running sum
const runningSumChannel = Channel.scan(numbersChannel, 0, (sum, n) => sum + n)
// Outputs: 0, 1, 3, 6, 10, 15
// Note: emits the initial value and each intermediate result
// Scan with string concatenation
const wordsChannel = Channel.fromIterable(["hello", "world", "from", "effect"])
const sentenceChannel = Channel.scan(
wordsChannel,
"",
(sentence, word) => sentence === "" ? word : `${sentence} ${word}`
)
// Outputs: "", "hello", "hello world", "hello world from", "hello world from effect"
scan: {
<function (type parameter) S in <S, OutElem>(initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): <OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>) => Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>S, function (type parameter) OutElem in <S, OutElem>(initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): <OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>) => Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>OutElem>(initial: Sinitial: function (type parameter) S in <S, OutElem>(initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): <OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>) => Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>S, f: (s: S, a: Types.NoInfer<OutElem>) => Sf: (s: Ss: function (type parameter) S in <S, OutElem>(initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): <OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>) => Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>S, a: Types.NoInfer<OutElem>a: import TypesTypes.type NoInfer<A> = [A][A extends any
? 0
: never]
Prevents TypeScript from inferring a type parameter from a specific
position.
When to use
Use when a function parameter must match an inferred type without becoming
an inference source.
Details
The parameter using NoInfer must still match the inferred type.
Example (Controlling inference)
import type { Types } from "effect"
declare function withDefault<T>(value: T, fallback: Types.NoInfer<T>): T
// T is inferred as "a" | "b" from the first argument only
const result = withDefault<"a" | "b">("a", "b")
NoInfer<function (type parameter) OutElem in <S, OutElem>(initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): <OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>) => Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>OutElem>) => function (type parameter) S in <S, OutElem>(initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): <OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>) => Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>S): <
function (type parameter) OutErr in <OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>OutErr,
function (type parameter) OutDone in <OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>OutDone,
function (type parameter) InElem in <OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>InElem,
function (type parameter) InErr in <OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>InErr,
function (type parameter) InDone in <OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>InDone,
function (type parameter) Env in <OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>Env
>(self: Channel<
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<function (type parameter) OutElem in <S, OutElem>(initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): <OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>) => Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>OutElem, function (type parameter) OutErr in <OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>OutErr, function (type parameter) OutDone in <OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>OutDone, function (type parameter) InElem in <OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>InElem, function (type parameter) InErr in <OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>InErr, function (type parameter) InDone in <OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>InDone, function (type parameter) Env in <OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<S, 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) S in <S, OutElem>(initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): <OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>) => Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>S,
function (type parameter) OutErr in <OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>OutErr,
function (type parameter) OutDone in <OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>OutDone,
function (type parameter) InElem in <OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>InElem,
function (type parameter) InErr in <OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>InErr,
function (type parameter) InDone in <OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>InDone,
function (type parameter) Env in <OutErr, OutDone, InElem, InErr, InDone, Env>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>Env
>
<function (type parameter) OutElem in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, S>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>OutElem, function (type parameter) OutErr in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, S>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>OutErr, function (type parameter) OutDone in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, S>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>OutDone, function (type parameter) InElem in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, S>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>InElem, function (type parameter) InErr in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, S>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>InErr, function (type parameter) InDone in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, S>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>InDone, function (type parameter) Env in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, S>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>Env, function (type parameter) S in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, S>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>S>(
self: Channel<
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<function (type parameter) OutElem in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, S>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>OutElem, function (type parameter) OutErr in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, S>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>OutErr, function (type parameter) OutDone in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, S>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>OutDone, function (type parameter) InElem in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, S>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>InElem, function (type parameter) InErr in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, S>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>InErr, function (type parameter) InDone in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, S>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>InDone, function (type parameter) Env in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, S>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>Env>,
initial: Sinitial: function (type parameter) S in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, S>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>S,
f: (s: S, a: Types.NoInfer<OutElem>) => Sf: (s: Ss: function (type parameter) S in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, S>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>S, a: Types.NoInfer<OutElem>a: import TypesTypes.type NoInfer<A> = [A][A extends any
? 0
: never]
Prevents TypeScript from inferring a type parameter from a specific
position.
When to use
Use when a function parameter must match an inferred type without becoming
an inference source.
Details
The parameter using NoInfer must still match the inferred type.
Example (Controlling inference)
import type { Types } from "effect"
declare function withDefault<T>(value: T, fallback: Types.NoInfer<T>): T
// T is inferred as "a" | "b" from the first argument only
const result = withDefault<"a" | "b">("a", "b")
NoInfer<function (type parameter) OutElem in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, S>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>OutElem>) => function (type parameter) S in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, S>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>S
): 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) S in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, S>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>S, function (type parameter) OutErr in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, S>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>OutErr, function (type parameter) OutDone in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, S>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>OutDone, function (type parameter) InElem in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, S>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>InElem, function (type parameter) InErr in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, S>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>InErr, function (type parameter) InDone in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, S>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>InDone, function (type parameter) Env in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, S>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>Env>
} = dual<(...args: Array<any>) => any, <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, S>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S) => Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>>(arity: 3, body: <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, S>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S) => Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>): ((...args: Array<any>) => any) & (<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, S>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S) => Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>) (+1 overload)Creates a function that can be called in data-first style or data-last
(pipe-friendly) style.
When to use
Use to expose one implementation through both direct and pipe-friendly
call styles.
Details
Pass either the arity of the uncurried function or a predicate that decides
whether the current call is data-first. Arity is the common case. Use a
predicate when optional arguments make arity ambiguous.
Example (Selecting data-first or data-last style by arity)
import { Function, pipe } from "effect"
const sum = Function.dual<
(that: number) => (self: number) => number,
(self: number, that: number) => number
>(2, (self, that) => self + that)
console.log(sum(2, 3)) // 5
console.log(pipe(2, sum(3))) // 5
Example (Defining overloads with call signatures)
import { Function, pipe } from "effect"
const sum: {
(that: number): (self: number) => number
(self: number, that: number): number
} = Function.dual(2, (self: number, that: number): number => self + that)
console.log(sum(2, 3)) // 5
console.log(pipe(2, sum(3))) // 5
Example (Selecting data-first or data-last style with a predicate)
import { Function, pipe } from "effect"
const sum = Function.dual<
(that: number) => (self: number) => number,
(self: number, that: number) => number
>(
(args) => args.length === 2,
(self, that) => self + that
)
console.log(sum(2, 3)) // 5
console.log(pipe(2, sum(3))) // 5
dual(3, <function (type parameter) OutElem in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, S>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>OutElem, function (type parameter) OutErr in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, S>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>OutErr, function (type parameter) OutDone in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, S>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>OutDone, function (type parameter) InElem in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, S>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>InElem, function (type parameter) InErr in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, S>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>InErr, function (type parameter) InDone in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, S>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>InDone, function (type parameter) Env in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, S>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>Env, function (type parameter) S in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, S>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>S>(
self: Channel<
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<function (type parameter) OutElem in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, S>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>OutElem, function (type parameter) OutErr in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, S>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>OutErr, function (type parameter) OutDone in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, S>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>OutDone, function (type parameter) InElem in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, S>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>InElem, function (type parameter) InErr in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, S>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>InErr, function (type parameter) InDone in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, S>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>InDone, function (type parameter) Env in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, S>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>Env>,
initial: Sinitial: function (type parameter) S in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, S>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>S,
f: (s: S, a: Types.NoInfer<OutElem>) => Sf: (s: Ss: function (type parameter) S in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, S>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>S, a: Types.NoInfer<OutElem>a: import TypesTypes.type NoInfer<A> = [A][A extends any
? 0
: never]
Prevents TypeScript from inferring a type parameter from a specific
position.
When to use
Use when a function parameter must match an inferred type without becoming
an inference source.
Details
The parameter using NoInfer must still match the inferred type.
Example (Controlling inference)
import type { Types } from "effect"
declare function withDefault<T>(value: T, fallback: Types.NoInfer<T>): T
// T is inferred as "a" | "b" from the first argument only
const result = withDefault<"a" | "b">("a", "b")
NoInfer<function (type parameter) OutElem in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, S>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>OutElem>) => function (type parameter) S in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, S>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>S
): 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) S in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, S>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>S, function (type parameter) OutErr in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, S>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>OutErr, function (type parameter) OutDone in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, S>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>OutDone, function (type parameter) InElem in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, S>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>InElem, function (type parameter) InErr in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, S>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>InErr, function (type parameter) InDone in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, S>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>InDone, function (type parameter) Env in <OutElem, OutErr, OutDone, InElem, InErr, InDone, Env, S>(self: Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env>, initial: S, f: (s: S, a: Types.NoInfer<OutElem>) => S): Channel<S, OutErr, OutDone, InElem, InErr, InDone, Env>Env> =>
const scanEffect: {
<S, OutElem, E, R>(
initial: S,
f: (
s: S,
a: Types.NoInfer<OutElem>
) => Effect.Effect<S, E, R>
): <
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env
>(
self: Channel<
OutElem,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env
>
) => Channel<
S,
OutErr | E,
OutDone,
InElem,
InErr,
InDone,
Env | R
>
<
OutElem,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env,
S,
E,
R
>(
self: Channel<
OutElem,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env
>,
initial: S,
f: (
s: S,
a: Types.NoInfer<OutElem>
) => Effect.Effect<S, E, R>
): Channel<
S,
OutErr | E,
OutDone,
InElem,
InErr,
InDone,
Env | R
>
}
self: Channel<
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; <…;
}
initial: Sinitial, (s: Ss, a: Types.NoInfer<OutElem>a) => 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(f: (s: S, a: Types.NoInfer<OutElem>) => Sf(s: Ss, a: Types.NoInfer<OutElem>a))))