<Env, OutElem, OutErr, OutDone, InElem, InErr, InDone, Env2>(
f: (
context: Context.Context<Env>
) => Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env2>
): Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env | Env2>Creates a channel from the specified services.
services
Source effect/Channel.ts:71766 lines
export const const contextWith: <
Env,
OutElem,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env2
>(
f: (
context: Context.Context<Env>
) => Channel<
OutElem,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env2
>
) => Channel<
OutElem,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env | Env2
>
Creates a channel from the specified services.
contextWith = <function (type parameter) Env in <Env, OutElem, OutErr, OutDone, InElem, InErr, InDone, Env2>(f: (context: Context.Context<Env>) => Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env2>): Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env | Env2>Env, function (type parameter) OutElem in <Env, OutElem, OutErr, OutDone, InElem, InErr, InDone, Env2>(f: (context: Context.Context<Env>) => Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env2>): Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env | Env2>OutElem, function (type parameter) OutErr in <Env, OutElem, OutErr, OutDone, InElem, InErr, InDone, Env2>(f: (context: Context.Context<Env>) => Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env2>): Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env | Env2>OutErr, function (type parameter) OutDone in <Env, OutElem, OutErr, OutDone, InElem, InErr, InDone, Env2>(f: (context: Context.Context<Env>) => Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env2>): Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env | Env2>OutDone, function (type parameter) InElem in <Env, OutElem, OutErr, OutDone, InElem, InErr, InDone, Env2>(f: (context: Context.Context<Env>) => Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env2>): Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env | Env2>InElem, function (type parameter) InErr in <Env, OutElem, OutErr, OutDone, InElem, InErr, InDone, Env2>(f: (context: Context.Context<Env>) => Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env2>): Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env | Env2>InErr, function (type parameter) InDone in <Env, OutElem, OutErr, OutDone, InElem, InErr, InDone, Env2>(f: (context: Context.Context<Env>) => Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env2>): Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env | Env2>InDone, function (type parameter) Env2 in <Env, OutElem, OutErr, OutDone, InElem, InErr, InDone, Env2>(f: (context: Context.Context<Env>) => Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env2>): Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env | Env2>Env2>(
f: (
context: Context.Context<Env>
) => Channel<
OutElem,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env2
>
context: Context.Context<Env>(parameter) context: {
mapUnsafe: ReadonlyMap<string, any>;
mutable: boolean;
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 ContextContext.interface Context<in Services>Immutable collection of service implementations used for dependency
injection in Effect programs.
Details
The type parameter tracks the service identifiers available in the context.
At runtime, services are stored by each key's string key.
Example (Creating a context with multiple services)
import { Context } from "effect"
// Create a context with multiple services
const Logger = Context.Service<{ log: (msg: string) => void }>("Logger")
const Database = Context.Service<{ query: (sql: string) => string }>(
"Database"
)
const context = Context.make(Logger, {
log: (msg: string) => console.log(msg)
})
.pipe(Context.add(Database, { query: (sql) => `Result: ${sql}` }))
Context<function (type parameter) Env in <Env, OutElem, OutErr, OutDone, InElem, InErr, InDone, Env2>(f: (context: Context.Context<Env>) => Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env2>): Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env | Env2>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 <Env, OutElem, OutErr, OutDone, InElem, InErr, InDone, Env2>(f: (context: Context.Context<Env>) => Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env2>): Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env | Env2>OutElem, function (type parameter) OutErr in <Env, OutElem, OutErr, OutDone, InElem, InErr, InDone, Env2>(f: (context: Context.Context<Env>) => Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env2>): Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env | Env2>OutErr, function (type parameter) OutDone in <Env, OutElem, OutErr, OutDone, InElem, InErr, InDone, Env2>(f: (context: Context.Context<Env>) => Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env2>): Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env | Env2>OutDone, function (type parameter) InElem in <Env, OutElem, OutErr, OutDone, InElem, InErr, InDone, Env2>(f: (context: Context.Context<Env>) => Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env2>): Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env | Env2>InElem, function (type parameter) InErr in <Env, OutElem, OutErr, OutDone, InElem, InErr, InDone, Env2>(f: (context: Context.Context<Env>) => Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env2>): Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env | Env2>InErr, function (type parameter) InDone in <Env, OutElem, OutErr, OutDone, InElem, InErr, InDone, Env2>(f: (context: Context.Context<Env>) => Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env2>): Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env | Env2>InDone, function (type parameter) Env2 in <Env, OutElem, OutErr, OutDone, InElem, InErr, InDone, Env2>(f: (context: Context.Context<Env>) => Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env2>): Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env | Env2>Env2>
): 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 <Env, OutElem, OutErr, OutDone, InElem, InErr, InDone, Env2>(f: (context: Context.Context<Env>) => Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env2>): Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env | Env2>OutElem, function (type parameter) OutErr in <Env, OutElem, OutErr, OutDone, InElem, InErr, InDone, Env2>(f: (context: Context.Context<Env>) => Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env2>): Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env | Env2>OutErr, function (type parameter) OutDone in <Env, OutElem, OutErr, OutDone, InElem, InErr, InDone, Env2>(f: (context: Context.Context<Env>) => Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env2>): Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env | Env2>OutDone, function (type parameter) InElem in <Env, OutElem, OutErr, OutDone, InElem, InErr, InDone, Env2>(f: (context: Context.Context<Env>) => Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env2>): Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env | Env2>InElem, function (type parameter) InErr in <Env, OutElem, OutErr, OutDone, InElem, InErr, InDone, Env2>(f: (context: Context.Context<Env>) => Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env2>): Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env | Env2>InErr, function (type parameter) InDone in <Env, OutElem, OutErr, OutDone, InElem, InErr, InDone, Env2>(f: (context: Context.Context<Env>) => Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env2>): Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env | Env2>InDone, function (type parameter) Env in <Env, OutElem, OutErr, OutDone, InElem, InErr, InDone, Env2>(f: (context: Context.Context<Env>) => Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env2>): Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env | Env2>Env | function (type parameter) Env2 in <Env, OutElem, OutErr, OutDone, InElem, InErr, InDone, Env2>(f: (context: Context.Context<Env>) => Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env2>): Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env | Env2>Env2> =>
const fromTransform: <
OutElem,
OutErr,
OutDone,
InElem,
InErr,
InDone,
EX,
EnvX,
Env
>(
transform: (
upstream: Pull.Pull<InElem, InErr, InDone>,
scope: Scope.Scope
) => Effect.Effect<
Pull.Pull<OutElem, OutErr, OutDone, EnvX>,
EX,
Env
>
) => Channel<
OutElem,
Pull.ExcludeDone<OutErr> | EX,
OutDone,
InElem,
InErr,
InDone,
Env | EnvX
>
Creates a Channel from a transformation function that operates on upstream pulls.
Example (Creating channels from transforms)
import { Channel, Effect } from "effect"
const channel = Channel.fromTransform((upstream, scope) =>
Effect.succeed(upstream)
)
fromTransform((upstream: Pull.Pull<InElem, InErr, InDone, never>(parameter) upstream: {
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;
}
scope: Scope.Scope(parameter) scope: {
strategy: "sequential" | "parallel";
state: State.Open | State.Closed | State.Empty;
}
import EffectEffect.const contextWith: <R, A, E, R2>(
f: (
context: Context.Context<R>
) => Effect<A, E, R2>
) => Effect<A, E, R | R2>
Transforms the current context using the provided function.
When to use
Use to derive an effect from the complete Context.
Details
This function allows you to access the complete context and perform
computations based on all available services. This is useful when you need
to conditionally execute logic based on what services are available.
Example (Deriving values from the context)
import { Console, Context, Effect, Option } from "effect"
const Logger = Context.Service<{
log: (msg: string) => void
}>("Logger")
const Cache = Context.Service<{
get: (key: string) => string | null
}>("Cache")
const program = Effect.contextWith((services) => {
const cacheOption = Context.getOption(services, Cache)
const hasCache = Option.isSome(cacheOption)
if (hasCache) {
return Effect.gen(function*() {
const cache = yield* Effect.service(Cache)
yield* Console.log("Using cached data")
return cache.get("user:123") || "default"
})
} else {
return Effect.gen(function*() {
yield* Console.log("No cache available, using fallback")
return "fallback data"
})
}
})
const withCache = Effect.provideService(program, Cache, {
get: () => "cached_value"
})
contextWith((context: Context.Context<Env>(parameter) context: {
mapUnsafe: ReadonlyMap<string, any>;
mutable: boolean;
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 ContextContext.interface Context<in Services>Immutable collection of service implementations used for dependency
injection in Effect programs.
Details
The type parameter tracks the service identifiers available in the context.
At runtime, services are stored by each key's string key.
Example (Creating a context with multiple services)
import { Context } from "effect"
// Create a context with multiple services
const Logger = Context.Service<{ log: (msg: string) => void }>("Logger")
const Database = Context.Service<{ query: (sql: string) => string }>(
"Database"
)
const context = Context.make(Logger, {
log: (msg: string) => console.log(msg)
})
.pipe(Context.add(Database, { query: (sql) => `Result: ${sql}` }))
Context<function (type parameter) Env in <Env, OutElem, OutErr, OutDone, InElem, InErr, InDone, Env2>(f: (context: Context.Context<Env>) => Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env2>): Channel<OutElem, OutErr, OutDone, InElem, InErr, InDone, Env | Env2>Env>) => const toTransform: <
OutElem,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env
>(
channel: Channel<
OutElem,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env
>
) => (
upstream: Pull.Pull<InElem, InErr, InDone>,
scope: Scope.Scope
) => Effect.Effect<
Pull.Pull<OutElem, OutErr, OutDone>,
never,
Env
>
Converts a Channel back to its underlying transformation function.
Example (Extracting channel transforms)
import { Channel } from "effect"
const channel = Channel.succeed(42)
const transform = Channel.toTransform(channel)
// transform can now be used directly
toTransform(f: (
context: Context.Context<Env>
) => Channel<
OutElem,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env2
>
context: Context.Context<Env>(parameter) context: {
mapUnsafe: ReadonlyMap<string, any>;
mutable: boolean;
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;
}
upstream: Pull.Pull<InElem, InErr, InDone, never>(parameter) upstream: {
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;
}
scope: Scope.Scope(parameter) scope: {
strategy: "sequential" | "parallel";
state: State.Open | State.Closed | State.Empty;
}