<Output>(logger: Logger<unknown, Output>): <A, E, R>(
effect: Effect<A, E, R>
) => Effect<A, E, R>
<A, E, R, Output>(
effect: Effect<A, E, R>,
logger: Logger<unknown, Output>
): Effect<A, E, R>Adds a logger to the set of loggers which will output logs for this effect.
Example (Adding a logger to an effect)
import { Effect, Logger } from "effect"
// Create a custom logger that logs to the console
const customLogger = Logger.make(({ message }) =>
Effect.sync(() => console.log(`[CUSTOM]: ${message}`))
)
const program = Effect.gen(function*() {
yield* Effect.log("This will go to both default and custom logger")
return "completed"
})
// Add the custom logger to the effect
const programWithLogger = Effect.withLogger(program, customLogger)
Effect.runPromise(programWithLogger)
// Output includes both default and custom log outputsexport const const withLogger: (<Output>(
logger: Logger<unknown, Output>
) => <A, E, R>(
effect: Effect<A, E, R>
) => Effect<A, E, R>) &
(<A, E, R, Output>(
effect: Effect<A, E, R>,
logger: Logger<unknown, Output>
) => Effect<A, E, R>)
Adds a logger to the set of loggers which will output logs for this effect.
Example (Adding a logger to an effect)
import { Effect, Logger } from "effect"
// Create a custom logger that logs to the console
const customLogger = Logger.make(({ message }) =>
Effect.sync(() => console.log(`[CUSTOM]: ${message}`))
)
const program = Effect.gen(function*() {
yield* Effect.log("This will go to both default and custom logger")
return "completed"
})
// Add the custom logger to the effect
const programWithLogger = Effect.withLogger(program, customLogger)
Effect.runPromise(programWithLogger)
// Output includes both default and custom log outputs
withLogger = dual<<Output>(logger: Logger<unknown, Output>) => <A, E, R>(effect: Effect<A, E, R>) => Effect<A, E, R>, <A, E, R, Output>(effect: Effect<A, E, R>, logger: Logger<unknown, Output>) => Effect<A, E, R>>(arity: 2, body: <A, E, R, Output>(effect: Effect<A, E, R>, logger: Logger<unknown, Output>) => Effect<A, E, R>): (<Output>(logger: Logger<unknown, Output>) => <A, E, R>(effect: Effect<A, E, R>) => Effect<A, E, R>) & (<A, E, R, Output>(effect: Effect<A, E, R>, logger: Logger<unknown, Output>) => Effect<A, E, R>) (+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<
<function (type parameter) Output in <Output>(logger: Logger<unknown, Output>): <A, E, R>(effect: Effect<A, E, R>) => Effect<A, E, R>Output>(
logger: Logger<unknown, Output>(parameter) logger: {
log: (options: Options<unknown>) => Output;
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 Logger<in Message, out Output>A logger that transforms a runtime log event into an output value.
Details
The runtime calls log with the message, level, cause, fiber, and timestamp
for each log event. Use Logger.layer to install one or more loggers for an
effect.
Example (Creating custom loggers)
import { Effect, Logger } from "effect"
// Create a custom logger that accepts unknown messages and returns void
const stringLogger = Logger.make<unknown, void>((options) => {
console.log(`[${options.logLevel}] ${options.message}`)
})
// Create a logger that accepts any message type and returns a formatted string
const formattedLogger = Logger.make<unknown, string>((options) =>
`${options.date.toISOString()} [${options.logLevel}] ${options.message}`
)
// Use the logger in an Effect program
const program = Effect.log("Hello World").pipe(
Effect.provide(Logger.layer([stringLogger]))
)
Logger<unknown, function (type parameter) Output in <Output>(logger: Logger<unknown, Output>): <A, E, R>(effect: Effect<A, E, R>) => Effect<A, E, R>Output>
) => <function (type parameter) A in <A, E, R>(effect: Effect<A, E, R>): Effect<A, E, R>A, function (type parameter) E in <A, E, R>(effect: Effect<A, E, R>): Effect<A, E, R>E, function (type parameter) R in <A, E, R>(effect: Effect<A, E, R>): Effect<A, E, R>R>(effect: Effect<A, E, R>(parameter) effect: {
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;
}
interface Effect<out A, out E = never, out R = never>The Effect interface defines a value that lazily describes a workflow or
job. The workflow requires some context R, and may fail with an error of
type E, or succeed with a value of type A.
When to use
Use when you need to represent a lazy, composable workflow that can require
services, fail with a typed error, or succeed with a typed value.
Details
Effect values model resourceful interaction with the outside world,
including synchronous, asynchronous, concurrent, and parallel interaction.
They use a fiber-based concurrency model, with built-in support for
scheduling, fine-grained interruption, structured concurrency, and high
scalability.
To run an Effect value, you need a Runtime, which is a type that is
capable of executing Effect values.
Effect<function (type parameter) A in <A, E, R>(effect: Effect<A, E, R>): Effect<A, E, R>A, function (type parameter) E in <A, E, R>(effect: Effect<A, E, R>): Effect<A, E, R>E, function (type parameter) R in <A, E, R>(effect: Effect<A, E, R>): Effect<A, E, R>R>) => interface Effect<out A, out E = never, out R = never>The Effect interface defines a value that lazily describes a workflow or
job. The workflow requires some context R, and may fail with an error of
type E, or succeed with a value of type A.
When to use
Use when you need to represent a lazy, composable workflow that can require
services, fail with a typed error, or succeed with a typed value.
Details
Effect values model resourceful interaction with the outside world,
including synchronous, asynchronous, concurrent, and parallel interaction.
They use a fiber-based concurrency model, with built-in support for
scheduling, fine-grained interruption, structured concurrency, and high
scalability.
To run an Effect value, you need a Runtime, which is a type that is
capable of executing Effect values.
Effect<function (type parameter) A in <A, E, R>(effect: Effect<A, E, R>): Effect<A, E, R>A, function (type parameter) E in <A, E, R>(effect: Effect<A, E, R>): Effect<A, E, R>E, function (type parameter) R in <A, E, R>(effect: Effect<A, E, R>): Effect<A, E, R>R>,
<function (type parameter) A in <A, E, R, Output>(effect: Effect<A, E, R>, logger: Logger<unknown, Output>): Effect<A, E, R>A, function (type parameter) E in <A, E, R, Output>(effect: Effect<A, E, R>, logger: Logger<unknown, Output>): Effect<A, E, R>E, function (type parameter) R in <A, E, R, Output>(effect: Effect<A, E, R>, logger: Logger<unknown, Output>): Effect<A, E, R>R, function (type parameter) Output in <A, E, R, Output>(effect: Effect<A, E, R>, logger: Logger<unknown, Output>): Effect<A, E, R>Output>(
effect: Effect<A, E, R>(parameter) effect: {
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;
}
interface Effect<out A, out E = never, out R = never>The Effect interface defines a value that lazily describes a workflow or
job. The workflow requires some context R, and may fail with an error of
type E, or succeed with a value of type A.
When to use
Use when you need to represent a lazy, composable workflow that can require
services, fail with a typed error, or succeed with a typed value.
Details
Effect values model resourceful interaction with the outside world,
including synchronous, asynchronous, concurrent, and parallel interaction.
They use a fiber-based concurrency model, with built-in support for
scheduling, fine-grained interruption, structured concurrency, and high
scalability.
To run an Effect value, you need a Runtime, which is a type that is
capable of executing Effect values.
Effect<function (type parameter) A in <A, E, R, Output>(effect: Effect<A, E, R>, logger: Logger<unknown, Output>): Effect<A, E, R>A, function (type parameter) E in <A, E, R, Output>(effect: Effect<A, E, R>, logger: Logger<unknown, Output>): Effect<A, E, R>E, function (type parameter) R in <A, E, R, Output>(effect: Effect<A, E, R>, logger: Logger<unknown, Output>): Effect<A, E, R>R>,
logger: Logger<unknown, Output>(parameter) logger: {
log: (options: Options<unknown>) => Output;
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 Logger<in Message, out Output>A logger that transforms a runtime log event into an output value.
Details
The runtime calls log with the message, level, cause, fiber, and timestamp
for each log event. Use Logger.layer to install one or more loggers for an
effect.
Example (Creating custom loggers)
import { Effect, Logger } from "effect"
// Create a custom logger that accepts unknown messages and returns void
const stringLogger = Logger.make<unknown, void>((options) => {
console.log(`[${options.logLevel}] ${options.message}`)
})
// Create a logger that accepts any message type and returns a formatted string
const formattedLogger = Logger.make<unknown, string>((options) =>
`${options.date.toISOString()} [${options.logLevel}] ${options.message}`
)
// Use the logger in an Effect program
const program = Effect.log("Hello World").pipe(
Effect.provide(Logger.layer([stringLogger]))
)
Logger<unknown, function (type parameter) Output in <A, E, R, Output>(effect: Effect<A, E, R>, logger: Logger<unknown, Output>): Effect<A, E, R>Output>
) => interface Effect<out A, out E = never, out R = never>The Effect interface defines a value that lazily describes a workflow or
job. The workflow requires some context R, and may fail with an error of
type E, or succeed with a value of type A.
When to use
Use when you need to represent a lazy, composable workflow that can require
services, fail with a typed error, or succeed with a typed value.
Details
Effect values model resourceful interaction with the outside world,
including synchronous, asynchronous, concurrent, and parallel interaction.
They use a fiber-based concurrency model, with built-in support for
scheduling, fine-grained interruption, structured concurrency, and high
scalability.
To run an Effect value, you need a Runtime, which is a type that is
capable of executing Effect values.
Effect<function (type parameter) A in <A, E, R, Output>(effect: Effect<A, E, R>, logger: Logger<unknown, Output>): Effect<A, E, R>A, function (type parameter) E in <A, E, R, Output>(effect: Effect<A, E, R>, logger: Logger<unknown, Output>): Effect<A, E, R>E, function (type parameter) R in <A, E, R, Output>(effect: Effect<A, E, R>, logger: Logger<unknown, Output>): Effect<A, E, R>R>
>(2, (effect: Effect<A, E, R>(parameter) effect: {
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;
}
logger: Logger<unknown, Output>(parameter) logger: {
log: (options: Options<unknown>) => Output;
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; <…;
}
import internalinternal.const updateService: {
<I, A>(
service: Context.Key<I, A>,
f: (value: A) => A
): <XA, E, R>(
self: Effect.Effect<XA, E, R>
) => Effect.Effect<XA, E, R | I>
<XA, E, R, I, A>(
self: Effect.Effect<XA, E, R>,
service: Context.Key<I, A>,
f: (value: A) => A
): Effect.Effect<XA, E, R | I>
}
effect: Effect<A, E, R>(parameter) effect: {
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 internalinternal.const CurrentLoggers: Context.Reference<
ReadonlySet<Logger<unknown, any>>
>
const CurrentLoggers: {
key: string;
Service: {
forEach: (callbackfn: (value: Logger<unknown, any>, value2: Logger<unknown, any>, set: ReadonlySet<Logger<unknown, any>>) => void, thisArg?: any) => void;
has: (value: Logger<unknown, any>) => boolean;
size: number;
entries: () => SetIterator<[Logger<unknown, any>, Logger<unknown, any>]>;
keys: () => SetIterator<Logger<unknown, any>>;
values: () => SetIterator<Logger<unknown, any>>;
union: (other: ReadonlySetLike<U>) => Set<Logger<unknown, any> | U>;
intersection: (other: ReadonlySetLike<U>) => Set<Logger<unknown, any> & U>;
difference: (other: ReadonlySetLike<U>) => Set<Logger<unknown, any>>;
symmetricDifference: (other: ReadonlySetLike<U>) => Set<Logger<unknown, any> | U>;
isSubsetOf: (other: ReadonlySetLike<unknown>) => boolean;
isSupersetOf: (other: ReadonlySetLike<unknown>) => boolean;
isDisjointFrom: (other: ReadonlySetLike<unknown>) => boolean;
};
defaultValue: () => Shape;
of: (this: void, self: ReadonlySet<Logger<unknown, any>>) => ReadonlySet<Logger<unknown, any>>;
context: (self: ReadonlySet<Logger<unknown, any>>) => Context.Context<never>;
use: (f: (service: ReadonlySet<Logger<unknown, any>>) => Effect<A, E, R>) => Effect<A, E, R>;
useSync: (f: (service: ReadonlySet<Logger<unknown, any>>) => A) => Effect<A, never, never>;
Identifier: Identifier;
stack: string | undefined;
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;
}
loggers: ReadonlySet<Logger<unknown, any>>loggers) => new var Set: SetConstructor
new <any>(iterable?: Iterable<any> | null | undefined) => Set<any> (+1 overload)
loggers: ReadonlySet<Logger<unknown, any>>loggers, logger: Logger<unknown, Output>(parameter) logger: {
log: (options: Options<unknown>) => Output;
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; <…;
}