<E2 = never, R2 = never>(condition: Effect<boolean, E2, R2>): <A, E, R>(
self: Effect<A, E, R>
) => Effect<Option<A>, E | E2, R | R2>
<A, E, R, E2 = never, R2 = never>(
self: Effect<A, E, R>,
condition: Effect<boolean, E2, R2>
): Effect<Option<A>, E | E2, R | R2>Runs an effect conditionally based on the result of an effectful boolean condition.
When to use
Use when you need an effectful check to decide whether another effect should run while representing the skipped case explicitly.
Details
The condition effect is evaluated first. If it succeeds with true, the
source effect is run and its success value is wrapped in Option.some. If it
succeeds with false, the source effect is skipped and the result is
Option.none. If the condition effect fails, that failure is preserved.
Example (Conditionally running an effect)
import { Console, Effect } from "effect"
const shouldLog = true
const program = Effect.when(
Console.log("Condition is true!"),
Effect.succeed(shouldLog)
)
Effect.runPromise(program).then(console.log)
// Output: "Condition is true!"
// { _id: 'Option', _tag: 'Some', value: undefined }export const const when: {
<E2 = never, R2 = never>(
condition: Effect<boolean, E2, R2>
): <A, E, R>(
self: Effect<A, E, R>
) => Effect<Option<A>, E | E2, R | R2>
<A, E, R, E2 = never, R2 = never>(
self: Effect<A, E, R>,
condition: Effect<boolean, E2, R2>
): Effect<Option<A>, E | E2, R | R2>
}
Runs an effect conditionally based on the result of an effectful boolean
condition.
When to use
Use when you need an effectful check to decide whether another effect should
run while representing the skipped case explicitly.
Details
The condition effect is evaluated first. If it succeeds with true, the
source effect is run and its success value is wrapped in Option.some. If it
succeeds with false, the source effect is skipped and the result is
Option.none. If the condition effect fails, that failure is preserved.
Example (Conditionally running an effect)
import { Console, Effect } from "effect"
const shouldLog = true
const program = Effect.when(
Console.log("Condition is true!"),
Effect.succeed(shouldLog)
)
Effect.runPromise(program).then(console.log)
// Output: "Condition is true!"
// { _id: 'Option', _tag: 'Some', value: undefined }
when: {
<function (type parameter) E2 in <E2 = never, R2 = never>(condition: Effect<boolean, E2, R2>): <A, E, R>(self: Effect<A, E, R>) => Effect<Option<A>, E | E2, R | R2>E2 = never, function (type parameter) R2 in <E2 = never, R2 = never>(condition: Effect<boolean, E2, R2>): <A, E, R>(self: Effect<A, E, R>) => Effect<Option<A>, E | E2, R | R2>R2 = never>(
condition: Effect<boolean, E2, R2>(parameter) condition: {
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<boolean, function (type parameter) E2 in <E2 = never, R2 = never>(condition: Effect<boolean, E2, R2>): <A, E, R>(self: Effect<A, E, R>) => Effect<Option<A>, E | E2, R | R2>E2, function (type parameter) R2 in <E2 = never, R2 = never>(condition: Effect<boolean, E2, R2>): <A, E, R>(self: Effect<A, E, R>) => Effect<Option<A>, E | E2, R | R2>R2>
): <function (type parameter) A in <A, E, R>(self: Effect<A, E, R>): Effect<Option<A>, E | E2, R | R2>A, function (type parameter) E in <A, E, R>(self: Effect<A, E, R>): Effect<Option<A>, E | E2, R | R2>E, function (type parameter) R in <A, E, R>(self: Effect<A, E, R>): Effect<Option<A>, E | E2, R | R2>R>(self: Effect<A, E, R>(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; <…;
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>(self: Effect<A, E, R>): Effect<Option<A>, E | E2, R | R2>A, function (type parameter) E in <A, E, R>(self: Effect<A, E, R>): Effect<Option<A>, E | E2, R | R2>E, function (type parameter) R in <A, E, R>(self: Effect<A, E, R>): Effect<Option<A>, E | E2, R | R2>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<type Option<A> = None<A> | Some<A>The Option data type represents optional values. An Option<A> is either
Some<A>, containing a value of type A, or None, representing absence.
When to use
Use to represent initial values that may not yet exist
- Returning from partial functions (not defined for all inputs)
- Managing optional fields in data structures
Namespace containing utility types for Option.
When to use
Use to access type-level helpers associated with Option.
Option<function (type parameter) A in <A, E, R>(self: Effect<A, E, R>): Effect<Option<A>, E | E2, R | R2>A>, function (type parameter) E in <A, E, R>(self: Effect<A, E, R>): Effect<Option<A>, E | E2, R | R2>E | function (type parameter) E2 in <E2 = never, R2 = never>(condition: Effect<boolean, E2, R2>): <A, E, R>(self: Effect<A, E, R>) => Effect<Option<A>, E | E2, R | R2>E2, function (type parameter) R in <A, E, R>(self: Effect<A, E, R>): Effect<Option<A>, E | E2, R | R2>R | function (type parameter) R2 in <E2 = never, R2 = never>(condition: Effect<boolean, E2, R2>): <A, E, R>(self: Effect<A, E, R>) => Effect<Option<A>, E | E2, R | R2>R2>
<function (type parameter) A in <A, E, R, E2 = never, R2 = never>(self: Effect<A, E, R>, condition: Effect<boolean, E2, R2>): Effect<Option<A>, E | E2, R | R2>A, function (type parameter) E in <A, E, R, E2 = never, R2 = never>(self: Effect<A, E, R>, condition: Effect<boolean, E2, R2>): Effect<Option<A>, E | E2, R | R2>E, function (type parameter) R in <A, E, R, E2 = never, R2 = never>(self: Effect<A, E, R>, condition: Effect<boolean, E2, R2>): Effect<Option<A>, E | E2, R | R2>R, function (type parameter) E2 in <A, E, R, E2 = never, R2 = never>(self: Effect<A, E, R>, condition: Effect<boolean, E2, R2>): Effect<Option<A>, E | E2, R | R2>E2 = never, function (type parameter) R2 in <A, E, R, E2 = never, R2 = never>(self: Effect<A, E, R>, condition: Effect<boolean, E2, R2>): Effect<Option<A>, E | E2, R | R2>R2 = never>(
self: Effect<A, E, R>(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; <…;
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, E2 = never, R2 = never>(self: Effect<A, E, R>, condition: Effect<boolean, E2, R2>): Effect<Option<A>, E | E2, R | R2>A, function (type parameter) E in <A, E, R, E2 = never, R2 = never>(self: Effect<A, E, R>, condition: Effect<boolean, E2, R2>): Effect<Option<A>, E | E2, R | R2>E, function (type parameter) R in <A, E, R, E2 = never, R2 = never>(self: Effect<A, E, R>, condition: Effect<boolean, E2, R2>): Effect<Option<A>, E | E2, R | R2>R>,
condition: Effect<boolean, E2, R2>(parameter) condition: {
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<boolean, function (type parameter) E2 in <A, E, R, E2 = never, R2 = never>(self: Effect<A, E, R>, condition: Effect<boolean, E2, R2>): Effect<Option<A>, E | E2, R | R2>E2, function (type parameter) R2 in <A, E, R, E2 = never, R2 = never>(self: Effect<A, E, R>, condition: Effect<boolean, E2, R2>): Effect<Option<A>, E | E2, R | R2>R2>
): 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<type Option<A> = None<A> | Some<A>The Option data type represents optional values. An Option<A> is either
Some<A>, containing a value of type A, or None, representing absence.
When to use
Use to represent initial values that may not yet exist
- Returning from partial functions (not defined for all inputs)
- Managing optional fields in data structures
Namespace containing utility types for Option.
When to use
Use to access type-level helpers associated with Option.
Option<function (type parameter) A in <A, E, R, E2 = never, R2 = never>(self: Effect<A, E, R>, condition: Effect<boolean, E2, R2>): Effect<Option<A>, E | E2, R | R2>A>, function (type parameter) E in <A, E, R, E2 = never, R2 = never>(self: Effect<A, E, R>, condition: Effect<boolean, E2, R2>): Effect<Option<A>, E | E2, R | R2>E | function (type parameter) E2 in <A, E, R, E2 = never, R2 = never>(self: Effect<A, E, R>, condition: Effect<boolean, E2, R2>): Effect<Option<A>, E | E2, R | R2>E2, function (type parameter) R in <A, E, R, E2 = never, R2 = never>(self: Effect<A, E, R>, condition: Effect<boolean, E2, R2>): Effect<Option<A>, E | E2, R | R2>R | function (type parameter) R2 in <A, E, R, E2 = never, R2 = never>(self: Effect<A, E, R>, condition: Effect<boolean, E2, R2>): Effect<Option<A>, E | E2, R | R2>R2>
} = import internalinternal.const when: {
<E2 = never, R2 = never>(
condition: Effect.Effect<boolean, E2, R2>
): <A, E, R>(
self: Effect.Effect<A, E, R>
) => Effect.Effect<
Option.Option<A>,
E | E2,
R | R2
>
<A, E, R, E2 = never, R2 = never>(
self: Effect.Effect<A, E, R>,
condition: Effect.Effect<boolean, E2, R2>
): Effect.Effect<
Option.Option<A>,
E | E2,
R | R2
>
}