<E, B, E2, R2>(
predicate: Predicate.Predicate<Cause.Cause<E>>,
f: (cause: Cause.Cause<E>) => Effect<B, E2, R2>
): <A, R>(self: Effect<A, E, R>) => Effect<A | B, E | E2, R | R2>
<A, E, R, B, E2, R2>(
self: Effect<A, E, R>,
predicate: Predicate.Predicate<Cause.Cause<E>>,
f: (cause: Cause.Cause<E>) => Effect<B, E2, R2>
): Effect<A | B, E | E2, R | R2>Recovers from specific failures based on a predicate.
When to use
Use to recover an Effect from full causes selected by a predicate.
Details
This function allows you to conditionally catch and recover from failures that match a specific predicate. This is useful when you want to handle only certain types of errors while letting others propagate.
Example (Recovering from selected causes)
import { Cause, Console, Effect } from "effect"
const httpRequest = Effect.fail("Network Error")
// Only catch network-related failures
const program = Effect.catchCauseIf(
httpRequest,
Cause.hasFails,
(cause) =>
Effect.gen(function*() {
yield* Console.log(`Caught network error: ${Cause.squash(cause)}`)
return "Fallback response"
})
)
Effect.runPromise(program).then(console.log)
// Output: "Caught network error: Network Error"
// Then: "Fallback response"export const const catchCauseIf: {
<E, B, E2, R2>(
predicate: Predicate.Predicate<
Cause.Cause<E>
>,
f: (
cause: Cause.Cause<E>
) => Effect<B, E2, R2>
): <A, R>(
self: Effect<A, E, R>
) => Effect<A | B, E | E2, R | R2>
<A, E, R, B, E2, R2>(
self: Effect<A, E, R>,
predicate: Predicate.Predicate<
Cause.Cause<E>
>,
f: (
cause: Cause.Cause<E>
) => Effect<B, E2, R2>
): Effect<A | B, E | E2, R | R2>
}
Recovers from specific failures based on a predicate.
When to use
Use to recover an Effect from full causes selected by a predicate.
Details
This function allows you to conditionally catch and recover from failures
that match a specific predicate. This is useful when you want to handle
only certain types of errors while letting others propagate.
Example (Recovering from selected causes)
import { Cause, Console, Effect } from "effect"
const httpRequest = Effect.fail("Network Error")
// Only catch network-related failures
const program = Effect.catchCauseIf(
httpRequest,
Cause.hasFails,
(cause) =>
Effect.gen(function*() {
yield* Console.log(`Caught network error: ${Cause.squash(cause)}`)
return "Fallback response"
})
)
Effect.runPromise(program).then(console.log)
// Output: "Caught network error: Network Error"
// Then: "Fallback response"
catchCauseIf: {
<function (type parameter) E in <E, B, E2, R2>(predicate: Predicate.Predicate<Cause.Cause<E>>, f: (cause: Cause.Cause<E>) => Effect<B, E2, R2>): <A, R>(self: Effect<A, E, R>) => Effect<A | B, E | E2, R | R2>E, function (type parameter) B in <E, B, E2, R2>(predicate: Predicate.Predicate<Cause.Cause<E>>, f: (cause: Cause.Cause<E>) => Effect<B, E2, R2>): <A, R>(self: Effect<A, E, R>) => Effect<A | B, E | E2, R | R2>B, function (type parameter) E2 in <E, B, E2, R2>(predicate: Predicate.Predicate<Cause.Cause<E>>, f: (cause: Cause.Cause<E>) => Effect<B, E2, R2>): <A, R>(self: Effect<A, E, R>) => Effect<A | B, E | E2, R | R2>E2, function (type parameter) R2 in <E, B, E2, R2>(predicate: Predicate.Predicate<Cause.Cause<E>>, f: (cause: Cause.Cause<E>) => Effect<B, E2, R2>): <A, R>(self: Effect<A, E, R>) => Effect<A | B, E | E2, R | R2>R2>(
predicate: Predicate.Predicate<Cause.Cause<E>>predicate: import PredicatePredicate.interface Predicate<in A>A function that decides whether a value of type A satisfies a condition.
When to use
Use when you want a reusable boolean check for A, especially when you plan
to combine checks with
and
/
or
or pass a predicate to arrays
and iterables.
Details
A predicate returns true or false and never throws by itself. It does not
narrow types unless you use Refinement.
Example (Defining a predicate)
import { Predicate } from "effect"
const isPositive: Predicate.Predicate<number> = (n) => n > 0
console.log(isPositive(1))
Type-level utilities for working with
Predicate
types.
When to use
Use when you need to extract input types from predicate signatures while
writing generic helpers over predicate types.
Details
These utilities are type-only, create no runtime values, and the namespace is
erased at runtime.
Example (Extracting predicate input)
import { Predicate } from "effect"
type IsString = Predicate.Predicate<string>
type Input = Predicate.Predicate.In<IsString>
Predicate<import CauseCause.interface Cause<out E>A structured representation of how an Effect failed.
When to use
Use to preserve the full structured failure information for an effect instead
of collapsing it to a single error value.
Details
Access the individual failure entries through the reasons array, then
narrow each entry with
isFailReason
,
isDieReason
, or
- Use
hasFails
/
hasDies
/
hasInterrupts
to test
for the presence of specific reason kinds without iterating.
- Use
findError
/
findDefect
to extract the first value
of a given kind.
- Use
combine
to merge two causes.
Cause implements Equal — two causes with the same reasons (by value)
compare as equal.
Example (Creating and inspecting a cause)
import { Cause } from "effect"
const cause = Cause.fail("Something went wrong")
console.log(cause.reasons.length) // 1
console.log(Cause.isFailReason(cause.reasons[0])) // true
Companion namespace for the Cause interface.
Cause<function (type parameter) E in <E, B, E2, R2>(predicate: Predicate.Predicate<Cause.Cause<E>>, f: (cause: Cause.Cause<E>) => Effect<B, E2, R2>): <A, R>(self: Effect<A, E, R>) => Effect<A | B, E | E2, R | R2>E>>,
f: (
cause: Cause.Cause<E>
) => Effect<B, E2, R2>
cause: Cause.Cause<E>(parameter) cause: {
reasons: ReadonlyArray<Reason<E>>;
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 CauseCause.interface Cause<out E>A structured representation of how an Effect failed.
When to use
Use to preserve the full structured failure information for an effect instead
of collapsing it to a single error value.
Details
Access the individual failure entries through the reasons array, then
narrow each entry with
isFailReason
,
isDieReason
, or
- Use
hasFails
/
hasDies
/
hasInterrupts
to test
for the presence of specific reason kinds without iterating.
- Use
findError
/
findDefect
to extract the first value
of a given kind.
- Use
combine
to merge two causes.
Cause implements Equal — two causes with the same reasons (by value)
compare as equal.
Example (Creating and inspecting a cause)
import { Cause } from "effect"
const cause = Cause.fail("Something went wrong")
console.log(cause.reasons.length) // 1
console.log(Cause.isFailReason(cause.reasons[0])) // true
Companion namespace for the Cause interface.
Cause<function (type parameter) E in <E, B, E2, R2>(predicate: Predicate.Predicate<Cause.Cause<E>>, f: (cause: Cause.Cause<E>) => Effect<B, E2, R2>): <A, R>(self: Effect<A, E, R>) => Effect<A | B, E | E2, R | R2>E>) => 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) B in <E, B, E2, R2>(predicate: Predicate.Predicate<Cause.Cause<E>>, f: (cause: Cause.Cause<E>) => Effect<B, E2, R2>): <A, R>(self: Effect<A, E, R>) => Effect<A | B, E | E2, R | R2>B, function (type parameter) E2 in <E, B, E2, R2>(predicate: Predicate.Predicate<Cause.Cause<E>>, f: (cause: Cause.Cause<E>) => Effect<B, E2, R2>): <A, R>(self: Effect<A, E, R>) => Effect<A | B, E | E2, R | R2>E2, function (type parameter) R2 in <E, B, E2, R2>(predicate: Predicate.Predicate<Cause.Cause<E>>, f: (cause: Cause.Cause<E>) => Effect<B, E2, R2>): <A, R>(self: Effect<A, E, R>) => Effect<A | B, E | E2, R | R2>R2>
): <function (type parameter) A in <A, R>(self: Effect<A, E, R>): Effect<A | B, E | E2, R | R2>A, function (type parameter) R in <A, R>(self: Effect<A, E, R>): Effect<A | B, 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, R>(self: Effect<A, E, R>): Effect<A | B, E | E2, R | R2>A, function (type parameter) E in <E, B, E2, R2>(predicate: Predicate.Predicate<Cause.Cause<E>>, f: (cause: Cause.Cause<E>) => Effect<B, E2, R2>): <A, R>(self: Effect<A, E, R>) => Effect<A | B, E | E2, R | R2>E, function (type parameter) R in <A, R>(self: Effect<A, E, R>): Effect<A | B, 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<function (type parameter) A in <A, R>(self: Effect<A, E, R>): Effect<A | B, E | E2, R | R2>A | function (type parameter) B in <E, B, E2, R2>(predicate: Predicate.Predicate<Cause.Cause<E>>, f: (cause: Cause.Cause<E>) => Effect<B, E2, R2>): <A, R>(self: Effect<A, E, R>) => Effect<A | B, E | E2, R | R2>B, function (type parameter) E in <E, B, E2, R2>(predicate: Predicate.Predicate<Cause.Cause<E>>, f: (cause: Cause.Cause<E>) => Effect<B, E2, R2>): <A, R>(self: Effect<A, E, R>) => Effect<A | B, E | E2, R | R2>E | function (type parameter) E2 in <E, B, E2, R2>(predicate: Predicate.Predicate<Cause.Cause<E>>, f: (cause: Cause.Cause<E>) => Effect<B, E2, R2>): <A, R>(self: Effect<A, E, R>) => Effect<A | B, E | E2, R | R2>E2, function (type parameter) R in <A, R>(self: Effect<A, E, R>): Effect<A | B, E | E2, R | R2>R | function (type parameter) R2 in <E, B, E2, R2>(predicate: Predicate.Predicate<Cause.Cause<E>>, f: (cause: Cause.Cause<E>) => Effect<B, E2, R2>): <A, R>(self: Effect<A, E, R>) => Effect<A | B, E | E2, R | R2>R2>
<function (type parameter) A in <A, E, R, B, E2, R2>(self: Effect<A, E, R>, predicate: Predicate.Predicate<Cause.Cause<E>>, f: (cause: Cause.Cause<E>) => Effect<B, E2, R2>): Effect<A | B, E | E2, R | R2>A, function (type parameter) E in <A, E, R, B, E2, R2>(self: Effect<A, E, R>, predicate: Predicate.Predicate<Cause.Cause<E>>, f: (cause: Cause.Cause<E>) => Effect<B, E2, R2>): Effect<A | B, E | E2, R | R2>E, function (type parameter) R in <A, E, R, B, E2, R2>(self: Effect<A, E, R>, predicate: Predicate.Predicate<Cause.Cause<E>>, f: (cause: Cause.Cause<E>) => Effect<B, E2, R2>): Effect<A | B, E | E2, R | R2>R, function (type parameter) B in <A, E, R, B, E2, R2>(self: Effect<A, E, R>, predicate: Predicate.Predicate<Cause.Cause<E>>, f: (cause: Cause.Cause<E>) => Effect<B, E2, R2>): Effect<A | B, E | E2, R | R2>B, function (type parameter) E2 in <A, E, R, B, E2, R2>(self: Effect<A, E, R>, predicate: Predicate.Predicate<Cause.Cause<E>>, f: (cause: Cause.Cause<E>) => Effect<B, E2, R2>): Effect<A | B, E | E2, R | R2>E2, function (type parameter) R2 in <A, E, R, B, E2, R2>(self: Effect<A, E, R>, predicate: Predicate.Predicate<Cause.Cause<E>>, f: (cause: Cause.Cause<E>) => Effect<B, E2, R2>): Effect<A | B, E | E2, R | R2>R2>(
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, B, E2, R2>(self: Effect<A, E, R>, predicate: Predicate.Predicate<Cause.Cause<E>>, f: (cause: Cause.Cause<E>) => Effect<B, E2, R2>): Effect<A | B, E | E2, R | R2>A, function (type parameter) E in <A, E, R, B, E2, R2>(self: Effect<A, E, R>, predicate: Predicate.Predicate<Cause.Cause<E>>, f: (cause: Cause.Cause<E>) => Effect<B, E2, R2>): Effect<A | B, E | E2, R | R2>E, function (type parameter) R in <A, E, R, B, E2, R2>(self: Effect<A, E, R>, predicate: Predicate.Predicate<Cause.Cause<E>>, f: (cause: Cause.Cause<E>) => Effect<B, E2, R2>): Effect<A | B, E | E2, R | R2>R>,
predicate: Predicate.Predicate<Cause.Cause<E>>predicate: import PredicatePredicate.interface Predicate<in A>A function that decides whether a value of type A satisfies a condition.
When to use
Use when you want a reusable boolean check for A, especially when you plan
to combine checks with
and
/
or
or pass a predicate to arrays
and iterables.
Details
A predicate returns true or false and never throws by itself. It does not
narrow types unless you use Refinement.
Example (Defining a predicate)
import { Predicate } from "effect"
const isPositive: Predicate.Predicate<number> = (n) => n > 0
console.log(isPositive(1))
Type-level utilities for working with
Predicate
types.
When to use
Use when you need to extract input types from predicate signatures while
writing generic helpers over predicate types.
Details
These utilities are type-only, create no runtime values, and the namespace is
erased at runtime.
Example (Extracting predicate input)
import { Predicate } from "effect"
type IsString = Predicate.Predicate<string>
type Input = Predicate.Predicate.In<IsString>
Predicate<import CauseCause.interface Cause<out E>A structured representation of how an Effect failed.
When to use
Use to preserve the full structured failure information for an effect instead
of collapsing it to a single error value.
Details
Access the individual failure entries through the reasons array, then
narrow each entry with
isFailReason
,
isDieReason
, or
- Use
hasFails
/
hasDies
/
hasInterrupts
to test
for the presence of specific reason kinds without iterating.
- Use
findError
/
findDefect
to extract the first value
of a given kind.
- Use
combine
to merge two causes.
Cause implements Equal — two causes with the same reasons (by value)
compare as equal.
Example (Creating and inspecting a cause)
import { Cause } from "effect"
const cause = Cause.fail("Something went wrong")
console.log(cause.reasons.length) // 1
console.log(Cause.isFailReason(cause.reasons[0])) // true
Companion namespace for the Cause interface.
Cause<function (type parameter) E in <A, E, R, B, E2, R2>(self: Effect<A, E, R>, predicate: Predicate.Predicate<Cause.Cause<E>>, f: (cause: Cause.Cause<E>) => Effect<B, E2, R2>): Effect<A | B, E | E2, R | R2>E>>,
f: (
cause: Cause.Cause<E>
) => Effect<B, E2, R2>
cause: Cause.Cause<E>(parameter) cause: {
reasons: ReadonlyArray<Reason<E>>;
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 CauseCause.interface Cause<out E>A structured representation of how an Effect failed.
When to use
Use to preserve the full structured failure information for an effect instead
of collapsing it to a single error value.
Details
Access the individual failure entries through the reasons array, then
narrow each entry with
isFailReason
,
isDieReason
, or
- Use
hasFails
/
hasDies
/
hasInterrupts
to test
for the presence of specific reason kinds without iterating.
- Use
findError
/
findDefect
to extract the first value
of a given kind.
- Use
combine
to merge two causes.
Cause implements Equal — two causes with the same reasons (by value)
compare as equal.
Example (Creating and inspecting a cause)
import { Cause } from "effect"
const cause = Cause.fail("Something went wrong")
console.log(cause.reasons.length) // 1
console.log(Cause.isFailReason(cause.reasons[0])) // true
Companion namespace for the Cause interface.
Cause<function (type parameter) E in <A, E, R, B, E2, R2>(self: Effect<A, E, R>, predicate: Predicate.Predicate<Cause.Cause<E>>, f: (cause: Cause.Cause<E>) => Effect<B, E2, R2>): Effect<A | B, E | E2, R | R2>E>) => 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) B in <A, E, R, B, E2, R2>(self: Effect<A, E, R>, predicate: Predicate.Predicate<Cause.Cause<E>>, f: (cause: Cause.Cause<E>) => Effect<B, E2, R2>): Effect<A | B, E | E2, R | R2>B, function (type parameter) E2 in <A, E, R, B, E2, R2>(self: Effect<A, E, R>, predicate: Predicate.Predicate<Cause.Cause<E>>, f: (cause: Cause.Cause<E>) => Effect<B, E2, R2>): Effect<A | B, E | E2, R | R2>E2, function (type parameter) R2 in <A, E, R, B, E2, R2>(self: Effect<A, E, R>, predicate: Predicate.Predicate<Cause.Cause<E>>, f: (cause: Cause.Cause<E>) => Effect<B, E2, R2>): Effect<A | B, 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<function (type parameter) A in <A, E, R, B, E2, R2>(self: Effect<A, E, R>, predicate: Predicate.Predicate<Cause.Cause<E>>, f: (cause: Cause.Cause<E>) => Effect<B, E2, R2>): Effect<A | B, E | E2, R | R2>A | function (type parameter) B in <A, E, R, B, E2, R2>(self: Effect<A, E, R>, predicate: Predicate.Predicate<Cause.Cause<E>>, f: (cause: Cause.Cause<E>) => Effect<B, E2, R2>): Effect<A | B, E | E2, R | R2>B, function (type parameter) E in <A, E, R, B, E2, R2>(self: Effect<A, E, R>, predicate: Predicate.Predicate<Cause.Cause<E>>, f: (cause: Cause.Cause<E>) => Effect<B, E2, R2>): Effect<A | B, E | E2, R | R2>E | function (type parameter) E2 in <A, E, R, B, E2, R2>(self: Effect<A, E, R>, predicate: Predicate.Predicate<Cause.Cause<E>>, f: (cause: Cause.Cause<E>) => Effect<B, E2, R2>): Effect<A | B, E | E2, R | R2>E2, function (type parameter) R in <A, E, R, B, E2, R2>(self: Effect<A, E, R>, predicate: Predicate.Predicate<Cause.Cause<E>>, f: (cause: Cause.Cause<E>) => Effect<B, E2, R2>): Effect<A | B, E | E2, R | R2>R | function (type parameter) R2 in <A, E, R, B, E2, R2>(self: Effect<A, E, R>, predicate: Predicate.Predicate<Cause.Cause<E>>, f: (cause: Cause.Cause<E>) => Effect<B, E2, R2>): Effect<A | B, E | E2, R | R2>R2>
} = import internalinternal.const catchCauseIf: {
<E, B, E2, R2>(
predicate: Predicate.Predicate<
Cause.Cause<E>
>,
f: (
cause: Cause.Cause<E>
) => Effect.Effect<B, E2, R2>
): <A, R>(
self: Effect.Effect<A, E, R>
) => Effect.Effect<A | B, E | E2, R | R2>
<A, E, R, B, E2, R2>(
self: Effect.Effect<A, E, R>,
predicate: Predicate.Predicate<
Cause.Cause<E>
>,
f: (
cause: Cause.Cause<E>
) => Effect.Effect<B, E2, R2>
): Effect.Effect<A | B, E | E2, R | R2>
}