<B, A>(pf: (a: A) => readonly [B, Option.Option<A>]): (
self: Ref<A>
) => Effect.Effect<B>
<A, B>(
self: Ref<A>,
pf: (a: A) => readonly [B, Option.Option<A>]
): Effect.Effect<B>Computes a result atomically and optionally updates the value of the Ref.
When to use
Use to compute a return value while optionally updating a plain Ref.
Details
The callback receives the current value and returns [result, nextValue],
where nextValue is an Option. If nextValue is Option.some(value),
the Ref is updated to value; if it is Option.none(), the Ref is left
unchanged. The returned effect always succeeds with result.
Example (Conditionally modifying a value)
import { Effect, Option, Ref } from "effect"
const program = Effect.gen(function*() {
const counter = yield* Ref.make(5)
// Only modify if value is greater than 3
const result1 = yield* Ref.modifySome(
counter,
(n) =>
n > 3
? [`incremented ${n}`, Option.some(n + 10)]
: ["no change", Option.none()]
)
console.log(result1) // "incremented 5"
const current1 = yield* Ref.get(counter)
console.log(current1) // 15
// Try to modify with a condition that fails
const result2 = yield* Ref.modifySome(
counter,
(n) =>
n < 10
? [`decremented ${n}`, Option.some(n - 5)]
: ["no change", Option.none()]
)
console.log(result2) // "no change"
const current2 = yield* Ref.get(counter)
console.log(current2) // 15 (unchanged)
})export const const modifySome: {
<B, A>(
pf: (a: A) => readonly [B, Option.Option<A>]
): (self: Ref<A>) => Effect.Effect<B>
<A, B>(
self: Ref<A>,
pf: (a: A) => readonly [B, Option.Option<A>]
): Effect.Effect<B>
}
Computes a result atomically and optionally updates the value of the Ref.
When to use
Use to compute a return value while optionally updating a plain Ref.
Details
The callback receives the current value and returns [result, nextValue],
where nextValue is an Option. If nextValue is Option.some(value),
the Ref is updated to value; if it is Option.none(), the Ref is left
unchanged. The returned effect always succeeds with result.
Example (Conditionally modifying a value)
import { Effect, Option, Ref } from "effect"
const program = Effect.gen(function*() {
const counter = yield* Ref.make(5)
// Only modify if value is greater than 3
const result1 = yield* Ref.modifySome(
counter,
(n) =>
n > 3
? [`incremented ${n}`, Option.some(n + 10)]
: ["no change", Option.none()]
)
console.log(result1) // "incremented 5"
const current1 = yield* Ref.get(counter)
console.log(current1) // 15
// Try to modify with a condition that fails
const result2 = yield* Ref.modifySome(
counter,
(n) =>
n < 10
? [`decremented ${n}`, Option.some(n - 5)]
: ["no change", Option.none()]
)
console.log(result2) // "no change"
const current2 = yield* Ref.get(counter)
console.log(current2) // 15 (unchanged)
})
modifySome: {
<function (type parameter) B in <B, A>(pf: (a: A) => readonly [B, Option.Option<A>]): (self: Ref<A>) => Effect.Effect<B>B, function (type parameter) A in <B, A>(pf: (a: A) => readonly [B, Option.Option<A>]): (self: Ref<A>) => Effect.Effect<B>A>(pf: (a: A) => readonly [B, Option.Option<A>]pf: (a: Aa: function (type parameter) A in <B, A>(pf: (a: A) => readonly [B, Option.Option<A>]): (self: Ref<A>) => Effect.Effect<B>A) => readonly [function (type parameter) B in <B, A>(pf: (a: A) => readonly [B, Option.Option<A>]): (self: Ref<A>) => Effect.Effect<B>B, import OptionOption.type Option<A> = Option.None<A> | Option.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 <B, A>(pf: (a: A) => readonly [B, Option.Option<A>]): (self: Ref<A>) => Effect.Effect<B>A>]): (self: Ref<A>(parameter) self: {
ref: MutableRef.MutableRef<A>;
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 Ref<in out A>A mutable reference that provides atomic read, write, and update operations.
When to use
Use to keep shared mutable state that is read and updated inside Effect
programs.
Details
A Ref is a thread-safe mutable reference type for shared state. It supports
simple read and write operations as well as atomic transformations.
Example (Reading and updating a ref)
import { Effect, Ref } from "effect"
const program = Effect.gen(function*() {
// Create a ref with initial value
const counter = yield* Ref.make(0)
// Read the current value
const value = yield* Ref.get(counter)
console.log(value) // 0
// Update the value atomically
yield* Ref.update(counter, (n) => n + 1)
// Read the updated value
const newValue = yield* Ref.get(counter)
console.log(newValue) // 1
})
The Ref namespace containing type definitions and utilities.
When to use
Use when referring to type members nested under the Ref namespace.
Ref<function (type parameter) A in <B, A>(pf: (a: A) => readonly [B, Option.Option<A>]): (self: Ref<A>) => Effect.Effect<B>A>) => import EffectEffect.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 <B, A>(pf: (a: A) => readonly [B, Option.Option<A>]): (self: Ref<A>) => Effect.Effect<B>B>
<function (type parameter) A in <A, B>(self: Ref<A>, pf: (a: A) => readonly [B, Option.Option<A>]): Effect.Effect<B>A, function (type parameter) B in <A, B>(self: Ref<A>, pf: (a: A) => readonly [B, Option.Option<A>]): Effect.Effect<B>B>(self: Ref<A>(parameter) self: {
ref: MutableRef.MutableRef<A>;
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 Ref<in out A>A mutable reference that provides atomic read, write, and update operations.
When to use
Use to keep shared mutable state that is read and updated inside Effect
programs.
Details
A Ref is a thread-safe mutable reference type for shared state. It supports
simple read and write operations as well as atomic transformations.
Example (Reading and updating a ref)
import { Effect, Ref } from "effect"
const program = Effect.gen(function*() {
// Create a ref with initial value
const counter = yield* Ref.make(0)
// Read the current value
const value = yield* Ref.get(counter)
console.log(value) // 0
// Update the value atomically
yield* Ref.update(counter, (n) => n + 1)
// Read the updated value
const newValue = yield* Ref.get(counter)
console.log(newValue) // 1
})
The Ref namespace containing type definitions and utilities.
When to use
Use when referring to type members nested under the Ref namespace.
Ref<function (type parameter) A in <A, B>(self: Ref<A>, pf: (a: A) => readonly [B, Option.Option<A>]): Effect.Effect<B>A>, pf: (a: A) => readonly [B, Option.Option<A>]pf: (a: Aa: function (type parameter) A in <A, B>(self: Ref<A>, pf: (a: A) => readonly [B, Option.Option<A>]): Effect.Effect<B>A) => readonly [function (type parameter) B in <A, B>(self: Ref<A>, pf: (a: A) => readonly [B, Option.Option<A>]): Effect.Effect<B>B, import OptionOption.type Option<A> = Option.None<A> | Option.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, B>(self: Ref<A>, pf: (a: A) => readonly [B, Option.Option<A>]): Effect.Effect<B>A>]): import EffectEffect.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, B>(self: Ref<A>, pf: (a: A) => readonly [B, Option.Option<A>]): Effect.Effect<B>B>
} = dual<<B, A>(pf: (a: A) => readonly [B, Option.Option<A>]) => (self: Ref<A>) => Effect.Effect<B>, <A, B>(self: Ref<A>, pf: (a: A) => readonly [B, Option.Option<A>]) => Effect.Effect<B>>(arity: 2, body: <A, B>(self: Ref<A>, pf: (a: A) => readonly [B, Option.Option<A>]) => Effect.Effect<B>): (<B, A>(pf: (a: A) => readonly [B, Option.Option<A>]) => (self: Ref<A>) => Effect.Effect<B>) & (<A, B>(self: Ref<A>, pf: (a: A) => readonly [B, Option.Option<A>]) => Effect.Effect<B>) (+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) B in <B, A>(pf: (a: A) => readonly [B, Option.Option<A>]): (self: Ref<A>) => Effect.Effect<B>B, function (type parameter) A in <B, A>(pf: (a: A) => readonly [B, Option.Option<A>]): (self: Ref<A>) => Effect.Effect<B>A>(
pf: (a: A) => readonly [B, Option.Option<A>]pf: (a: Aa: function (type parameter) A in <B, A>(pf: (a: A) => readonly [B, Option.Option<A>]): (self: Ref<A>) => Effect.Effect<B>A) => readonly [function (type parameter) B in <B, A>(pf: (a: A) => readonly [B, Option.Option<A>]): (self: Ref<A>) => Effect.Effect<B>B, import OptionOption.type Option<A> = Option.None<A> | Option.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 <B, A>(pf: (a: A) => readonly [B, Option.Option<A>]): (self: Ref<A>) => Effect.Effect<B>A>]
) => (self: Ref<A>(parameter) self: {
ref: MutableRef.MutableRef<A>;
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 Ref<in out A>A mutable reference that provides atomic read, write, and update operations.
When to use
Use to keep shared mutable state that is read and updated inside Effect
programs.
Details
A Ref is a thread-safe mutable reference type for shared state. It supports
simple read and write operations as well as atomic transformations.
Example (Reading and updating a ref)
import { Effect, Ref } from "effect"
const program = Effect.gen(function*() {
// Create a ref with initial value
const counter = yield* Ref.make(0)
// Read the current value
const value = yield* Ref.get(counter)
console.log(value) // 0
// Update the value atomically
yield* Ref.update(counter, (n) => n + 1)
// Read the updated value
const newValue = yield* Ref.get(counter)
console.log(newValue) // 1
})
The Ref namespace containing type definitions and utilities.
When to use
Use when referring to type members nested under the Ref namespace.
Ref<function (type parameter) A in <B, A>(pf: (a: A) => readonly [B, Option.Option<A>]): (self: Ref<A>) => Effect.Effect<B>A>) => import EffectEffect.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 <B, A>(pf: (a: A) => readonly [B, Option.Option<A>]): (self: Ref<A>) => Effect.Effect<B>B>,
<function (type parameter) A in <A, B>(self: Ref<A>, pf: (a: A) => readonly [B, Option.Option<A>]): Effect.Effect<B>A, function (type parameter) B in <A, B>(self: Ref<A>, pf: (a: A) => readonly [B, Option.Option<A>]): Effect.Effect<B>B>(
self: Ref<A>(parameter) self: {
ref: MutableRef.MutableRef<A>;
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 Ref<in out A>A mutable reference that provides atomic read, write, and update operations.
When to use
Use to keep shared mutable state that is read and updated inside Effect
programs.
Details
A Ref is a thread-safe mutable reference type for shared state. It supports
simple read and write operations as well as atomic transformations.
Example (Reading and updating a ref)
import { Effect, Ref } from "effect"
const program = Effect.gen(function*() {
// Create a ref with initial value
const counter = yield* Ref.make(0)
// Read the current value
const value = yield* Ref.get(counter)
console.log(value) // 0
// Update the value atomically
yield* Ref.update(counter, (n) => n + 1)
// Read the updated value
const newValue = yield* Ref.get(counter)
console.log(newValue) // 1
})
The Ref namespace containing type definitions and utilities.
When to use
Use when referring to type members nested under the Ref namespace.
Ref<function (type parameter) A in <A, B>(self: Ref<A>, pf: (a: A) => readonly [B, Option.Option<A>]): Effect.Effect<B>A>,
pf: (a: A) => readonly [B, Option.Option<A>]pf: (a: Aa: function (type parameter) A in <A, B>(self: Ref<A>, pf: (a: A) => readonly [B, Option.Option<A>]): Effect.Effect<B>A) => readonly [function (type parameter) B in <A, B>(self: Ref<A>, pf: (a: A) => readonly [B, Option.Option<A>]): Effect.Effect<B>B, import OptionOption.type Option<A> = Option.None<A> | Option.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, B>(self: Ref<A>, pf: (a: A) => readonly [B, Option.Option<A>]): Effect.Effect<B>A>]
) => import EffectEffect.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, B>(self: Ref<A>, pf: (a: A) => readonly [B, Option.Option<A>]): Effect.Effect<B>B>
>(2, (self: Ref<A>(parameter) self: {
ref: MutableRef.MutableRef<A>;
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; <…;
}
pf: (a: A) => readonly [B, Option.Option<A>]pf) =>
const modify: (<A, B>(
f: (a: A) => readonly [B, A]
) => (self: Ref<A>) => Effect.Effect<B>) &
(<A, B>(
self: Ref<A>,
f: (a: A) => readonly [B, A]
) => Effect.Effect<B>)
self: Ref<A>(parameter) self: {
ref: MutableRef.MutableRef<A>;
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; <…;
}
value: Avalue) => {
const [const b: Bb, const option: Option.Option<A>option] = pf: (a: A) => readonly [B, Option.Option<A>]pf(value: Avalue)
return [const b: Bb, const option: Option.Option<A>option._tag: "None" | "Some"_tag === "None" ? value: Avalue : const option: Option.Some<A>const option: {
_tag: "Some";
_op: "Some";
value: A;
valueOrUndefined: A;
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;
}
Some<A>.value: Avalue]
}))