<A, R>(f: (current: NoInfer<A>) => [returnValue: R, newValue: A]): (
self: TxRef<A>
) => Effect.Effect<R>
<A, R>(
self: TxRef<A>,
f: (current: A) => [returnValue: R, newValue: A]
): Effect.Effect<R>Modifies the value of the TxRef using the provided function.
When to use
Use to update a TxRef and return a computed result from the same
transaction step.
Example (Modifying transactional references)
import { Effect, TxRef } from "effect"
const program = Effect.gen(function*() {
const counter = yield* TxRef.make(0)
// Modify and return both old and new value
const result = yield* TxRef.modify(counter, (current) => [current * 2, current + 1])
console.log(result) // 0 (the return value: current * 2)
console.log(yield* TxRef.get(counter)) // 1 (the new value: current + 1)
})export const const modify: {
<A, R>(
f: (
current: NoInfer<A>
) => [returnValue: R, newValue: A]
): (self: TxRef<A>) => Effect.Effect<R>
<A, R>(
self: TxRef<A>,
f: (
current: A
) => [returnValue: R, newValue: A]
): Effect.Effect<R>
}
Modifies the value of the TxRef using the provided function.
When to use
Use to update a TxRef and return a computed result from the same
transaction step.
Example (Modifying transactional references)
import { Effect, TxRef } from "effect"
const program = Effect.gen(function*() {
const counter = yield* TxRef.make(0)
// Modify and return both old and new value
const result = yield* TxRef.modify(counter, (current) => [current * 2, current + 1])
console.log(result) // 0 (the return value: current * 2)
console.log(yield* TxRef.get(counter)) // 1 (the new value: current + 1)
})
modify: {
<function (type parameter) A in <A, R>(f: (current: NoInfer<A>) => [returnValue: R, newValue: A]): (self: TxRef<A>) => Effect.Effect<R>A, function (type parameter) R in <A, R>(f: (current: NoInfer<A>) => [returnValue: R, newValue: A]): (self: TxRef<A>) => Effect.Effect<R>R>(f: (
current: NoInfer<A>
) => [returnValue: R, newValue: A]
current: NoInfer<A>current: type NoInfer<A> = [A][A extends any ? 0 : never]Prevents TypeScript from inferring a type parameter from a specific
position.
When to use
Use when a function parameter must match an inferred type without becoming
an inference source.
Details
The parameter using NoInfer must still match the inferred type.
Example (Controlling inference)
import type { Types } from "effect"
declare function withDefault<T>(value: T, fallback: Types.NoInfer<T>): T
// T is inferred as "a" | "b" from the first argument only
const result = withDefault<"a" | "b">("a", "b")
NoInfer<function (type parameter) A in <A, R>(f: (current: NoInfer<A>) => [returnValue: R, newValue: A]): (self: TxRef<A>) => Effect.Effect<R>A>) => [RreturnValue: function (type parameter) R in <A, R>(f: (current: NoInfer<A>) => [returnValue: R, newValue: A]): (self: TxRef<A>) => Effect.Effect<R>R, AnewValue: function (type parameter) A in <A, R>(f: (current: NoInfer<A>) => [returnValue: R, newValue: A]): (self: TxRef<A>) => Effect.Effect<R>A]): (self: TxRef<A>(parameter) self: {
version: number;
pending: Map<unknown, () => void>;
value: 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 TxRef<in out A>TxRef is a transactional value, it can be read and modified within the body of a transaction.
When to use
Use to store mutable state that must be read and modified inside Effect
transactions.
Details
Accessed values are tracked by the transaction in order to detect conflicts and in order to
track changes, a transaction will retry whenever a conflict is detected or whenever the
transaction explicitely calls to Effect.txRetry and any of the accessed TxRef values
change.
Example (Using a transactional reference)
import { Effect, TxRef } from "effect"
const program = Effect.gen(function*() {
// Create a transactional reference
const ref: TxRef.TxRef<number> = yield* TxRef.make(0)
// Use within a transaction
yield* Effect.tx(Effect.gen(function*() {
const current = yield* TxRef.get(ref)
yield* TxRef.set(ref, current + 1)
}))
const final = yield* TxRef.get(ref)
console.log(final) // 1
})
TxRef<function (type parameter) A in <A, R>(f: (current: NoInfer<A>) => [returnValue: R, newValue: A]): (self: TxRef<A>) => Effect.Effect<R>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) R in <A, R>(f: (current: NoInfer<A>) => [returnValue: R, newValue: A]): (self: TxRef<A>) => Effect.Effect<R>R>
<function (type parameter) A in <A, R>(self: TxRef<A>, f: (current: A) => [returnValue: R, newValue: A]): Effect.Effect<R>A, function (type parameter) R in <A, R>(self: TxRef<A>, f: (current: A) => [returnValue: R, newValue: A]): Effect.Effect<R>R>(self: TxRef<A>(parameter) self: {
version: number;
pending: Map<unknown, () => void>;
value: 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 TxRef<in out A>TxRef is a transactional value, it can be read and modified within the body of a transaction.
When to use
Use to store mutable state that must be read and modified inside Effect
transactions.
Details
Accessed values are tracked by the transaction in order to detect conflicts and in order to
track changes, a transaction will retry whenever a conflict is detected or whenever the
transaction explicitely calls to Effect.txRetry and any of the accessed TxRef values
change.
Example (Using a transactional reference)
import { Effect, TxRef } from "effect"
const program = Effect.gen(function*() {
// Create a transactional reference
const ref: TxRef.TxRef<number> = yield* TxRef.make(0)
// Use within a transaction
yield* Effect.tx(Effect.gen(function*() {
const current = yield* TxRef.get(ref)
yield* TxRef.set(ref, current + 1)
}))
const final = yield* TxRef.get(ref)
console.log(final) // 1
})
TxRef<function (type parameter) A in <A, R>(self: TxRef<A>, f: (current: A) => [returnValue: R, newValue: A]): Effect.Effect<R>A>, f: (
current: A
) => [returnValue: R, newValue: A]
current: Acurrent: function (type parameter) A in <A, R>(self: TxRef<A>, f: (current: A) => [returnValue: R, newValue: A]): Effect.Effect<R>A) => [RreturnValue: function (type parameter) R in <A, R>(self: TxRef<A>, f: (current: A) => [returnValue: R, newValue: A]): Effect.Effect<R>R, AnewValue: function (type parameter) A in <A, R>(self: TxRef<A>, f: (current: A) => [returnValue: R, newValue: A]): Effect.Effect<R>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) R in <A, R>(self: TxRef<A>, f: (current: A) => [returnValue: R, newValue: A]): Effect.Effect<R>R>
} = dual<(...args: Array<any>) => any, <A, R>(self: TxRef<A>, f: (current: A) => [returnValue: R, newValue: A]) => Effect.Effect<R>>(arity: 2, body: <A, R>(self: TxRef<A>, f: (current: A) => [returnValue: R, newValue: A]) => Effect.Effect<R>): ((...args: Array<any>) => any) & (<A, R>(self: TxRef<A>, f: (current: A) => [returnValue: R, newValue: A]) => Effect.Effect<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(2, <function (type parameter) A in <A, R>(self: TxRef<A>, f: (current: A) => [returnValue: R, newValue: A]): Effect.Effect<R>A, function (type parameter) R in <A, R>(self: TxRef<A>, f: (current: A) => [returnValue: R, newValue: A]): Effect.Effect<R>R>(
self: TxRef<A>(parameter) self: {
version: number;
pending: Map<unknown, () => void>;
value: 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 TxRef<in out A>TxRef is a transactional value, it can be read and modified within the body of a transaction.
When to use
Use to store mutable state that must be read and modified inside Effect
transactions.
Details
Accessed values are tracked by the transaction in order to detect conflicts and in order to
track changes, a transaction will retry whenever a conflict is detected or whenever the
transaction explicitely calls to Effect.txRetry and any of the accessed TxRef values
change.
Example (Using a transactional reference)
import { Effect, TxRef } from "effect"
const program = Effect.gen(function*() {
// Create a transactional reference
const ref: TxRef.TxRef<number> = yield* TxRef.make(0)
// Use within a transaction
yield* Effect.tx(Effect.gen(function*() {
const current = yield* TxRef.get(ref)
yield* TxRef.set(ref, current + 1)
}))
const final = yield* TxRef.get(ref)
console.log(final) // 1
})
TxRef<function (type parameter) A in <A, R>(self: TxRef<A>, f: (current: A) => [returnValue: R, newValue: A]): Effect.Effect<R>A>,
f: (
current: A
) => [returnValue: R, newValue: A]
current: Acurrent: function (type parameter) A in <A, R>(self: TxRef<A>, f: (current: A) => [returnValue: R, newValue: A]): Effect.Effect<R>A) => [RreturnValue: function (type parameter) R in <A, R>(self: TxRef<A>, f: (current: A) => [returnValue: R, newValue: A]): Effect.Effect<R>R, AnewValue: function (type parameter) A in <A, R>(self: TxRef<A>, f: (current: A) => [returnValue: R, newValue: A]): Effect.Effect<R>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) R in <A, R>(self: TxRef<A>, f: (current: A) => [returnValue: R, newValue: A]): Effect.Effect<R>R> =>
import EffectEffect.class Transactionclass Transaction {
key: Identifier;
Service: {
retry: boolean;
journal: Map<TxRef<any>, { readonly version: number; value: any }>;
};
of: (this: void, self: { retry: boolean; readonly journal: Map<TxRef<any>, { readonly version: number; value: any }> }) => { retry: boolean; readonly journal: Map<TxRef<any>, { readonly version: number; value: any }> };
context: (self: { retry: boolean; readonly journal: Map<TxRef<any>, { readonly version: number; value: any }> }) => Context<Effect.Transaction>;
use: (f: (service: { retry: boolean; readonly journal: Map<TxRef<any>, { readonly version: number; value: any }> }) => Effect.Effect<A, E, R>) => Effect.Effect<A, E, Effect.Transaction | R>;
useSync: (f: (service: { retry: boolean; readonly journal: Map<TxRef<any>, { readonly version: number; value: any }> }) => A) => Effect.Effect<A, never, Effect.Transaction>;
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;
}
Service that holds the current transaction state.
Details
It includes a journal that stores non-committed changes to TxRef values and
a retry flag that records whether the transaction should be retried.
Example (Building transactions)
import { Effect } from "effect"
// Transaction class for software transactional memory operations
const txEffect = Effect.gen(function*() {
const tx = yield* Effect.Transaction
// Use transaction for coordinated state changes
return "Transaction complete"
})
Transaction.Pipeable.pipe<typeof Effect.Transaction, Effect.Effect<R, never, Effect.Transaction>, Effect.Effect<R, never, never>>(this: typeof Effect.Transaction, ab: (_: typeof Effect.Transaction) => Effect.Effect<R, never, Effect.Transaction>, bc: (_: Effect.Effect<R, never, Effect.Transaction>) => Effect.Effect<R, never, never>): Effect.Effect<R, never, never> (+21 overloads)pipe(
import EffectEffect.const flatMap: {
<A, B, E1, R1>(
f: (a: A) => Effect<B, E1, R1>
): <E, R>(
self: Effect<A, E, R>
) => Effect<B, E1 | E, R1 | R>
<A, E, R, B, E1, R1>(
self: Effect<A, E, R>,
f: (a: A) => Effect<B, E1, R1>
): Effect<B, E | E1, R | R1>
}
state: {
retry: boolean
readonly journal: Map<
TxRef<any>,
{ readonly version: number; value: any }
>
}
import EffectEffect.const sync: <A>(
thunk: LazyArg<A>
) => Effect<A>
Creates an Effect that represents a synchronous side-effectful computation.
When to use
Use when you need to wrap a synchronous side-effectful operation that is not
expected to throw.
Details
The provided function is evaluated lazily when the effect runs.
Gotchas
The function must not throw. If it throws, the thrown value is treated as a
defect, not as a typed failure. Use try when throwing is expected.
Example (Capturing synchronous logging in an Effect)
import { Effect } from "effect"
const log = (message: string) =>
Effect.sync(() => {
console.log(message) // side effect
})
// ┌─── Effect<void, never, never>
// ▼
const program = log("Hello, World!")
sync(() => {
if (!state: {
retry: boolean
readonly journal: Map<
TxRef<any>,
{ readonly version: number; value: any }
>
}
journal: Map<
TxRef<any>,
{ readonly version: number; value: any }
>
Map<TxRef<any>, { readonly version: number; value: any; }>.has(key: TxRef<any>): booleanhas(self: TxRef<A>(parameter) self: {
version: number;
pending: Map<unknown, () => void>;
value: 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; <…;
}
state: {
retry: boolean
readonly journal: Map<
TxRef<any>,
{ readonly version: number; value: any }
>
}
journal: Map<
TxRef<any>,
{ readonly version: number; value: any }
>
Map<TxRef<any>, { readonly version: number; value: any; }>.set(key: TxRef<any>, value: {
readonly version: number;
value: any;
}): Map<TxRef<any>, {
readonly version: number;
value: any;
}>
Adds a new element with a specified key and value to the Map. If an element with the same key already exists, the element will be updated.
set(self: TxRef<A>(parameter) self: {
version: number;
pending: Map<unknown, () => void>;
value: 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; <…;
}
version: numberversion: self: TxRef<A>(parameter) self: {
version: number;
pending: Map<unknown, () => void>;
value: 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; <…;
}
TxRef<in out A>.version: numberversion, value: anyvalue: self: TxRef<A>(parameter) self: {
version: number;
pending: Map<unknown, () => void>;
value: 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; <…;
}
TxRef<A>.value: Avalue })
}
const const current: {
readonly version: number
value: any
}
state: {
retry: boolean
readonly journal: Map<
TxRef<any>,
{ readonly version: number; value: any }
>
}
journal: Map<
TxRef<any>,
{ readonly version: number; value: any }
>
Map<TxRef<any>, { readonly version: number; value: any; }>.get(key: TxRef<any>): {
readonly version: number;
value: any;
} | undefined
Returns a specified element from the Map object. If the value that is associated to the provided key is an object, then you will get a reference to that object and any change made to that object will effectively modify it inside the Map.
get(self: TxRef<A>(parameter) self: {
version: number;
pending: Map<unknown, () => void>;
value: 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; <…;
}
const returnValue: RreturnValue, const next: Anext] = f: (
current: A
) => [returnValue: R, newValue: A]
const current: {
readonly version: number
value: any
}
value: anyvalue)
const current: {
readonly version: number
value: any
}
value: anyvalue = const next: Anext
return const returnValue: RreturnValue
})
),
import EffectEffect.const tx: <A, E, R>(
effect: Effect<A, E, R>
) => Effect<A, E, Exclude<R, Transaction>>
Defines a transaction boundary. Transactions are "all or nothing" with respect to changes
made to transactional values (i.e. TxRef) that occur within the transaction body.
Details
If called inside an active transaction, tx composes with the current transaction and reuses
its journal and retry state instead of creating a nested boundary.
Effect transactions are optimistic with retry. A transaction is retried when
its body explicitly calls Effect.txRetry and any accessed transactional
value changes, or when any accessed transactional value changes because a
different transaction commits before the current one.
The outermost tx call creates the transaction boundary and commits or rolls back the full
composed transaction.
Example (Running a transaction)
import { Effect, TxRef } from "effect"
const program = Effect.gen(function*() {
const ref1 = yield* TxRef.make(0)
const ref2 = yield* TxRef.make(0)
// Nested tx calls compose into the same transaction
yield* Effect.tx(Effect.gen(function*() {
yield* TxRef.set(ref1, 10)
yield* Effect.tx(TxRef.set(ref2, 20))
const sum = (yield* TxRef.get(ref1)) + (yield* TxRef.get(ref2))
console.log(`Transaction sum: ${sum}`)
}))
console.log(`Final ref1: ${yield* TxRef.get(ref1)}`) // 10
console.log(`Final ref2: ${yield* TxRef.get(ref2)}`) // 20
})
tx
))