<A, B, X>(f: (input: NoInfer<A>, i: number) => Result.Result<B, X>): (
self: Iterable<A>
) => Array<B>
<A, B, X>(
self: Iterable<A>,
f: (input: A, i: number) => Result.Result<B, X>
): Array<B>Keeps transformed values for elements where a Filter succeeds.
When to use
Use to filter an iterable with a Result-returning transformation while
discarding failures.
Details
The filter receives (element, index). Failures are discarded.
Example (Filtering and transforming)
import { Array, Result } from "effect"
console.log(Array.filterMap([1, 2, 3, 4], (n) => n % 2 === 0 ? Result.succeed(n * 10) : Result.failVoid))
// [20, 40]export const const filterMap: {
<A, B, X>(
f: (
input: NoInfer<A>,
i: number
) => Result.Result<B, X>
): (self: Iterable<A>) => Array<B>
<A, B, X>(
self: Iterable<A>,
f: (
input: A,
i: number
) => Result.Result<B, X>
): Array<B>
}
Keeps transformed values for elements where a Filter succeeds.
When to use
Use to filter an iterable with a Result-returning transformation while
discarding failures.
Details
The filter receives (element, index). Failures are discarded.
Example (Filtering and transforming)
import { Array, Result } from "effect"
console.log(Array.filterMap([1, 2, 3, 4], (n) => n % 2 === 0 ? Result.succeed(n * 10) : Result.failVoid))
// [20, 40]
filterMap: {
<function (type parameter) A in <A, B, X>(f: (input: NoInfer<A>, i: number) => Result.Result<B, X>): (self: Iterable<A>) => Array<B>A, function (type parameter) B in <A, B, X>(f: (input: NoInfer<A>, i: number) => Result.Result<B, X>): (self: Iterable<A>) => Array<B>B, function (type parameter) X in <A, B, X>(f: (input: NoInfer<A>, i: number) => Result.Result<B, X>): (self: Iterable<A>) => Array<B>X>(f: (
input: NoInfer<A>,
i: number
) => Result.Result<B, X>
input: NoInfer<A>input: 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, B, X>(f: (input: NoInfer<A>, i: number) => Result.Result<B, X>): (self: Iterable<A>) => Array<B>A>, i: numberi: number) => import ResultResult.type Result<A, E = never> = Result.Success<A, E> | Result.Failure<A, E>A value that is either Success<A, E> or Failure<A, E>.
When to use
Use when both success and failure should remain available as data and
Option would lose failure information.
Details
- Use
succeed
/
fail
to construct
- Use
match
to fold both branches
- Use
isSuccess
/
isFailure
to narrow the type
E defaults to never, so Result<number> means a result that cannot fail.
Example (Creating and matching a Result)
import { Result } from "effect"
const success = Result.succeed(42)
const failure = Result.fail("something went wrong")
const message = Result.match(success, {
onSuccess: (value) => `Success: ${value}`,
onFailure: (error) => `Error: ${error}`
})
console.log(message)
// Output: "Success: 42"
Namespace containing type-level utilities for extracting the inner types
of a Result.
Example (Extracting inner types)
import type { Result } from "effect"
type R = Result.Result<number, string>
// number
type A = Result.Result.Success<R>
// string
type E = Result.Result.Failure<R>
Result<function (type parameter) B in <A, B, X>(f: (input: NoInfer<A>, i: number) => Result.Result<B, X>): (self: Iterable<A>) => Array<B>B, function (type parameter) X in <A, B, X>(f: (input: NoInfer<A>, i: number) => Result.Result<B, X>): (self: Iterable<A>) => Array<B>X>): (self: Iterable<A>self: interface Iterable<T, TReturn = any, TNext = any>Iterable<function (type parameter) A in <A, B, X>(f: (input: NoInfer<A>, i: number) => Result.Result<B, X>): (self: Iterable<A>) => Array<B>A>) => interface Array<T>Array<function (type parameter) B in <A, B, X>(f: (input: NoInfer<A>, i: number) => Result.Result<B, X>): (self: Iterable<A>) => Array<B>B>
<function (type parameter) A in <A, B, X>(self: Iterable<A>, f: (input: A, i: number) => Result.Result<B, X>): Array<B>A, function (type parameter) B in <A, B, X>(self: Iterable<A>, f: (input: A, i: number) => Result.Result<B, X>): Array<B>B, function (type parameter) X in <A, B, X>(self: Iterable<A>, f: (input: A, i: number) => Result.Result<B, X>): Array<B>X>(self: Iterable<A>self: interface Iterable<T, TReturn = any, TNext = any>Iterable<function (type parameter) A in <A, B, X>(self: Iterable<A>, f: (input: A, i: number) => Result.Result<B, X>): Array<B>A>, f: (
input: A,
i: number
) => Result.Result<B, X>
input: Ainput: function (type parameter) A in <A, B, X>(self: Iterable<A>, f: (input: A, i: number) => Result.Result<B, X>): Array<B>A, i: numberi: number) => import ResultResult.type Result<A, E = never> = Result.Success<A, E> | Result.Failure<A, E>A value that is either Success<A, E> or Failure<A, E>.
When to use
Use when both success and failure should remain available as data and
Option would lose failure information.
Details
- Use
succeed
/
fail
to construct
- Use
match
to fold both branches
- Use
isSuccess
/
isFailure
to narrow the type
E defaults to never, so Result<number> means a result that cannot fail.
Example (Creating and matching a Result)
import { Result } from "effect"
const success = Result.succeed(42)
const failure = Result.fail("something went wrong")
const message = Result.match(success, {
onSuccess: (value) => `Success: ${value}`,
onFailure: (error) => `Error: ${error}`
})
console.log(message)
// Output: "Success: 42"
Namespace containing type-level utilities for extracting the inner types
of a Result.
Example (Extracting inner types)
import type { Result } from "effect"
type R = Result.Result<number, string>
// number
type A = Result.Result.Success<R>
// string
type E = Result.Result.Failure<R>
Result<function (type parameter) B in <A, B, X>(self: Iterable<A>, f: (input: A, i: number) => Result.Result<B, X>): Array<B>B, function (type parameter) X in <A, B, X>(self: Iterable<A>, f: (input: A, i: number) => Result.Result<B, X>): Array<B>X>): interface Array<T>Array<function (type parameter) B in <A, B, X>(self: Iterable<A>, f: (input: A, i: number) => Result.Result<B, X>): Array<B>B>
} = dual<(...args: Array<any>) => any, <A, B, X>(self: Iterable<A>, f: (input: A, i: number) => Result.Result<B, X>) => Array<B>>(arity: 2, body: <A, B, X>(self: Iterable<A>, f: (input: A, i: number) => Result.Result<B, X>) => Array<B>): ((...args: Array<any>) => any) & (<A, B, X>(self: Iterable<A>, f: (input: A, i: number) => Result.Result<B, X>) => Array<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(2, <function (type parameter) A in <A, B, X>(self: Iterable<A>, f: (input: A, i: number) => Result.Result<B, X>): Array<B>A, function (type parameter) B in <A, B, X>(self: Iterable<A>, f: (input: A, i: number) => Result.Result<B, X>): Array<B>B, function (type parameter) X in <A, B, X>(self: Iterable<A>, f: (input: A, i: number) => Result.Result<B, X>): Array<B>X>(self: Iterable<A>self: interface Iterable<T, TReturn = any, TNext = any>Iterable<function (type parameter) A in <A, B, X>(self: Iterable<A>, f: (input: A, i: number) => Result.Result<B, X>): Array<B>A>, f: (
input: A,
i: number
) => Result.Result<B, X>
input: Ainput: function (type parameter) A in <A, B, X>(self: Iterable<A>, f: (input: A, i: number) => Result.Result<B, X>): Array<B>A, i: numberi: number) => import ResultResult.type Result<A, E = never> = Result.Success<A, E> | Result.Failure<A, E>A value that is either Success<A, E> or Failure<A, E>.
When to use
Use when both success and failure should remain available as data and
Option would lose failure information.
Details
- Use
succeed
/
fail
to construct
- Use
match
to fold both branches
- Use
isSuccess
/
isFailure
to narrow the type
E defaults to never, so Result<number> means a result that cannot fail.
Example (Creating and matching a Result)
import { Result } from "effect"
const success = Result.succeed(42)
const failure = Result.fail("something went wrong")
const message = Result.match(success, {
onSuccess: (value) => `Success: ${value}`,
onFailure: (error) => `Error: ${error}`
})
console.log(message)
// Output: "Success: 42"
Namespace containing type-level utilities for extracting the inner types
of a Result.
Example (Extracting inner types)
import type { Result } from "effect"
type R = Result.Result<number, string>
// number
type A = Result.Result.Success<R>
// string
type E = Result.Result.Failure<R>
Result<function (type parameter) B in <A, B, X>(self: Iterable<A>, f: (input: A, i: number) => Result.Result<B, X>): Array<B>B, function (type parameter) X in <A, B, X>(self: Iterable<A>, f: (input: A, i: number) => Result.Result<B, X>): Array<B>X>): interface Array<T>Array<function (type parameter) B in <A, B, X>(self: Iterable<A>, f: (input: A, i: number) => Result.Result<B, X>): Array<B>B> => {
const const as: A[]as = const fromIterable: <A>(
collection: Iterable<A>
) => A[]
Converts an Iterable to an Array.
When to use
Use to convert any Iterable (Set, Generator, etc.) into an array.
Details
If the input is already an array, this returns it by reference without
copying. Otherwise, it creates a new array from the iterable. Use copy if
you need a fresh array even when the input is already an array.
Example (Converting a Set to an array)
import { Array } from "effect"
const result = Array.fromIterable(new Set([1, 2, 3]))
console.log(result) // [1, 2, 3]
fromIterable(self: Iterable<A>self)
const const out: B[]out: interface Array<T>Array<function (type parameter) B in <A, B, X>(self: Iterable<A>, f: (input: A, i: number) => Result.Result<B, X>): Array<B>B> = []
for (let let i: numberi = 0; let i: numberi < const as: A[]as.Array<T>.length: numberGets or sets the length of the array. This is a number one higher than the highest index in the array.
length; let i: numberi++) {
const const result: Result.Result<B, X>result = f: (
input: A,
i: number
) => Result.Result<B, X>
const as: A[]as[let i: numberi], let i: numberi)
if (import ResultResult.const isSuccess: <A, E>(
self: Result<A, E>
) => self is Success<A, E>
Checks whether a Result is a Success.
When to use
Use to narrow a known Result to the Success variant.
Details
- Acts as a TypeScript type guard, narrowing to
Success<A, E>
- After narrowing, you can access
.success to read the value
Example (Narrowing to success)
import { Result } from "effect"
const result = Result.succeed(42)
if (Result.isSuccess(result)) {
console.log(result.success)
// Output: 42
}
isSuccess(const result: Result.Result<B, X>result)) {
const out: B[]out.Array<B>.push(...items: B[]): numberAppends new elements to the end of an array, and returns the new length of the array.
push(const result: Result.Success<B, X>const result: {
_tag: "Success";
_op: "Success";
success: 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;
}
Success<B, X>.success: Bsuccess)
}
}
return const out: B[]out
})