<A, Pass, Fail>(self: Filter<A, Pass, Fail>): (
input: A
) => Result.Result<Pass, Fail>Converts a Filter into a function that returns the underlying
Result.Result for each input.
When to use
Use to adapt a Filter to APIs that expect a plain function returning
Result, while preserving both the pass value and the failure value.
export const const toResult: <A, Pass, Fail>(
self: Filter<A, Pass, Fail>
) => (input: A) => Result.Result<Pass, Fail>
Converts a Filter into a function that returns the underlying
Result.Result for each input.
When to use
Use to adapt a Filter to APIs that expect a plain function returning
Result, while preserving both the pass value and the failure value.
toResult = <function (type parameter) A in <A, Pass, Fail>(self: Filter<A, Pass, Fail>): (input: A) => Result.Result<Pass, Fail>A, function (type parameter) Pass in <A, Pass, Fail>(self: Filter<A, Pass, Fail>): (input: A) => Result.Result<Pass, Fail>Pass, function (type parameter) Fail in <A, Pass, Fail>(self: Filter<A, Pass, Fail>): (input: A) => Result.Result<Pass, Fail>Fail>(
self: Filter<A, Pass, Fail>self: interface Filter<in Input, out Pass = Input, out Fail = Input>Represents a filter function that can transform inputs to outputs or filter them out.
Details
A filter takes an input value and either returns a boxed pass value or the
special fail type to indicate the value should be filtered out.
Example (Defining a positive number filter)
import { Filter, Result } from "effect"
// A filter that only passes positive numbers
const positiveFilter: Filter.Filter<number> = (n) => n > 0 ? Result.succeed(n) : Result.fail(n)
console.log(positiveFilter(5)) // Result.succeed(5)
console.log(positiveFilter(-3)) // Result.fail(-3)
Filter<function (type parameter) A in <A, Pass, Fail>(self: Filter<A, Pass, Fail>): (input: A) => Result.Result<Pass, Fail>A, function (type parameter) Pass in <A, Pass, Fail>(self: Filter<A, Pass, Fail>): (input: A) => Result.Result<Pass, Fail>Pass, function (type parameter) Fail in <A, Pass, Fail>(self: Filter<A, Pass, Fail>): (input: A) => Result.Result<Pass, Fail>Fail>
): (input: Ainput: function (type parameter) A in <A, Pass, Fail>(self: Filter<A, Pass, Fail>): (input: A) => Result.Result<Pass, Fail>A) => 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) Pass in <A, Pass, Fail>(self: Filter<A, Pass, Fail>): (input: A) => Result.Result<Pass, Fail>Pass, function (type parameter) Fail in <A, Pass, Fail>(self: Filter<A, Pass, Fail>): (input: A) => Result.Result<Pass, Fail>Fail> =>
(input: Ainput: function (type parameter) A in <A, Pass, Fail>(self: Filter<A, Pass, Fail>): (input: A) => Result.Result<Pass, Fail>A) => {
const const result: Result.Result<Pass, Fail>result = self: Filter<A, Pass, Fail>self(input: Ainput)
return import ResultResult.const isFailure: <A, E>(
self: Result<A, E>
) => self is Failure<A, E>
Checks whether a Result is a Failure.
When to use
Use to narrow a known Result to the Failure variant.
Details
- Acts as a TypeScript type guard, narrowing to
Failure<A, E>
- After narrowing, you can access
.failure to read the error value
Example (Narrowing to failure)
import { Result } from "effect"
const result = Result.fail("oops")
if (Result.isFailure(result)) {
console.log(result.failure)
// Output: "oops"
}
isFailure(const result: Result.Result<Pass, Fail>result) ? import ResultResult.const fail: <E>(
left: E
) => Result<never, E>
Creates a Result holding a Failure value.
When to use
Use to represent a failed Result with a typed failure value.
Details
- The success type
A defaults to never
Example (Creating a failure)
import { Result } from "effect"
const result = Result.fail("Something went wrong")
console.log(Result.isFailure(result))
// Output: true
fail(const result: Result.Failure<Pass, Fail>const result: {
_tag: "Failure";
_op: "Failure";
failure: 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;
}
Failure<Pass, Fail>.failure: Failfailure) : import ResultResult.const succeed: <A>(right: A) => Result<A>Creates a Result holding a Success value.
Details
- Use when you have a value and want to lift it into the
Result type
- The error type
E defaults to never
Example (Wrapping a value)
import { Result } from "effect"
const result = Result.succeed(42)
console.log(Result.isSuccess(result))
// Output: true
succeed(const result: Result.Success<Pass, Fail>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<Pass, Fail>.success: Passsuccess)
}