<A, Pass, Fail>(self: Filter<A, Pass, Fail>): (
input: A
) => Option.Option<Pass>Converts a Filter into a function that returns Some for passed values
and None for filtered-out values.
When to use
Use when adapting a Filter to Option-based code where passed values
become Some and filtered-out inputs become None.
export const const toOption: <A, Pass, Fail>(
self: Filter<A, Pass, Fail>
) => (input: A) => Option.Option<Pass>
Converts a Filter into a function that returns Some for passed values
and None for filtered-out values.
When to use
Use when adapting a Filter to Option-based code where passed values
become Some and filtered-out inputs become None.
toOption = <function (type parameter) A in <A, Pass, Fail>(self: Filter<A, Pass, Fail>): (input: A) => Option.Option<Pass>A, function (type parameter) Pass in <A, Pass, Fail>(self: Filter<A, Pass, Fail>): (input: A) => Option.Option<Pass>Pass, function (type parameter) Fail in <A, Pass, Fail>(self: Filter<A, Pass, Fail>): (input: A) => Option.Option<Pass>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) => Option.Option<Pass>A, function (type parameter) Pass in <A, Pass, Fail>(self: Filter<A, Pass, Fail>): (input: A) => Option.Option<Pass>Pass, function (type parameter) Fail in <A, Pass, Fail>(self: Filter<A, Pass, Fail>): (input: A) => Option.Option<Pass>Fail>
): (input: Ainput: function (type parameter) A in <A, Pass, Fail>(self: Filter<A, Pass, Fail>): (input: A) => Option.Option<Pass>A) => 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) Pass in <A, Pass, Fail>(self: Filter<A, Pass, Fail>): (input: A) => Option.Option<Pass>Pass> =>
(input: Ainput: function (type parameter) A in <A, Pass, Fail>(self: Filter<A, Pass, Fail>): (input: A) => Option.Option<Pass>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 OptionOption.const none: <A = never>() => Option<A>Creates an Option representing the absence of a value.
When to use
Use to represent a missing or uninitialized value, such as returning "no
result" from a function.
Details
- Returns
Option<never>, which is a subtype of Option<A> for any A
- Always returns the same singleton instance
Example (Creating an empty Option)
import { Option } from "effect"
// ┌─── Option<never>
// ▼
const noValue = Option.none()
console.log(noValue)
// Output: { _id: 'Option', _tag: 'None' }
none() : import OptionOption.const some: <A>(value: A) => Option<A>Wraps the given value into an Option to represent its presence.
When to use
Use to wrap a known present value as Option
- Returning a successful result from a partial function
Details
- Always returns
Some<A>
- Does not filter
null or undefined; use
fromNullishOr
for that
Example (Wrapping a value)
import { Option } from "effect"
// ┌─── Option<number>
// ▼
const value = Option.some(1)
console.log(value)
// Output: { _id: 'Option', _tag: 'Some', value: 1 }
some(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)
}