A data structure providing "inclusive-or" as opposed to Either
's "exclusive-or".
If you interpret Either<E, A>
as suggesting the computation may either fail or succeed (exclusively), then
These<E, A>
may fail, succeed, or do both at the same time.
There are a few ways to interpret the both case:
Another way you can think of These<E, A>
is saying that we want to handle E
kind of data, A
kind of data, or
both E
and A
kind of data at the same time. This is particularly useful when it comes to displaying UI's.
(description adapted from https://package.elm-lang.org/packages/joneshf/elm-these)
Adapted from https://github.com/purescript-contrib/purescript-these
Added in v2.0.0
Map a pair of functions over the two type arguments of the bifunctor.
Signature
export declare const bimap: <E, G, A, B>(f: (e: E) => G, g: (a: A) => B) => (fa: These<E, A>) => These<G, B>
Added in v2.0.0
Map a function over the first type argument of a bifunctor.
Signature
export declare const mapLeft: <E, G>(f: (e: E) => G) => <A>(fa: These<E, A>) => These<G, A>
Added in v2.0.0
Signature
export declare const foldMap: <M>(M: Monoid<M>) => <A>(f: (a: A) => M) => <E>(fa: These<E, A>) => M
Added in v2.0.0
Signature
export declare const reduce: <A, B>(b: B, f: (b: B, a: A) => B) => <E>(fa: These<E, A>) => B
Added in v2.0.0
Signature
export declare const reduceRight: <A, B>(b: B, f: (a: A, b: B) => B) => <E>(fa: These<E, A>) => B
Added in v2.0.0
map
can be used to turn functions (a: A) => B
into functions (fa: F<A>) => F<B>
whose argument and return types
use the type constructor F
to represent some computational context.
Signature
export declare const map: <A, B>(f: (a: A) => B) => <E>(fa: These<E, A>) => These<E, B>
Added in v2.0.0
Signature
export declare const swap: <E, A>(fa: These<E, A>) => These<A, E>
Added in v2.4.0
Signature
export declare function both<E, A>(left: E, right: A): These<E, A>
Added in v2.0.0
Takes a pair of Option
s and attempts to create a These
from them
Signature
export declare function fromOptions<E, A>(fe: Option<E>, fa: Option<A>): Option<These<E, A>>
Example
import { fromOptions, left, right, both } from 'fp-ts/These'
import { none, some } from 'fp-ts/Option'
assert.deepStrictEqual(fromOptions(none, none), none)
assert.deepStrictEqual(fromOptions(some('a'), none), some(left('a')))
assert.deepStrictEqual(fromOptions(none, some(1)), some(right(1)))
assert.deepStrictEqual(fromOptions(some('a'), some(1)), some(both('a', 1)))
Added in v2.0.0
Signature
export declare function left<E = never, A = never>(left: E): These<E, A>
Added in v2.0.0
Signature
export declare function leftOrBoth<E>(e: E): <A>(ma: Option<A>) => These<E, A>
Example
import { leftOrBoth, left, both } from 'fp-ts/These'
import { none, some } from 'fp-ts/Option'
assert.deepStrictEqual(leftOrBoth('a')(none), left('a'))
assert.deepStrictEqual(leftOrBoth('a')(some(1)), both('a', 1))
Added in v2.0.0
Signature
export declare function right<E = never, A = never>(right: A): These<E, A>
Added in v2.0.0
Signature
export declare function rightOrBoth<A>(a: A): <E>(me: Option<E>) => These<E, A>
Example
import { rightOrBoth, right, both } from 'fp-ts/These'
import { none, some } from 'fp-ts/Option'
assert.deepStrictEqual(rightOrBoth(1)(none), right(1))
assert.deepStrictEqual(rightOrBoth(1)(some('a')), both('a', 1))
Added in v2.0.0
Signature
export declare function fold<E, A, B>(
onLeft: (e: E) => B,
onRight: (a: A) => B,
onBoth: (e: E, a: A) => B
): (fa: These<E, A>) => B
Added in v2.0.0
Returns an E
value if possible
Signature
export declare function getLeft<E, A>(fa: These<E, A>): Option<E>
Example
import { getLeft, left, right, both } from 'fp-ts/These'
import { none, some } from 'fp-ts/Option'
assert.deepStrictEqual(getLeft(left('a')), some('a'))
assert.deepStrictEqual(getLeft(right(1)), none)
assert.deepStrictEqual(getLeft(both('a', 1)), some('a'))
Added in v2.0.0
Returns the E
value if and only if the value is constructed with Left
Signature
export declare function getLeftOnly<E, A>(fa: These<E, A>): Option<E>
Example
import { getLeftOnly, left, right, both } from 'fp-ts/These'
import { none, some } from 'fp-ts/Option'
assert.deepStrictEqual(getLeftOnly(left('a')), some('a'))
assert.deepStrictEqual(getLeftOnly(right(1)), none)
assert.deepStrictEqual(getLeftOnly(both('a', 1)), none)
Added in v2.0.0
Returns an A
value if possible
Signature
export declare function getRight<E, A>(fa: These<E, A>): Option<A>
Example
import { getRight, left, right, both } from 'fp-ts/These'
import { none, some } from 'fp-ts/Option'
assert.deepStrictEqual(getRight(left('a')), none)
assert.deepStrictEqual(getRight(right(1)), some(1))
assert.deepStrictEqual(getRight(both('a', 1)), some(1))
Added in v2.0.0
Returns the A
value if and only if the value is constructed with Right
Signature
export declare function getRightOnly<E, A>(fa: These<E, A>): Option<A>
Example
import { getRightOnly, left, right, both } from 'fp-ts/These'
import { none, some } from 'fp-ts/Option'
assert.deepStrictEqual(getRightOnly(left('a')), none)
assert.deepStrictEqual(getRightOnly(right(1)), some(1))
assert.deepStrictEqual(getRightOnly(both('a', 1)), none)
Added in v2.0.0
Signature
export declare function toTuple<E, A>(e: E, a: A): (fa: These<E, A>) => [E, A]
Example
import { toTuple, left, right, both } from 'fp-ts/These'
assert.deepStrictEqual(toTuple('a', 1)(left('b')), ['b', 1])
assert.deepStrictEqual(toTuple('a', 1)(right(2)), ['a', 2])
assert.deepStrictEqual(toTuple('a', 1)(both('b', 2)), ['b', 2])
Added in v2.0.0
Returns true
if the these is an instance of Both
, false
otherwise
Signature
export declare function isBoth<E, A>(fa: These<E, A>): fa is Both<E, A>
Added in v2.0.0
Returns true
if the these is an instance of Left
, false
otherwise
Signature
export declare function isLeft<E, A>(fa: These<E, A>): fa is Left<E>
Added in v2.0.0
Returns true
if the these is an instance of Right
, false
otherwise
Signature
export declare function isRight<E, A>(fa: These<E, A>): fa is Right<A>
Added in v2.0.0
Signature
export declare const Bifunctor: Bifunctor2<'These'>
Added in v2.7.0
Signature
export declare const Foldable: Foldable2<'These'>
Added in v2.7.0
Signature
export declare const Functor: Functor2<'These'>
Added in v2.7.0
Signature
export declare const Traversable: Traversable2<'These'>
Added in v2.7.0
Signature
export declare const URI: 'These'
Added in v2.0.0
Signature
export type URI = typeof URI
Added in v2.0.0
Signature
export declare function getApplicative<E>(SE: Semigroup<E>): Applicative2C<URI, E>
Added in v2.7.0
Signature
export declare function getEq<E, A>(EE: Eq<E>, EA: Eq<A>): Eq<These<E, A>>
Added in v2.0.0
Signature
export declare function getMonad<E>(SE: Semigroup<E>): Monad2C<URI, E> & MonadThrow2C<URI, E>
Added in v2.0.0
Signature
export declare function getSemigroup<E, A>(SE: Semigroup<E>, SA: Semigroup<A>): Semigroup<These<E, A>>
Added in v2.0.0
Signature
export declare function getShow<E, A>(SE: Show<E>, SA: Show<A>): Show<These<E, A>>
Added in v2.0.0
Signature
export declare const these: Functor2<'These'> & Bifunctor2<'These'> & Foldable2<'These'> & Traversable2<'These'>
Added in v2.0.0
Signature
export interface Both<E, A> {
readonly _tag: 'Both'
readonly left: E
readonly right: A
}
Added in v2.0.0
Signature
export type These<E, A> = Either<E, A> | Both<E, A>
Added in v2.0.0
Signature
export declare const sequence: Sequence2<'These'>
Added in v2.6.3
Signature
export declare const traverse: PipeableTraverse2<'These'>
Added in v2.6.3