IO overview
interface IO<A> {
(): A
}
IO<A> represents a non-deterministic synchronous computation that can cause side effects, yields a value of type A and never fails.
If you want to represent a synchronous computation that may fail, please see IOEither. If you want to represent a synchronous computation that may yield nothing, please see IOOption.
Added in v2.0.0
Table of contents
Apply
ap
Apply a function to an argument under a type constructor.
Signature
export declare const ap: <A>(fa: IO<A>) => <B>(fab: IO<(a: A) => B>) => IO<B>
Added in v2.0.0
Functor
map
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) => (fa: IO<A>) => IO<B>
Added in v2.0.0
Monad
chain
Composes computations in sequence, using the return value of one computation to determine the next computation.
Signature
export declare const chain: <A, B>(f: (a: A) => IO<B>) => (ma: IO<A>) => IO<B>
Added in v2.0.0
Pointed
of
Signature
export declare const of: <A>(a: A) => IO<A>
Added in v2.0.0
combinators
apFirst
Combine two effectful actions, keeping only the result of the first.
Derivable from Apply.
Signature
export declare const apFirst: <B>(second: IO<B>) => <A>(first: IO<A>) => IO<A>
Added in v2.0.0
apSecond
Combine two effectful actions, keeping only the result of the second.
Derivable from Apply.
Signature
export declare const apSecond: <B>(second: IO<B>) => <A>(first: IO<A>) => IO<B>
Added in v2.0.0
chainFirst
Composes computations in sequence, using the return value of one computation to determine the next computation and keeping only the result of the first.
Derivable from Chain.
Signature
export declare const chainFirst: <A, B>(f: (a: A) => IO<B>) => (first: IO<A>) => IO<A>
Added in v2.0.0
flap
Derivable from Functor.
Signature
export declare const flap: <A>(a: A) => <B>(fab: IO<(a: A) => B>) => IO<B>
Added in v2.10.0
flatten
Derivable from Chain.
Signature
export declare const flatten: <A>(mma: IO<IO<A>>) => IO<A>
Added in v2.0.0
constructors
fromIO
Signature
export declare const fromIO: <A>(fa: IO<A>) => IO<A>
Added in v2.7.0
instances
Applicative
Signature
export declare const Applicative: Applicative1<'IO'>
Added in v2.7.0
Apply
Signature
export declare const Apply: Apply1<'IO'>
Added in v2.10.0
Chain
Signature
export declare const Chain: Chain1<'IO'>
Added in v2.10.0
ChainRec
Signature
export declare const ChainRec: ChainRec1<'IO'>
Added in v2.7.0
FromIO
Signature
export declare const FromIO: FromIO1<'IO'>
Added in v2.10.0
Functor
Signature
export declare const Functor: Functor1<'IO'>
Added in v2.7.0
Monad
Signature
export declare const Monad: Monad1<'IO'>
Added in v2.7.0
MonadIO
Signature
export declare const MonadIO: MonadIO1<'IO'>
Added in v2.7.0
Pointed
Signature
export declare const Pointed: Pointed1<'IO'>
Added in v2.10.0
URI
Signature
export declare const URI: 'IO'
Added in v2.0.0
URI (type alias)
Signature
export type URI = typeof URI
Added in v2.0.0
getMonoid
Use getApplicativeMonoid instead.
Signature
export declare const getMonoid: <A>(M: Monoid<A>) => Monoid<IO<A>>
Added in v2.0.0
getSemigroup
Use getApplySemigroup instead.
Signature
export declare const getSemigroup: <A>(S: Semigroup<A>) => Semigroup<IO<A>>
Added in v2.0.0
io
This instance is deprecated, use small, specific instances instead. For example if a function needs a Functor instance, pass IO.Functor instead of IO.io (where IO is from import IO from 'fp-ts/IO')
Signature
export declare const io: Monad1<'IO'> & MonadIO1<'IO'> & ChainRec1<'IO'>
Added in v2.0.0
model
IO (interface)
Signature
export interface IO<A> {
(): A
}
Added in v2.0.0
utils
ApT
Signature
export declare const ApT: IO<readonly []>
Added in v2.11.0
Do
Signature
export declare const Do: IO<{}>
Added in v2.9.0
apS
Signature
export declare const apS: <N, A, B>(
name: Exclude<N, keyof A>,
fb: IO<B>
) => (fa: IO<A>) => IO<{ readonly [K in N | keyof A]: K extends keyof A ? A[K] : B }>
Added in v2.8.0
bind
Signature
export declare const bind: <N, A, B>(
name: Exclude<N, keyof A>,
f: (a: A) => IO<B>
) => (ma: IO<A>) => IO<{ readonly [K in N | keyof A]: K extends keyof A ? A[K] : B }>
Added in v2.8.0
bindTo
Signature
export declare const bindTo: <N>(name: N) => <A>(fa: IO<A>) => IO<{ readonly [K in N]: A }>
Added in v2.8.0
let
Signature
export declare const let: <N, A, B>(
name: Exclude<N, keyof A>,
f: (a: A) => B
) => (fa: IO<A>) => IO<{ readonly [K in N | keyof A]: K extends keyof A ? A[K] : B }>
Added in v2.13.0
sequenceArray
Signature
export declare const sequenceArray: <A>(arr: readonly IO<A>[]) => IO<readonly A[]>
Added in v2.9.0
traverseArray
Signature
export declare const traverseArray: <A, B>(f: (a: A) => IO<B>) => (as: readonly A[]) => IO<readonly B[]>
Added in v2.9.0
traverseArrayWithIndex
Signature
export declare const traverseArrayWithIndex: <A, B>(
f: (index: number, a: A) => IO<B>
) => (as: readonly A[]) => IO<readonly B[]>
Added in v2.9.0
traverseReadonlyArrayWithIndex
Equivalent to ReadonlyArray#traverseWithIndex(Applicative).
Signature
export declare const traverseReadonlyArrayWithIndex: <A, B>(
f: (index: number, a: A) => IO<B>
) => (as: readonly A[]) => IO<readonly B[]>
Added in v2.11.0
traverseReadonlyNonEmptyArrayWithIndex
Equivalent to ReadonlyNonEmptyArray#traverseWithIndex(Applicative).
Signature
export declare const traverseReadonlyNonEmptyArrayWithIndex: <A, B>(
f: (index: number, a: A) => IO<B>
) => (as: ReadonlyNonEmptyArray<A>) => IO<ReadonlyNonEmptyArray<B>>
Added in v2.11.0