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The ApplicativeError type class is a Applicative that also allows you to raise and or handle an error value.

This type class allows one to abstract over error-handling applicative types.

MUST follow the law defined in ApplicativeErrorLaws.

Implementation notes

Even though in TypeScript the Funfix library is using abstract class to express type classes, when implementing this type class it is recommended that you implement it as a mixin using "implements", instead of extending it directly with "extends". See TypeScript: Mixins for details and note that we already have applyMixins defined.

Implementation example:

import {
  HK,
  ApplicativeError,
  registerTypeClassInstance,
  applyMixins,
  Try
} from "funfix"

// Type alias defined for readability.
// HK is our encoding for higher-kinded types.
type BoxK<T> = HK<Box<any>, T>

class Box<T> implements HK<Box<any>, T> {
  constructor(public value: Try<T>) {}

  // Implements HK<Box<any>, A>, not really needed, but useful in order
  // to avoid type casts. Note they can and should be undefined:
  readonly _funKindF: Box<any>
  readonly _funKindA: T
}

class BoxApplicativeError implements ApplicativeError<Box<any>, any> {
  pure<A>(a: A): Box<A> { return new Box(Try.success(a)) }

  ap<A, B>(fa: BoxK<A>, ff: BoxK<(a: A) => B>): Box<B> {
    const ta = (fa as Box<A>).value
    const tf = (ff as Box<(a: A) => B>).value
    return new Box(Try.map2(ta, tf, (a, f) => f(a)))
  }

  raise<A>(e: any): HK<Box<any>, A> {
    return new Box(Try.failure(e))
  }

  recoverWith<A>(fa: BoxK<A>, f: (e: any) => BoxK<A>): HK<Box<any>, A> {
    return new Box((fa as Box<A>).value.recoverWith(e => (f(e) as Box<A>).value))
  }

  // Mixed-in, as these have default implementations
  map: <A, B>(fa: BoxK<A>, f: (a: A) => B) => Box<B>
  map2: <A, B, Z>(fa: BoxK<A>, fb: BoxK<B>, f: (a: A, b: B) => Z) => Box<Z>
  product: <A, B> (fa: BoxK<A>, fb: BoxK<B>) => Box<[A, B]>
  unit: () => Box<void>
  recover: <A>(fa: HK<Box<any>, A>, f: (e: any) => A) => HK<Box<any>, A>
  attempt: <A>(fa: HK<Box<any>, A>) => HK<Box<any>, Either<any, A>>
}

// Call needed in order to implement `map`, `map2`, `product`, etc.
// using the default implementations defined by `ApplicativeError`,
// because we are using `implements` instead of `extends` above and
// because in this sample we want the default implementations,
// but note that you can always provide your own
applyMixins(BoxApplicativeError, [ApplicativeError])

// Registering global ApplicativeError instance for Box, needed in order
// for the `functorOf(Box)`, `applyOf(Box)`, `applicativeOf(Box)`
// and `applicativeErrorOf(Box)` calls to work
registerTypeClassInstance(ApplicativeError)(Box, new BoxApplicativeError())

We are using implements in order to support multiple inheritance and to avoid inheriting any static members. In the Flow definitions (e.g. .js.flow files) for Funfix these type classes are defined with "interface", as they are meant to be interfaces that sometimes have default implementations and not classes.

Credits

This type class is inspired by the equivalent in Haskell's standard library and the implementation is inspired by the Typelevel Cats project.

Type parameters

  • F

  • E

Hierarchy

  • ApplicativeError

Implements

Implemented by

Index

Properties

map

map: function

Mixed-in from Applicative.map.

Type declaration

    • <A, B>(fa: HK<F, A>, f: function): HK<F, B>
    • Type parameters

      • A

      • B

      Parameters

      • fa: HK<F, A>
      • f: function
          • (a: A): B
          • Parameters

            • a: A

            Returns B

      Returns HK<F, B>

map2

map2: function

Mixed-in from Apply.map2.

Type declaration

    • <A, B, Z>(fa: HK<F, A>, fb: HK<F, B>, f: function): HK<F, Z>
    • Type parameters

      • A

      • B

      • Z

      Parameters

      • fa: HK<F, A>
      • fb: HK<F, B>
      • f: function
          • (a: A, b: B): Z
          • Parameters

            • a: A
            • b: B

            Returns Z

      Returns HK<F, Z>

product

product: function

Mixed-in from Apply.product.

Type declaration

    • <A, B>(fa: HK<F, A>, fb: HK<F, B>): HK<F, [A, B]>
    • Type parameters

      • A

      • B

      Parameters

      • fa: HK<F, A>
      • fb: HK<F, B>

      Returns HK<F, [A, B]>

unit

unit: function

Mixed-in from Applicative.unit.

Type declaration

    • (): HK<F, void>
    • Returns HK<F, void>

Methods

ap

  • ap<A, B>(fa: HK<F, A>, ff: HK<F, function>): HK<F, B>

attempt

  • attempt<A>(fa: HK<F, A>): HK<F, Either<E, A>>
  • Handle errors by turning them into Either values.

    If there is no error, then a Right value will be returned. All non-fatal errors should be handled by this method.

    Type parameters

    • A

    Parameters

    • fa: HK<F, A>

    Returns HK<F, Either<E, A>>

pure

  • pure<A>(a: A): HK<F, A>

raise

  • raise<A>(e: E): HK<F, A>
  • Lift an error into the F context.

    Type parameters

    • A

    Parameters

    • e: E

    Returns HK<F, A>

recover

  • recover<A>(fa: HK<F, A>, f: function): HK<F, A>
  • Handle any error by mapping it to an A value.

    see

    recoverWith to map to an F[A] value instead of simply an A value.

    Type parameters

    • A

    Parameters

    • fa: HK<F, A>
    • f: function
        • (e: E): A
        • Parameters

          • e: E

          Returns A

    Returns HK<F, A>

recoverWith

  • recoverWith<A>(fa: HK<F, A>, f: function): HK<F, A>
  • Handle any error, potentially recovering from it, by mapping it to an F<A> value.

    see

    recover to handle any error by simply mapping it to an A value instead of an F<A>.

    Type parameters

    • A

    Parameters

    • fa: HK<F, A>
    • f: function
        • (e: E): HK<F, A>
        • Parameters

          • e: E

          Returns HK<F, A>

    Returns HK<F, A>

Legend

  • Module
  • Object literal
  • Variable
  • Function
  • Function with type parameter
  • Index signature
  • Type alias
  • Enumeration
  • Enumeration member
  • Property
  • Method
  • Interface
  • Interface with type parameter
  • Constructor
  • Property
  • Method
  • Index signature
  • Class
  • Class with type parameter
  • Constructor
  • Property
  • Method
  • Accessor
  • Index signature
  • Inherited constructor
  • Inherited property
  • Inherited method
  • Inherited accessor
  • Protected property
  • Protected method
  • Protected accessor
  • Private property
  • Private method
  • Private accessor
  • Static property
  • Static method

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