@sweet-monads/interfaces
Collection of interfaces which describe functional programming abstractions.
This library belongs to sweet-monads project
sweet-monads — easy-to-use monads implementation with static types definition and separated packages.
- No dependencies, one small file
- Easily auditable TypeScript/JS code
- Check out all libraries: either, iterator, interfaces, maybe identity
Usage
npm install @sweet-monads/interfaces
import { Functor } from "@sweet-monads/interfaces";
class MyClass<T> implements Functor<T> {
map<A>(fn: (i: T) => A): MyClass<A> {
return new MyClass<A>();
}
}Available Interfaces
Functor
https://wiki.haskell.org/Functor
An abstract datatype Functor<A>, which has the ability for it's value(s) to be mapped over can become an instance of the Functor interface. That is to say, a new Functor, Functor<B> can be made from Functor<A> by transforming all of it's value(s), whilst leaving the structure of f itself unmodified.
Functors are required to obey certain laws in regards to their mapping. Ensuring instances of Functor obey these laws means the behaviour of fmap remains predictable.
Methods:
Functor#map
function map<A, B>(f: (x: A) => B): Functor<B>;Minimal Complete Definition
map<A, B>(f: (x: A) => B): Functor<B>;Functor Laws
Functors must preserve identity morphisms
const f = new SomeFunctorImplementation(); // for all functors
const id = x => x;
expect(f.map(id)).toEqual(f);Functors preserve composition of morphisms
declare function twice(x: number): number; // for all functions
declare function toString(x: number): string; // for all functions
const f = new SomeFunctorImplementation<number>();
expect(f.map(x => toString(twice(x)))).toEqual(f.map(twice).map(toString));AsyncFunctor
Async version of Functor, which provides async version of the map method.
Methods:
AsyncFunctor#asyncMap
function asyncMap<A, B>(f: (x: A) => Promise<B>): Promise<AsyncFunctor<B>>;Minimal Complete Definition
Functor implementation.
asyncMap<A, B>(f: (x: A) => Promise<B>): Promise<AsyncFunctor<B>>;AsyncFunctor Laws
All the Functor Laws should be applied to the async version, so:
AsyncFunctors must preserve identity morphisms
const f = new SomeAsyncFunctorImplementation(); // for all functors
const id = x => Promise.resolve(x);
expect(await f.asyncMap(id)).toEqual(f);AsyncFunctors preserve composition of morphisms
declare function twice(x: number): Promise<number>; // for all functions
declare function toString(x: number): Promise<string>; // for all functions
Promise.resolve(toString(twice(x)))
const f = new SomeAsyncFunctorImplementation<number>();
expect(await f.asyncMap(x => twice(x).then(toString))).toEqual(await f.asyncMap(twice).then(f => f.asyncMap(toString)));Alternative
https://en.wikibooks.org/wiki/Haskell/Alternative_and_MonadPlus
Several classes (Applicative, Monad) have "monoidal" subclasses, intended to model computations that support "failure" and "choice" (in some appropriate sense).
The basic intuition is that empty represents some sort of "failure", and or represents a choice between alternatives. (However, this intuition does not fully capture the nuance possible; see the section on Laws below.) Of course, or should be associative and empty should be the identity element for it. Instances of Alternative must implement empty and or; some and many have default implementations but are included in the class since specialized implementations may be more efficient than the default.
Current implementation is not fully port of Alternative from Haskell, because we don't make the interface an child interface of Applicative and dropped empty static member for ability to implement Alternative for classes like Either.
Methods:
Alternative#or
function or<T>(arg: Alternative<T>): Alternative<T>;Applicative
https://wiki.haskell.org/Applicative_functor
This module describes a structure intermediate between a functor and a monad (technically, a strong lax monoidal functor). Compared with monads, this interface lacks the full power of the binding operation chain.
Methods:
Applicative.from
function from<A>(x: A): Applicative<A>;Applicative#apply
function apply<A, B>(this: Applicative<(a: A) => B>, arg: Applicative<A>): Applicative<B>;
function apply<A, B>(this: Applicative<A>, fn: Applicative<(a: A) => B>): Applicative<B>;Minimal Complete Definition
Functor implementation.
static from<A>(x: A): Applicative<A>;apply<A, B>(this: Applicative<(a: A) => B>, arg: Applicative<A>): Applicative<B>;
apply<A, B>(this: Applicative<A>, fn: Applicative<(a: A) => B>): Applicative<B>;Applicative Laws
Identity Law
declare var x: Applicative<unknown>;
const id = x => x;
expect(SomeApplicative.from(id).apply(x)).toEqual(x);Homomorphism Law
declare var x: unknown;
declare var f: (x: unknown) => unknown;
expect(SomeApplicative.from(f).apply(x)).toEqual(SomeApplicative.from(f(x)));AsyncApplicative
Async version of Applicative, which provides async version of the apply method.
Methods:
AsyncApplicative#asyncApply
function asyncApply<A, B>(this: AsyncApplicative<(a: A) => Promise<B>>, arg: AsyncApplicative<Promise<A> | A>): Promise<AsyncApplicative<B>>;
function asyncApply<A, B>(this: AsyncApplicative<Promise<A> | A>, fn: AsyncApplicative<(a: A) => Promise<B>>): Promise<AsyncApplicative<B>>;Minimal Complete Definition
Applicative implementation.
AsyncFunctor implementation.
asyncApply<A, B>(this: AsyncApplicative<(a: A) => Promise<B>>, arg: AsyncApplicative<Promise<A> | A>): Promise<AsyncApplicative<B>>;
asyncApply<A, B>(this: AsyncApplicative<Promise<A> | A>, fn: AsyncApplicative<(a: A) => Promise<B>>): Promise<AsyncApplicative<B>>;AsyncApplicative Laws
All the Applicative Laws should be applied to the async version, so:
Identity Law
declare var x: AsyncApplicative<unknown>;
const id = x => Promise.resolve(x);
expect(await SomeAsyncApplicative.from(id).asyncApply(x)).toEqual(x);Homomorphism Law
declare var x: unknown;
declare var f: (x: unknown) => Promise<unknown>;
expect(await SomeAsyncApplicative.from(f).asyncApply(x)).toEqual(SomeAsyncApplicative.from(await f(x)));Monad
https://wiki.haskell.org/Monad
Monads can be thought of as composable computation descriptions. The essence of monad is thus separation of composition timeline from the composed computation's execution timeline, as well as the ability of computation to implicitly carry extra data, as pertaining to the computation itself, in addition to its one (hence the name) output, that it will produce when run (or queried, or called upon). This lends monads to supplementing pure calculations with features like I/O, common environment, updatable state, etc.
Methods:
Monad#chain
function chain<A, B>(f: (x: A) => Monad<B>): Monad<B>;Monad#join
function join<T>(this: Monad<Monad<T>>): Monad<T>;Minimal Complete Definition
Applicative implementation.
chain<A, B>(f: (x: A) => Monad<B>): Monad<B>;
join<T>(this: Monad<Monad<T>>): Monad<T>;Monad Laws
Left identity Law
declare var x: unknown;
declare function f(x: unknown): Monad<unknown>;
expect(SomeMonad.from(x).chain(f)).toEqual(f(x));Right identity Law
declare var mx: Monad<unknown>;
declare function f(x: unknown): Monad<unknown>;
expect(mx.chain(SomeMonad.from)).toEqual(mx);Associativity Law
declare var mx: Monad<unknown>;
declare function f(x: unknown): Monad<unknown>;
declare function g(x: unknown): Monad<unknown>;
expect(mx.chain(x => f(x).chain(g))).toEqual(mx.chain(f).chain(g));AsyncMonad
Async version of Monad, which provides async version of the chain method.
Methods:
Monad#chain
function asyncChain<A, B>(f: (x: A) => Promise<AsyncMonad<B>>): Promise<AsyncMonad<B>>;Minimal Complete Definition
Monad implementation.
AsyncApplicative implementation.
asyncChain<A, B>(f: (x: A) => Promise<AsyncMonad<B>>): Promise<Monad<B>>;AsyncMonad Laws
All the Monad Laws should be applied to the async version, so:
Left identity Law
declare var x: unknown;
declare function f(x: unknown): Promise<AsyncMonad<unknown>>;
expect(await SomeAsyncMonad.from(x).asyncChain(f)).toEqual(await f(x));Right identity Law
declare var mx: AsyncMonad<unknown>;
declare function f(x: unknown): Promise<AsyncMonad<unknown>>;
expect(await mx.asyncChain(x => Promise.resolve(SomeAsyncMonad.from(x)))).toEqual(mx);Associativity Law
declare var ax: AsyncMonad<unknown>;
declare function f(x: unknown): Promise<AsyncMonad<unknown>>;
declare function g(x: unknown): Promise<AsyncMonad<unknown>>;
expect(await ax.asyncChain(x => f(x).then(fx => fx.asyncChain(g)))).toEqual(await ax.asyncChain(f).then(fx => fx.asyncChain(g)));AsyncChainable
Static interface which give an ability to use AsyncMonad more comfortable with Promise.
Should be used with
ClassImplementsdecorator
Methods:
AsyncChainable<M>#chain
function chain<A, B>(f: (v: A) => Promise<M & AsyncMonad<B>>): (m: M & AsyncMonad<A>) => Promise<M & AsyncMonad<B>>;Usage
@ClassImplements<IdentityMonad<unknown>>
class IdentityMonad<T> extends AsyncMonad<T> { /*...*/ }
declare function getAsyncValue(): Promise<IdentityMonad<number>>
declare function sendToServer(value: number): Promise<IdentityMonad<void>>
const value = await getAsyncValue().then(chain(sendToServer));Container
Is a value wrapper, that allows to get value (if state of the container is valid), or throws error if not.
Methods:
Container#unwrap
const lucky = Math.random() > 0.5 ? just(":)") : none();
// Will either return ":)" or throw an error
lucky.unwrap();License
MIT (c) Artem Kobzar see LICENSE file.