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This library is no longer maintained!

If you're reading this, you likely use lemons.js in combination with decoders. In decoders >= 2.0, lemons is no longer a dependency, and there is no furhter wide-spread use of it. I've archived the repo to make clear it's no longer maintained.

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🍋 Common algebraïc data types for JavaScript, 'cause when life hands you lemons...

Maybe

Pseudo-type:

type Maybe<T>
    = Just T
    | Nothing

Usage example:

import Maybe, { Just, Nothing } from 'lemons/Maybe';
// or: import { Maybe, Just, Nothing } from 'lemons';

const r1: Maybe<number> = Just(42);
r1.isJust()         // => true
r1.isNothing()      // => false
r1.withDefault(99)  // => 42
r1.unwrap()         // => 42
r1.expect('Foo')    // => 42

const r2: Maybe<number> = Nothing();
r2.isJust()         // => false
r2.isNothing()      // => true
r2.withDefault(99)  // => 99
r2.unwrap()         // throws Error('Cannot unwrap a Nothing')
r2.expect('Foo')    // throws Error('Foo')

Result

Pseudo-type:

type Result<E, T>
    = Ok T
    | Err E

Usage example:

import Result, { Ok, Err } from 'lemons/Result';
// or: import { Result, Ok, Err } from 'lemons';

const r1: Result<string, number> = Ok(42);
r1.isOk()           // => true
r1.isErr()          // => false
r1.withDefault(99)  // => 42
r1.unwrap()         // => 42

const r2: Result<string, number> = Err('Oops');
r2.isOk()           // => false
r2.isErr()          // => true
r2.withDefault(99)  // => 99
r2.unwrap()         // throws 'Oops'

LazyResult

Pseudo-type:

type LazyResult<E, T>
    = Initial
    | Loading
    | Failure E
    | Success T

Useful for state management that typically has an initial, loading, and a failure/success outcome state, like page loading, or submitting a form. The following example shows how you would use the LazyResult as part of a React app, but since ADTs are simple data structures, they work with any technology.

Annotated usage example: