README.md

es6-monads

Playing around with the monads Maybe and Either and their functors Just, Nothing, Left and Right. This might help to prevent bugs during runtime. As some of you might already guess, this is inspired by Erlang and Elm ;)

Playing around with it:

// Using require instead of import, because it is supported in
// my atom editor with the script plugin, which allows me
// to simply press cmd i to run all of this without babel etc
const Maybe = require('./Maybe.js')
const Either = require('./Either.js')

// some random functions, which are not important
// and are just here to play around with them below
const times = nums => nums.reduce((a, b) => a * b, 1)
const double = a => a * 2
const quarter = a => a / 4
const pretty = a => `The value is ${a}!`

// Composing the functions together
const timesDoubleQuarterPretty = arr => 
    Maybe(times(arr))
        .fmap(double)
        .fmap(quarter)
        .fmap(pretty)

// Imagine because of some bug our input array is broken,
// but the code still runs fine, the Maybe returned a Nothing wrapper
const broken = [1, 2, 'x', 3, 4]
const result1 = timesDoubleQuarterPretty(broken) // Nothing

// The second input array is intact and the Maybe returns a Just wrapper
const intact = [1, 2, 3, 4]
const result2 = timesDoubleQuarterPretty(intact) // Just 'The value is 12!'

// And here we can simply use Either to pick the valid one
// Either returns the Left or Right functor which both have the .value method
const result = Either(result1, result2) // Right 'The value is 12!'
result.value() // 'The value is 12!'

I would love feedback! Please tell me if I'm not correctly understanding this stuff by writing an issue or sending me a tweet @KimHogeling