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    arrmaybe

    0.2.3 • Public • Published

    ArrMaybe

    Doing FP in Javascript is make believe. This library helps us pretend we have a Maybe type in Native JS by piggy backing on the built in Array type.

    The library is almost entirely static methods except for the included flatMapPolyfill.

    There is some existing and planned interop with static-sum-type.

    The documentation / tests are very light / nonexistent because it's easier to just read the source and see what's going on than to document it.

    Why?

    I find myself writing these helpers all the time, may as well publish/reuse/share them.

    Quick Start

    npm install arrmaybe

    Live Demo

    import * as ArrMaybe from 'arrmaybe'
     
    ArrMaybe.flatMapPolyfill()
     
    const parseJSON = 
        ArrMaybe.safe(JSON.parse)
     
    const get = k => o => 
        ArrMaybe.Just(o).flatMap( 
            o => k in o 
            ? ArrMaybe.Just(o[k]) 
            : ArrMaybe.Nothing() 
        )
     
    const f = s =>
        parseJSON(s)
        .flatMap( get( 'x' ) )
     
    f( '<xml>1</xml>' )
    // => []
     
    f( '{}' )
    // => []
     
    f( '{ "b": 1 }' )
    // => []
     
    f( '{ "x": 1 }' )
    // => [1]

    Static API

    Just

    Wrap a value in a list of one value. This represents what is traditionally called Just or Some in languages like Haskell and Scala.

    Nothing

    Returns an empty list. This represents what is traditionally called Nothing or None.

    flatMapPolyfill

    Mutates Array prototype to have flatMap. A method which is already supported in many modern browsers.

    any

    Accepts a list of Maybe's, and returns a Maybe of a list of values that were not Nothing.

    all

    Accepts a list of Maybe's and returns a Maybe of a list of values if there were no Nothing values in the list.

    Otherwise returns Nothing.

    map

    A static curried version of Array.prototype.map, that doesn't pass in the Array index.

    flatMap

    A static curried version of Array.prototype.flatMap that doesn't pass in the Array index.

    filter

    A static curried version of Array.prototype.filter that doesn't pass in the Array index.

    concat

    Accepts two Maybe values, if both are Just it will execute the concat method on the value inside both Maybe's and wrap the result in a Just, otherwise Nothing.

    alt

    Accepts two Maybe values, if both are Just it will return the first. If only the second is Just it will return the second. Otherwise Nothing.

    justs

    Accepts a list of Maybe's and returns a list of the values that were contained in any Just's within the original list.

    isJust

    Accepts a Maybe, returns true if the Maybe is Just

    isNothing

    Accepts a Maybe, returns true if the Maybe is Nothing

    bifoldType

    Accepts an object with a bifold function. Populates the bifold with Nothing if the left function is called, or Just if the right function is called. Waits for the bifold value to fully apply the function.

    Meant to be used with static-sum-type

    import * as sst from 'static-sum-type'
    import * as Arr from 'arrmaybe'
     
    const Loaded = sst.either('Loaded')
     
    const notLoaded = Loaded.N(55)
    const loaded = Loaded.Y('Hi there')
     
    const f = x => x
        Arr.Just(x)
        .flatMap(
            bifoldType(Loaded)
        )
        .concat('Not loaded yet')
        .slice(0,1)
        .forEach(console.log)
     
    f(notLoaded) // logs: 'Not loaded yet'
    f(loaded) // logs: 'Hi There'

    safe

    Accepts a function, and then a value. Runs the value against the function. If it throws an exception returns Nothing, if it does not, it returns a Just of the return value of the original function.

    Keywords

    none

    Install

    npm i arrmaybe

    DownloadsWeekly Downloads

    1

    Version

    0.2.3

    License

    MIT

    Unpacked Size

    11.1 kB

    Total Files

    5

    Last publish

    Collaborators

    • jaforbes