[Javascript Crocks] Compose Functions for Reusability with the Maybe Type

We can dot-chain our way to great success with an instance of Maybe, but there are probably cases where you need to apply the same series of transformations against different Maybes. In this lesson, we’ll look at some point-free versions of some common Maybe methods and see how we can compose them together to get a reusable function that can be applied to any Maybe instance.

 

We are going to rewrite the following code by using function composion:

const crocks = require('crocks');
const {and, isString, Maybe, prop, safe, option, map, alt, chain} = crocks;
const {not, isEmpty, compose, converge, join, split, toLower} = require('ramda');

///////////////UTILS/////////////////
const joinKey = compose(join('_'),  split(' '), toLower);
const isNotEmpty = compose(
    not,
    isEmpty
)
const isNonEmptyString = and(isNotEmpty, isString);
/*const isNonEmptyString = R.converge(
    R.and,
    [
        isNotEmpty,
        isString
    ]
);*/

const createUrl = key =>`https://egghead.io/articles/${joinKey(key)}`;

////////////////MAIN////////////////

const article = {
     id: 1,
     name: 'Learn FP with this one weird trick'
};

/*
const getUrl = obj =>
    prop('name', obj) // Maybe(string)
        .chain(safe(isNonEmptyString)) // Maybe(string) --safe(isNonEmptyString)--> Maybe(Maybe(String)) --chain--> Maybe(String)
        .alt(Maybe.of('Nope')) // Nothing -> Just('Nope')
        .map(createUrl)
        .option('default');
  */
 
const getSafeName = compose(
    chain(safe(isNonEmptyString)),
    prop('name')
);
const getUrlOrDefault = compose(
    option('Not valid URL'),
    map(createUrl)
);
const getUrl = compose(
    getUrlOrDefault,
    getSafeName
);
const getUrlOrNope = compose(
    getUrlOrDefault,
    alt(Maybe.of('Nope')),
    getSafeName
) 
const res = getUrl(article);
console.log(res);