inflection.js

// Let's learn higher order functions, currying, and partial application
// with a simple, yet useful example

// It's a nice UI touch is to dynamically change a word in a phrase from
// singular to plural based on the quantity of that item

// 4 cats
// 0 dogs
// 1 human
 
// I call this an "inflection", and like to write this simple helper
// function in my apps

const inflect = singular => plural => quantity => quantity === 1 ? singular : plural

// A higher order function either recieves a function as an argument,
// returns a function, or both. We have a higher order function here,
// because we are returning a new function after each argument.

// A curried function only receives one argument at a time (instead of all
// of them at once). This allows us to "partially apply" values to the
// returned functions

// Partial application is when a function already has a value applied
// because of a closure.

// What does this return? 
const humanInflection = inflect('human')('humans') 

// It returns this function:
((quantity) => quantity === 1 ? 'human' : 'humans')
// And I can use it over and over again with whatever `quantity` I give it

// I can make other inflections
const indexInflection = inflect('index')('indices')
const datumInflection = inflect('datum')('data')

// And I can use them wherever I want

`I met ${humanQuantity} ${humanInflection(humanQuantity)} today.`

`The array has ${array.length} ${indexInflection(array.length)}`

`I have looked at the `${dataInflection(dataQuantity)}`