funcrithmetic

Monadic wrapper for doing arithmetic operations in JavaScript

• Goal
• Usage
• Guarding against non-numbers
• Advanced usage
• Development

Goal

The main goal of funcrithmetic is to facilitate writing conventional arithmetic equations in a more straightforward way:

const goldenSection = (Math.sqrt(5) + 1) / 2
// vs.
const goldenSection = FR.of(5)
  .sqr()
  .add(1)
  .div(2)
  .valueOf()
// => 1.618033988749895

The module aims to expose arithmetic operators in an easy-to-use fashion as well as acting as a Maybe Monad. If the term "Maybe Monad" throws you off, or the terms "Applicative" and "Functor" mean nothing to you, don't worry. You don't need to care all that much about these extra capabilities. The module can be used without ever touching this part of the API.

It is however worth noting that because funcrithmetic is a "Maybe Monad", it guards you against non-number values, including undefined and null (more on this later).

Usage

To use funcrithmetic, an "entry point" for the arithmetic equation is picked - in this case the 5 - and the subsequent operators are chained in the desired order. The more complicated the equation is, the more the simplicity of the chain notation becomes apparent:

const truncatedPentagon = Math.sqrt((5 - Math.sqrt(5)) / 2)
// vs.
const truncatedPentagon = FR.of(5)
  .sqrt()
  .subFrom(5)
  .div(2)
  .sqrt()
  .valueOf()
// => 1.1755705045849463

Notice the FR.of in the beginning of the expression? This is how values are "lifted" into the wrapper in order to get access to the arithmetic methods on it. Similarly the .valueOf() unwraps the value again:

const wrappedFive = FR.of(5)
// => FR(5)

const wrappedTwentyFive = wrappedFive.sqr()
// => FR(25)

const wrappedTwenty = wrappedTwentyFive.sub(5)
// => FR(20)

const twenty = wrappedTwenty.valueOf()
// => 20

That's basically it.

• .of(x): lifts a value into the wrapper.
• .valueOf(): unwraps the value again.

The exposed arithmetic methods on the wrapped value are:

• .add(x): adds x to the value.
• .dec(): decreases the value by 1.
• .div(x): divides the value by x.
• .inc(): increases the value by 1.
• .exp(x): exponentiates the value by x.
• .mul(x): multiplies the value by x.
• .neg(): negates the value.
• .sub(x): subtracts x from the value.
• .subFrom(x): subtracts the value from x.
• .sqr(): squares the value.
• .sqrt(): calculates the square root of the value.

Guarding against non-numbers

In order to be able to chain methods as long as you want without worrying about e.g. undefined or NaN, funcrithmetic guards against any non-number values internally:

FR.of('foo').add(2).valueOf()
// => undefined

FR.of(2).add('foo').valueOf()
// => undefined

FR.of(2).div(0).valueOf()
// => undefined

FR.of(-4).sqrt().valueOf()
// => undefined

Note that funcrithmetic regards Infinity and NaN as non-numbers. This is why FR.of(2).div(0).valueOf() doesn't yield Infinity and FR.of(-4).sqrt().valueOf() doesn't yield NaN.

Advanced usage

Because funcrithmetic is monadic, some extra methods are exist on the wrapper:

• .map(f): takes any function f and applies it to the value.
• .chain(f): takes any function f that returns a funcrithmetic wrapper and applies it to the value.
• .ap(fr): applies a wrapper to another wrapper that holds a function.

Using .map:

const res = FR.of(64).map(x => Math.sqrt(x) * 2 + 5).valueOf()
// => 21

Using .chain:

const res = FR.of(10).chain(x => FR.of(x * x)).valueOf()
// => 100

Using .ap:

const add = a => b => a + b

const res = FR.of(add)
  .ap(FR.of(3).sqr())
  .ap(FR.of(4).sqr())
  .sqrt()
  .valueOf()
// => 5

Note that the function has to be curried in order to apply the wrappers one by one.

Installation

The module is distributed via npm:

npm install funcrithmetic

And can be imported as a ES2015 module or CommonJS module depending on you setup:

import FR from 'funcrithmetic'

const FR = require('funcrithmetic')

Development

Run tests on watch mode:

npm run dev

Run tests and ensure proper code formatting:

npm test

Automatically format the source code including tests:

npm run prettier