fp-booleans

A collection of utility functions to apply boolean logic on functions (including higher-order):

1. not()
2. and()
3. or()

Written (and can be used) in a functional programming style.

fp-booleans functions are:

1. pure
2. tiny
3. zero-dependencies
4. tree-shakeable
5. 100% tested by design

Why

Being able to combine or negate booleans, boolean predicate functions and higher-order functions means lots of 💪 power. With a flexible yet simple API and TS annotations this can be easy too.

Examples

not()

On boolean values (or expressions)

Imagine we want to pass or fail a level in a game based on the score being greater than 100:

const greaterThan100 = (n: number) => n > 100;
const pass = greaterThan100(score);
const fail = !pass;

The ! only works on the boolean value (or equivalent expression), not on the function reference.

In this case we could use not() to just reverse the boolean value or expression. (nothing fancy here, just equivalent to !)

const fail = not(pass);

but not() proves already useful as it can be used as mapper:

const flippedValues = [true, false].map(not); // [false, true]

Now on the 🥭 juicy parts:

On boolean predicates

We can use not() on a function (boolean predicate) to "reverse" it and get a function with the same signature but opposite logic

const notGreaterThan100 = not(greaterThan100);
const fail = notGreaterThan100(score);
// same as
const fail = not(greaterThan100)(score)

On a higher order functions

The best part is we can also use it on a higher-order function that returns a boolean predicate:

const greaterThan = (comparison: number) => (arg: number) => arg > comparison;

// we now have several options:

// we could just reverse the boolean value
const fail = not(greaterThan(100)(score))
// or the partially-applied HoF (boolean predicate)
const fail = not(greaterThan(100))(score);
// or reverse the higher-order function itself
const fail = not(greaterThan)(100)(score);

[!TIP] Being able to move parenthesis around is not for the sake of 🤹 juggling code. This flexibility allows to have the complexity (and unit tests) in one single function, partially apply it as much as needed and then applying boolean operations on the specialized function without the need of writing several similar functions (and testing them).Imagine if instead than a simple score > 100 logic in our examples we had a complex function… Negating it or combining it could require writing several slightly different versions of the logic (that should all be unit tested). With not() we can avoid code duplication.

and()

Combining functions is a foundation of functional programming.

Imagine again some code where we are granting a special bonus score based on some logic:

const isBonusScore = score => score % 2 === 0 && score > 0 && score <= 100;

This code, while still being simple, is hard to read, to test and maintain. This kind of code tends to be infused with business logic and be rewritten with mild differences in several places. Combining simpler functions would help almost not writing code and ease readability using a declarative syntax.

The first step would be to isolate simpler abstract functions:

const isEven = n => n % 2 === 0;
const isGreaterThan = compare => n => n > compare;
const isBetween = (min, max) => isGreaterThan(min) && not(isGreaterThan(max));

[!NOTE] This is a one-time job (or no job at all if you already have them or use some external package) and once tested these functions are going to be bullet-proof.

With these utils in place, we could create one function that combines expressions (booleans) with the && operator, but it would require to have a function signature, invoke all functions, and passing the same parameter and would look like:

const isBonusScore = score => isEven(score) && isBetween(0, 100)(score);

Instead, we could just and() (combine the function references) and go point-free.

const isBonusScore = and(isEven, isBetween(0, 100));
console.log(isBonusScore(50)); // true

See how combining functions references is more compact than combining expressions in a function?

or()

All we just said about the and() function applies here. E.g.:

const isValid = or(isNegative, isGreaterThan(100));

All together

fp-booleans functions can be all combined to unleash infinite 🚀 power:

not(is(5));
and(gte(MIN_PRICE), not(isRound));
or(is('admin'), and(startsWith('user_'), isLowerCase));

Used in filters

Can be used in filters:

array.filter(not(is(5)));
array.filter(and(gte(MIN_PRICE), not(isRound)));
array.filter(or(is('admin'), and(startsWith('user_'), isLowerCase)));

[!TIP] fp-booleans is a core part of fp-filters, a curated list of filter functions

Getting started

Installation

fp-booleans runs on Node.js and is available as a NPM package.

npm install --save fp-booleans

or

yarn add fp-booleans

Contributions

Looking forward for some help.

MIT

Copyright (c) 2023-present, Pierluigi Pesenti (Oaxoa)