by gcanti

gcanti / fp-ts

Functional programming in TypeScript

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Functional programming in TypeScript

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Typed functional programming in TypeScript

is a library for typed functional programming in TypeScript.

aims to allow developers to use popular patterns and abstractions that are available in most functional languages. For this, it includes the most popular data types, type classes and abstractions such as Option, Either, IO, Task, Functor, Applicative, Monad to empower users to write pure FP apps and libraries built atop higher order abstractions.

A distinctive feature of

with respect to other functional libraries is its implementation of Higher Kinded Types, which TypeScript doesn't support natively.

Inspired by

Table of contents


To install the stable version:

npm install fp-ts

Make sure to always have a single version of

installed in your project. Multiple versions are known to cause
to hang during compilation. You can check the versions currently installed using
npm ls fp-ts
(make sure there's a single version and all the others are marked as

TypeScript compatibility

Strictness – This library is conceived, tested and is supposed to be consumed by TypeScript with the

flag turned on.


version | required
version | | --------------- | ----------------------------- | | 2.0.x+ | 3.5+ | | 1.15.x+ | 3.1+ | | <= 1.14.4 | 2.8+ (*) |

(*) If you are running

< [email protected]
you have to polyfill the
type. You can use unknown-ts as a polyfill.


Disclaimer. Teaching functional programming is out of scope of this project, so the documentation assumes you already know what FP is.



The MIT License (MIT)

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