thomascothran / fp-ts

Functional programming in TypeScript

Functional programming in TypeScript

What is fp-ts?

fp-ts is a library for typed functional programming in TypeScript.

fp-ts 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 fp-ts with respect to other functional libraries is its implementation of Higher Kinded Types (TypeScript doesn't support HKT natively).

The idea (faking higher kinded types in TypeScript) is based on Lightweight higher-kinded polymorphism

Inspired by

• Haskell
• PureScript
• Scala

Table of Contents

• Installation and TypeScript compatibility
• Getting started
• Documentation
  • Blog posts
  • Tutorials
• Ecosystem
  • Libraries
  • Bindings
• Type Classes Diagram
• License

Installation and TypeScript compatibility

To install the stable version:

npm install fp-ts

The stable version is tested against TypeScript 3.3.3, but should run with TypeScript 2.8.0+ too

Note. This library is conceived, tested and is supposed to be consumed by TypeScript with the strict flag turned on.

Note. If you are running < typescript@3.0.1 you have to polyfill the unknown type. You can use unknown-ts as a polyfill.

Note. Make sure to always have a single version of fp-ts installed in your project. Multiple versions are known to cause tsc 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 deduped).

Getting started

If you are coming from JavaScript:

• read Mostly adequate guide to FP by @DrBoolean
• read this blog series on functional programming in JavaScript by Tom Harding, and then check out the code translated to TypeScript (there's a file for each blog post)

If you are using ramda

• Comparison with ramda

If you are coming from TypeScript:

• How to write type class instances for your data structures

If you are coming from Haskell or Purescript:

• Comparison with PureScript

Documentation

• API Reference

Blog posts

• Interoperability with non functional code using fp-ts
• Functional design: combinators
• Functional design: how to make the time combinator more general
• Functional design: tagless final

Tutorials

Beginner

• Debugging using the Trace module (code)

Advanced

• Free monad and fp-ts (code)
• MTL-style in fp-ts (code)
• Type safe finite state machines with IxIO (code)

Ecosystem

Libraries

• fp-ts-codegen - TypeScript code generation from a haskell-like syntax for ADT
• io-ts - TypeScript compatible runtime type system for IO validation
• monocle-ts - Functional optics: a (partial) porting of scala monocle to TypeScript
• newtype-ts - Implementation of newtypes in TypeScript
• logging-ts - Composable loggers for TypeScript
• fp-ts-routing - A type-safe bidirectional routing library for TypeScript
• parser-ts - String parser combinators for TypeScript
• remote-data-ts - RemoteData type (check this article)
• retry-ts - Retry combinators for monadic actions that may fail
• fp-ts-local-storage - fp-ts bindings for LocalStorage
• circuit-breaker-monad - Circuit Breaker pattern as a monad

Bindings

• fp-ts-rxjs - fp-ts bindings for RxJS
• fp-ts-fluture - fp-ts bindings for Fluture
• fp-ts-most - fp-ts bindings for @most/core

Type Classes Diagram

(click on the diagram to enlarge)

License

The MIT License (MIT)