Prelude-IO

This library aims to provide easy to use run- and compiletime type-safety combined with the benefits of immutability through Prelude-ts.

Interop with Prelude-ts is a key feature of this library, but not strictly required for operation.

Core library

Prelude-IO's base unit is the Bus<I, O> class, which provides basic functionality and abstractions around creating reversible data pipelines. The core library also includes a few basic types to represent most data formats, found here under Presets.

Examples can be found here. Alternatively, here's an overview of some basic functionality:

import * as io from "prelude-io";
import { Predicate } from "prelude-ts";

// Conditional types
const rating = io.number.if(Predicate.of((n) => n > 0 && n <= 5));

// Complex types
const roomType = io.Complex("Room", {
  name: io.string.
  description: io.Optional(io.string),
  rating: rating,
});

// Nesting
const hotelType = io.Complex("Hotel", {
  address: io.string,
  website: io.string,
  rating: rating
  rooms: io.Vector(Room)
});

// Deserialising
fetch("http://example.com/hotels.json")
  .then(response => response.json())
  // (de)serialising
  .then(HotelType.deserialise)
  .then(hotel => {
    // Either-based error handling
    if(hotel.isLeft()) {
      // Built-in debugger
      console.error(io.humanizeErrors(hotel.getLeft()))
    } else {
      LocalStorage.setItem("hotel", hotel.get())
    }
  });

Documentation

You can read typedoc documentation here

Installation

npm install --save @prelude-io/core prelude-ts

Principles

• Busses split parsing and conditional logic into seperate functions
• IO returns Either objects rather than throw exceptions
• Functions can be chained or turned into a union

Additional libraries

• Prelude-IO/Fetch: A wrapper around fetch for runtime type-checking

Roadmap

• Add extra commonly used types
• @prelude-io/test: A set of functions to run basic tests on your data types

Inspirations

• Prelude-ts: Provides functional programming concepts in an accessible manner. Though a similar name, this project is not directly affiliated with prelude-ts or its authors.
• io-ts: Runtime type checking, encoding and decoding, based on fp-ts.