A fast push & pull stream library for Reason, loosely following the callbag spec

“There’s no earthly way of knowing
Which direction we are going
There’s no knowing where we’re rowing
Or which way the river’s flowing” － Willy Wonka

• What is Wonka
• Why it exists
• Installation
• Getting Started
• Documentation (In Progress)

Wonka is a library for lightweight observables and iterables loosely based on the callbag spec. It exposes a set of helpers to create and transform sources and output sinks, meaning it helps you to turn an event source or an iterable set of data into streams, and manipulate these streams.

Reason has been becoming increasingly popular, but it's missing a good pattern for streams that feels native to the language. The functional nature of callbags make them a perfect starting point to fix this, and to introduce a reactive programming pattern to a language that is well suited for it.

Hence Wonka is a library that aims to make complex streams of data easy to deal with.

Install the library first: yarn add wonka or npm install --save wonka,

Then add wonka to bs-dependencies in your bsconfig.json file like so:

{
  "name": "<your name>",
  "version": "0.1.0",
  "sources": ["src"],
  "bsc-flags": ["-bs-super-errors"],
  "bs-dependencies": [
+    "wonka"
  ]
}

Writing your first stream is very easy! Let's suppose you would like to create a stream from a list, filter out some values, then map over the remaining ones, and lastly iterate over the final values.

This can be done with a few operators that might remind you of functions you would also call on iterables.

let example = [1, 2, 3, 4, 5, 6];

Wonka.fromList(example)
  |> Wonka.filter((.x) => x mod 2 === 0)
  |> Wonka.map((.x )=> x * 2)
  |> Wonka.forEach((.x) => print_endline(string_of_int(x)));

/* prints: 4, 8, 12 */

To explain what's going on:

• fromList creates a pullable source with values from the list
• filter only lets even values through
• map multiplies the values by 2
• forEach pulls values from the resulting source and prints them

As you can see, all helpers that we've used are exposed on the Wonka module. But if we would like to use JavaScript-based APIs, then we need to use the WonkaJs module.

Let's look at the same example, but instead of a list we will use an interval stream. This stream will output ascending numbers starting from 0 indefinitely.

We will code the same example as before but we'd like the interval to push a new number every 50ms and to stop after seven values.

WonkaJs.interval(50)
  |> Wonka.take(7)
  |> Wonka.filter((.x) => x mod 2 === 0)
  |> Wonka.map((.x) => x * 2)
  |> Wonka.forEach((.x) => print_endline(string_of_int(x)));

/* prints: 4, 8, 12 */

The last three functions stay the same, but we are now using interval as our source. This is a listenable source, meaning that it pushes values downwards when it sees fit. And the take operator tells our source to stop sending values after having received seven values.

And already you have mastered all the basics of Wonka and learned about a couple of its operators! Go, you! 🎉

I am currently still working on getting some documentation up and running. Those will contain:

• The API, i.e. a list of all helpers
• Examples
• Usage Guides & Recipes
• Developer Guides (How to write a source/operator/sink)
• Modified Callbag spec

Stay tuned and read the signature files in the meantime please:

• wonka.rei
• wonkaJs.rei