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In a lot of daily tasks in programming we come across patterns where we deal with lists of values. In JavaScript we'd reach to arrays to collect them, and luckily there are plenty of methods built-in to modify such an array, such as map, filter and reduce.

Things become more complex when we're dealing with lists that are infinite. In such a case we may reach to iterables. We could expect an iterable that continuously outputs numbers, counting up infinitely, or rather until it reaches the maximum integer.

When we're dealing with asynchronous lists of values things also become more complex. We're often confronted with event streams, where events or even regular values come in over time.

In either case what we're dealing with are essentially immutable, asynchronous iterables.

Wonka is a library to provide a primitive to solve these problems and is both an iterable programming library and a reactive stream programming library.

It can be compared to observables and iterables in one library, but is based on and essentially a "callbag" library.

Sources, Operators, and Sinks

When we're thinking of solving problems with streams, it's always a good idea to look at how we're solving problems with arrays.

Since Wonka's streams are an entirely new primitive, Wonka has to provide all utilities that you as a developer may need to work with them. Specifically we have to make sure that it's easy to create, transform, and consume these streams.

If we compare these utilities to arrays, creating an array is similar to creating a stream. So Wonka has utilities such as fromArray to create a new source.

A source is what we call a stream in Wonka. This is because it doesn't strictly follow the definition or specification of observables nor iterables. So we're calling them sources since they're just a source of values over time.

Next we would like to transform sources to make them useful. Like with arrays we may want to map, filter, and reduce them, so Wonka has operators like filter and map. But since Wonka is like a toolkit, it comes with a lot more utilities than just that.

In general, operators will accept some arguments and a source and output a new, transformed source.

Lastly, the sources we create wouldn't be of much use if we weren't able to consume them. This is similar to using forEach on an array to iterate over its values. Wonka has a subscribe function which works similarly to how an observable's subscribe method may work. This is because Wonka's sources are entirely cancellable.

To summarise, Wonka's streams are sources of values, which can be transformed using operators, which create new sources. If we want to consume a source we use a sink.