lazy-thunk/README.md

A set of data structures in TypeScript which utilizes lazy evaluation

# lazy-thunk

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> A set of data structures in TypeScript which utilizes lazy evaluation (w/o 3rd party dependencies!)

`lazy-thunk` emulates lazy evaluation simply by wrapping expressions into a function.

## Simple Examples

```ts
import { type Thunk, toThunk } from "lazy-thunk";
import * as LL from "lazy-thunk/LinkedList";

// an infinite list of even numbers
const isEven = (n: Thunk<number>) => n() % 2 === 0;
const evens = LL.filter(isEven, LL.range(1));
const xs = LL.unsafeToArray(LL.take(5, evens)); // [2, 4, 6, 8, 10]

// an infinite list of prime numbers
const sieve = (xs: LL.LazyList<Thunk<number>>): LL.LazyList<Thunk<number>> => {
  return () => {
    const node = xs();
    if (node === null) {
      return null;
    }
    const h = node.head;
    return {
      head: h,
      rest: sieve(LL.filter((n) => n() % h() !== 0, node.rest)),
    };
  };
};
const primes = sieve(LL.range(2));
const ys = LL.unsafeToArray(LL.take(5, primes)); // [2, 3, 5, 7, 11]
```

## Installation

```console
npm i lazy-thunk
```

## API

TODO

## About Naming

### Package

A [`thunk`](https://wiki.haskell.org/Thunk) is a term used in Haskell, which denotes value that is yet to be evaluated.

> [!IMPORTANT]
> lazy-thunk does not strictly emulates `thunk` in Haskell. Haskell evaluates expressions up to [WHNF (Weak Head Normal Form)](https://wiki.haskell.org/Weak_head_normal_form).

## References

- HaskellWiki: https://wiki.haskell.org/
- Basic idea comes from: https://youtu.be/E5yAoMaVCp0?si=slYqwH_GDHVTm-Ty

## License

This project is licensed under the terms of the [MIT License](LICENSE).