https://github.com/purescript/purescript-exists

Existential types as a library
https://github.com/purescript/purescript-exists

Last synced: 3 months ago
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Existential types as a library

• Host: GitHub
• URL: https://github.com/purescript/purescript-exists
• Owner: purescript
• License: bsd-3-clause
• Created: 2014-05-13T01:01:16.000Z (over 10 years ago)
• Default Branch: master
• Last Pushed: 2022-11-16T15:42:55.000Z (almost 2 years ago)
• Last Synced: 2024-04-23T09:49:26.680Z (7 months ago)
• Language: PureScript
• Homepage:
• Size: 37.1 KB
• Stars: 33
• Watchers: 4
• Forks: 9
• Open Issues: 4
• Metadata Files:
  • Readme: README.md
  • Changelog: CHANGELOG.md
  • License: LICENSE

Awesome Lists containing this project

• awesome-purescript - exists - Encodes existential types. (Essential libraries)

README

        
# purescript-exists

[![Latest release](http://img.shields.io/github/release/purescript/purescript-exists.svg)](https://github.com/purescript/purescript-exists/releases)

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[![Pursuit](https://pursuit.purescript.org/packages/purescript-exists/badge)](https://pursuit.purescript.org/packages/purescript-exists)

The `Exists` type, for encoding existential types.

## Installation

```

spago install exists

```

## Overview

The type `Exists f` is isomorphic to the existential type `exists a. f a`.

For example, consider the type `exists s. Tuple s (s -> Tuple s a)` which represents infinite streams of elements of type `a`.

This type can be constructed by creating a type constructor `StreamF` as follows:

```purescript

data StreamF a s = StreamF s (s -> Tuple s a)

```

We can then define the type of streams using `Exists`:

```purescript

type Stream a = Exists (StreamF a)

```

The `mkExists` and `runExists` functions then enable packing and unpacking of `SteamF` into/out of `Stream`.

## Documentation

Module documentation is [published on Pursuit](http://pursuit.purescript.org/packages/purescript-exists).