https://github.com/segfaultax/pyeither

An implementation of Data.Either from Haskell in Python
https://github.com/segfaultax/pyeither

applicative either functional-programming functional-python functor haskell monad python

Last synced: 25 days ago
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An implementation of Data.Either from Haskell in Python

• Host: GitHub
• URL: https://github.com/segfaultax/pyeither
• Owner: SegFaultAX
• License: mit
• Created: 2018-01-12T01:50:54.000Z (almost 7 years ago)
• Default Branch: master
• Last Pushed: 2018-01-30T21:54:42.000Z (almost 7 years ago)
• Last Synced: 2024-09-13T04:31:18.465Z (about 2 months ago)
• Topics: applicative, either, functional-programming, functional-python, functor, haskell, monad, python
• Language: Jupyter Notebook
• Size: 33.2 KB
• Stars: 3
• Watchers: 2
• Forks: 1
• Open Issues: 0
• Metadata Files:
  • Readme: README.md
  • License: LICENSE.txt

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README

        
# pyeither

A functional Python library that exposes `Data.Either` from Haskell.

```haskell

data Either e a = Left e | Right a

```

## Example Usage

```python

import os

import json

import either

def main():

    path = "~/myfile.json"

    

    # Lift a normal value into Either

    e_path = either.pure(path)

    # Ensure the path is valid, returning Right(path) if it is or Left("not a file") if it isn't

    e_valid = e_path.bind(either.predicate(os.path.isfile, "not a file"))

    # Load a file as json, returning Right(contents) if it works, or Left(exc) if it doesn't

    e_data = e_valid.bind(lambda p: either.attempt(json.load, p))

    # It's annoying to assign intermediate values to variables, so you can chain expressions

    # Equivalent to above:

    e_data2 = (either.pure(path)

        .bind(either.predicate(os.path.isfile, "not a file"))

        .bind(lambda p: either.attempt(json.load, p)))

    # Python lacks do-notation, so there's not a nice equivalent syntax

    # Build pipelines of actions using monadic composition

    ensure_path = either.predicate(os.path.isfile, "not a file")

    load_file = lambda p: either.attempt(json.load, p)

    process = either.kleisli(ensure_path, load_file)

    # Equivalent to above:

    e_data3 = either.pure(path).bind(process)

```

## Getting pyeither

```

pip install pyeither

```

## Motivation

I've created an IPython Notebook that describes the motivation for this project

as an interactive tutorial building an analogous system from scratch. If you're

interested in learning more about the **why** of this project, please check it

out!

[**Motivation Notebook**](https://github.com/SegFaultAX/pyeither/blob/master/pyeither_demo.ipynb)

## Special Thanks

This library depends on the absolutely wonderful

[`attrs`](http://www.attrs.org/en/stable/) library, without which there would

have been far more ugly boilerplate.

## License

Copyright 2018 Michael-Keith Bernard 

See LICENSE.txt for the full license.