pyeither 0.0.2

An implementation of Data.Either from Haskell in Python

# 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)
.chain()
.bind(either.predicate(os.path.isfile, "not a file"))
.bind(lambda p: either.attempt(json.load, p))
.unchain())

# 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
```

## 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.