# dry-monads
[](https://wemake.services) [](https://travis-ci.org/sobolevn/dry-monads) [](https://coveralls.io/github/sobolevn/dry-monads?branch=master) [](https://dry-monads.readthedocs.io/en/latest/?badge=latest) [](https://pypi.org/project/dry-monads/) [](https://github.com/wemake-services/wemake-python-styleguide)
Monads for `python` made simple and safe.
## Features
- Provides primitives to write declarative business logic
- Fully typed with annotations and checked with `mypy`,
allowing you to write type-safe code as well
- No operator overloading or other unpythonic stuff that makes your eyes bleed
## Installation
```bash
pip install dry-monads
```
## What's inside?
We have several the most iconic monads inside:
- [Result, Failure, and Success](https://dry-monads.readthedocs.io/en/latest/pages/either.html) (also known as `Either`, `Left`, and `Right`)
- [Maybe, Some, and Nothing](https://dry-monads.readthedocs.io/en/latest/pages/maybe.html)
We also care about code readability and developer experience,
so we have included some useful features to make your life easier:
- [Do notation](https://dry-monads.readthedocs.io/en/latest/pages/do-notation.html)
- [Helper functions](https://dry-monads.readthedocs.io/en/latest/pages/functions.html)
## Example
```python
from dry_monads.do_notation import do_notation
from dry_monads.either import Result, Success, Failure
class CreateAccountAndUser(object):
"""Creates new Account-User pair."""
@do_notation
def __call__(self, username: str, email: str) -> Result['User', str]:
"""Can return a Success(user) or Failure(str_reason)."""
user_schema = self._validate_user(username, email).unwrap()
account = self._create_account(user_schema).unwrap()
return self._create_user(account)
# Protected methods
# ...
```
We are [covering what's going on in this example](https://dry-monads.readthedocs.io/en/latest/pages/do-notation.html) in the docs.
## Inspirations
This module is heavily based on:
- [dry-rb/dry-monads](https://github.com/dry-rb/dry-monads)
- [Ø](https://github.com/dbrattli/OSlash)
- [pymonad](https://bitbucket.org/jason_delaat/pymonad)
