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Data structures and utilities for monadic style functional programming.

Project description

PyMonad implements data structures typically available in pure functional or functional first programming languages like Haskell and F#. Included are Monad and Monoid data types with several common monads included - such as Maybe and State - as well as some useful tools such as the @curry decorator for defining curried functions. PyMonad 2.0.x represents and almost complete re-write of the library with a simpler, more consistent interface as well as type annotations to help ensure correct usage.

1 Getting Started

These instructions will get you a copy of the project up and running on your local machine for development and testing purposes.

1.1 Prerequisites

PyMonad requires Python 3.7+. If installing via pip then you will also need Pip and Wheel installed. See those projects for more information on installing them if necessary.

Potential contributors should additionally install pylint and pytype to ensure their code adheres to common style conventions.

1.2 Installing

1.2.1 From the Python Package Index (PyPI) with pip

From a command line run:

pip install PyMonad

1.2.2 Manual Build from PyPI

Download the project files from and from the project directory run:

python install

If that doesn’t work you may need to run the following instead.

python3 install

1.2.3 From github

Clone the project repository:

git clone

Then from the project directory run as for the manual build instructions above.

1.2.4 Example Usage

The following example imports the tools module and uses the curry function to define a curried addition function.

import # Pass the expected number of arguments to the curry function.
def add(x, y):
    return x + y

# We can call add with all of it's arguments...
print(add(2, 3)) # Prints '5'

# ...or only some of them.
add2 = add(2)  # Creates a new function expecting a single arguments
print(add2(3)) # Also prints '5'

1.2.5 Next Steps

The PyMonad documentation is a work in progress. For tutorials, how-to, and more head over to the PyMonad Documentation Project. If you’d like to contribute visit the documentation repository here.

2 Running the tests

2.1 Unit Tests

These tests primarily ensure that the defined monads and monoids obey the required mathematical laws.

On most *nix systems you should be able to run the automated tests by typing the following at the command line.


However, is just a convenience. If the above doesn’t work the following should:

python3 -m unittest discover test/

2.2 Style Tests

Contributors only need to run pylint and pytype over their code and ensure that there are no glaring style or type errors. PyMonad (mostly) attempts to adhere to the Google Python Style Guide and includes type hinting according to PEP 484.

In general, don’t disable pylint or pytype errors for the whole project, instead disable them via comments in the code. See the existing code for examples of errors which can be disabled.

3 Authors

Jason DeLaat - Primary Author/Maintainer -

4 License

This project is licensed under the 3-Clause BSD License. See LICENSE.rst for details.

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