Metadata-Version: 2.1
Name: sumtypes
Version: 0.1a5
Summary: Algebraic types for Python (notably providing Sum Types, aka Tagged Unions)
Home-page: http://github.com/radix/sumtypes/
Author: Christopher Armstrong
Author-email: UNKNOWN
License: MIT
Platform: UNKNOWN
Classifier: License :: OSI Approved :: MIT License
Classifier: Programming Language :: Python :: 2
Classifier: Programming Language :: Python :: 3
Requires-Dist: attrs

sumtypes
========

.. image:: https://travis-ci.org/radix/sumtypes.svg?branch=master
    :target: https://travis-ci.org/radix/sumtypes

sumtypes provides Algebraic Data Types for Python. The main benefit is the
implementation of Sum Types (aka `Tagged Unions`_), which Python doesn't have
any native representation for. Product Types are just objects with multiple
attributes.

.. _`Tagged Unions`: http://en.wikipedia.org/wiki/Tagged_union

Documentation is at https://sumtypes.readthedocs.org/

This module uses the `attrs`_ library to provide features like attribute
validation and defaults.

.. _`attrs`: http://pypi.python.org/pypi/attrs

Example
=======

Decorate your classes to make them a sum type:

.. code:: python

    import attr
    from sumtypes import sumtype, constructor, match

    @sumtype
    class MyType(object):
        # constructors specify names for their arguments
        MyConstructor = constructor('x')
        AnotherConstructor = constructor('x', 'y')

        # You can also make use of any feature of the attrs
        # package by using attr.ib in constructors
        ThirdConstructor = constructor(
            one=attr.ib(default=42),
            two=attr.ib(validator=attr.validators.instance_of(int)))

(`attrs package`_, and `attr.ib documentation`_)

.. _`attrs package`: https://pypi.python.org/pypi/attrs
.. _`attr.ib documentation`: http://attrs.readthedocs.org/en/stable/api.html#attr.ib

Then construct them by calling the constructors:

.. code:: python

    v = MyType.MyConstructor(1)
    v2 = MyType.AnotherConstructor('foo', 2)

You can get the values from the tagged objects:

.. code:: python

    assert v.x == 1
    assert v2.x == 'foo'
    assert v2.y == 2

You check the constructor used:

.. code:: python

    assert type(v) is MyType.MyConstructor

And, like Scala case classes, the constructor type is a subclass of the main
type:

.. code:: python

    assert isinstance(v, MyType)

And the tagged objects support equality:

.. code:: python

    assert v == MyType.MyConstructor(1)
    assert v != MyType.MyConstructor(2)

Simple pattern matching is also supported. To write a function over all the
cases of a sum type:

.. code:: python

    @match(MyType)
    class get_number(object):
        def MyConstructor(x): return x
        def AnotherConstructor(x, y): return y
        def ThirdConstructor(one, two): return one + two

    assert get_number(v) == 1
    assert get_number(v2) == 2

``match`` ensures that all cases are handled. If you really want to write a
'partial function' (i.e. one that doesn't cover all cases), use
``match_partial``.


See Also
========

Over the past few years, the ecosystem of libraries to help with functional
programming in Python has exploded. Here are some libraries I recommend:

- `effect`_ - a library for isolating side-effects
- `pyrsistent`_ - persistent (optimized immutable) data structures in Python
- `toolz`_ - a general library of pure FP functions
- `fn.py`_ - a Scala-inspired set of tools, including a weird lambda syntax, option type, and monads

.. _`effect`: https://pypi.python.org/pypi/effect/
.. _`pyrsistent`: https://pypi.python.org/pypi/pyrsistent/
.. _`toolz`: https://pypi.python.org/pypi/toolz
.. _`fn.py`: https://pypi.python.org/pypi/fn


Thanks
======

Thanks to Rackspace for allowing me to work on this project, and having an
*excellent* `open source employee contribution policy`_

.. _`open source employee contribution policy`: https://www.rackspace.com/blog/rackspaces-policy-on-contributing-to-open-source/


License
=======

sumtypes is licensed under the MIT license:

Copyright (C) 2015 Christopher Armstrong

Permission is hereby granted, free of charge, to any person obtaining a copy of
this software and associated documentation files (the "Software"), to deal in
the Software without restriction, including without limitation the rights to
use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
the Software, and to permit persons to whom the Software is furnished to do so,
subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.


