https://github.com/ericgj/adt.py

Tagged union types and immutable records (product types) in Python
https://github.com/ericgj/adt.py

Last synced: about 2 months ago
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Tagged union types and immutable records (product types) in Python

• Host: GitHub
• URL: https://github.com/ericgj/adt.py
• Owner: ericgj
• Created: 2017-01-26T03:16:09.000Z (almost 8 years ago)
• Default Branch: master
• Last Pushed: 2017-06-05T16:40:26.000Z (over 7 years ago)
• Last Synced: 2024-10-11T04:50:17.429Z (3 months ago)
• Language: Python
• Size: 7.81 KB
• Stars: 11
• Watchers: 2
• Forks: 2
• Open Issues: 0
• Metadata Files:
  • Readme: README.md

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README

        
# adt.py

Simple algebraic data types in Python

  - records (product types)

  - tagged unions (sum types)

  - simple tag-based pattern matching

  - immutable structures

  - records and tagged unions can be pickled/unpickled

  - python 2 and 3 compatible

Tip of the hat to [union-type](https://github.com/paldelpind/union-type), a

javascript library with similar aims and syntax.

## Tagged unions

    Point = Type("Point", [int, int])

    Rectangle = Type("Rectangle", [Point, Point])

    Circle = Type("Circle", [int, Point])

    

    # a union is defined as a sequence of types

    Shape = [ Rectangle, Circle ]

    

    # that then can be matched on

    area = match(Shape, {

      Rectangle: (lambda (t,l), (b,r): (b - t) * (r - l)),

      Circle: (lambda r, _: math.pi * (r**2))

    })

    

    rect = Rectangle( Point(0,0), Point(100,100) )

    area(rect)  # => 10000

    

    circ = Circle( 5, Point(0,0) )

    area(circ)  # => 78.539816...

Note that this is python 2 syntax. Python 3 sadly removed destructuring 

parameters in lambdas, so you have to do something like:

    area = match(Shape, {

      Rectangle: (lambda tl, br: (br[0] - tl[0]) * (br[1] - tl[1])),

      Circle: (lambda r, _: math.pi * (r**2))

    })

## Records

     Point = Record("Point", {'x': int, 'y': int})

     

     # types can be composed of records

     Rectangle = Type("Rectangle", [Point, Point])

     

     # and records composed of types

     Circle = Record("Circle", {'radius': int, 'center': Point} )

     Shape = [ Rectangle, Circle ]

     # including records composed of union types

     ScaledShape = Record("ScaledShape", {'shape': Shape, 'scale': int})

     

     p1 = Point(x=1,y=2)

     p2 = Point(x=4,y=6)

     rect = Rectangle( p1, p2 )

     srect = ScaledShape(shape=rect, scale=10) 

## To install

    pip install adt.py

## License

Copyright (c) 2017 Eric Gjertsen 

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.