Python `cons`

An implementation of cons in Python.

Usage and Design

The cons package attempts to emulate the semantics of Lisp/Scheme's cons as closely as possible while incorporating all the built-in Python sequence types:

>>> from cons import cons, car, cdr
>>> cons(1, [])
[1]

>>> cons(1, ())
(1,)

>>> cons(1, [2, 3])
[1, 2, 3]

In general, cons is designed to work with collections.abc.Sequence types.

According to the cons package, None corresponds to the empty built-in list, as nil does in some Lisps:

>>> cons(1, None)
[1]

The cons package follows Scheme-like semantics for empty sequences:

>>> car([])
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ConsError: Not a cons pair

>>> cdr([])
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ConsError: Not a cons pair

By default, str types are not considered cons-pairs, although they are sequences:

>>> cons("a", "string")
ConsPair('a' 'a string')

This setting can be overridden and other types can be similarly excluded from consideration by registering classes with the abc-based classes MaybeCons and NonCons.

Features

Built-in support for the standard Python ordered sequence types: i.e. list, tuple, Iterator, OrderedDict.

>>> from collections import OrderedDict
>>> cons(('a', 1), OrderedDict())
OrderedDict([('a', 1)])

Existing cons behavior can be changed and support for new collections can be added through the generic functions cons.core._car and cons.core._cdr.
Built-in support for unification.

>>> from unification import unify, reify, var
>>> unify([1, 2], cons(var('car'), var('cdr')), {})
{~car: 1, ~cdr: [2]}

>>> reify(cons(1, var('cdr')), {var('cdr'): [2, 3]})
[1, 2, 3]

>>> reify(cons(1, var('cdr')), {var('cdr'): None})
[1]

Installation

pip install cons

Release files for cons 0.3.0

For a detailed explanation of source distributions (sdists) and built distributions (wheels), please see the package formats documentation.

Source distribution (sdist)

Source distribution for cons 0.3.0
File	Size	Uploaded
cons-0.3.0.tar.gz	21.3 kB	Feb 1, 2020	Details

Built distribution (wheel)

Table of built distributions (wheels) for cons 0.3.0
File	Interpreter	ABI	Platform	Reset
cons-0.3.0-py3-none-any.whl 6.0 kB Feb 1, 2020	Python 3	none	any	Details

Total release size: 27.4 kB

Release files / cons-0.3.0.tar.gz

Download URL	cons-0.3.0.tar.gz
Size	21.3 kB
Tags	Source
SHA-256 checksum How to use checksums	`6a8e9bb4ed715fe701b8a03b2b93d3f8dfff4bd38944bf47b0a2230ef98efb1a`
BLAKE2b-256 checksum How to use checksums	`98a79971261a064bf47239c396477b4fe39ad4f6c622ff9b81fff7807f88b059`
Upload date	Feb 1, 2020
Uploaded using Trusted Publishing? What is trusted publishing?	No
Uploaded via	`twine/1.15.0 pkginfo/1.5.0.1 requests/2.22.0 setuptools/41.0.1 requests-toolbelt/0.9.1 tqdm/4.36.1 CPython/3.7.3`

Release files / cons-0.3.0-py3-none-any.whl

Download URL	cons-0.3.0-py3-none-any.whl
Size	6.0 kB
Tags	Python 3
SHA-256 checksum How to use checksums	`bd08cb4d7e2f6589238abcee7282a6b03d0686adfacc875b59242deb9e528ad7`
BLAKE2b-256 checksum How to use checksums	`73a5d402c4d155e9ae0400f96d84203c2057e8b8456f8358668850083b207786`
Upload date	Feb 1, 2020
Uploaded using Trusted Publishing? What is trusted publishing?	No
Uploaded via	`twine/1.15.0 pkginfo/1.5.0.1 requests/2.22.0 setuptools/41.0.1 requests-toolbelt/0.9.1 tqdm/4.36.1 CPython/3.7.3`