An implementation of Lisp/Scheme-like cons in Python.
Project description
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]
>>> cons(1, "a string")
ConsPair(1 'a string')
According to cons
, None
corresponds to the empty built-in list
:
>>> 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
Features
- Support for the standard Python ordered collection types: i.e.
list
,tuple
,Iterator
,OrderedDict
.
>>> from collections import OrderedDict
>>> cons(('a', 1), OrderedDict())
OrderedDict([('a', 1)])
- Existing
cons
behavior is easy to change and new collections are straightforward to add throughmultipledispatch
. - 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
Project details
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