Logical Unification

Logical unification in Python, extensible via dispatch.

Installation

Using pip:

pip install logical-unification

To install from source:

git clone git@github.com:pythological/unification.git
cd unification
pip install -r requirements.txt

Tests can be run with the provided Makefile:

make check

Examples

unification has built-in support for most Python data types:

>>> from unification import *
>>> unify(1, 1)
{}
>>> unify(1, 2)
False
>>> x = var('x')
>>> unify((1, x), (1, 2))
{~x: 2}
>>> unify((x, x), (1, 2))
False

Custom classes can be made "unifiable" with the unifiable decorator:

@unifiable
class Account(object):
    def __init__(self, id, name, balance):
        self.id = id
        self.name = name
        self.balance = balance

>>> data = [Account(1, 'Alice', 100),
            Account(2, 'Bob', 0),
            Account(2, 'Charlie', 0),
            Account(2, 'Denis', 400),
            Account(2, 'Edith', 500)]
>>> id, name, balance = var('id'), var('name'), var('balance')
>>> [unify(Account(id, name, balance), acct) for acct in data]
[{~name: 'Alice', ~balance: 100, ~id: 1},
{~name: 'Bob', ~balance: 0, ~id: 2},
{~name: 'Charlie', ~balance: 0, ~id: 2},
{~name: 'Denis', ~balance: 400, ~id: 2},
{~name: 'Edith', ~balance: 500, ~id: 2}]
>>> [unify(Account(id, name, 0), acct) for acct in data]
[False,
{~name: 'Bob', ~id: 2},
{~name: 'Charlie', ~id: 2},
False,
False]

unification also supports function dispatch through pattern matching:

>> from unification.match import *
>>> n = var('n')

@match(0)
def fib(n):
    return 0


@match(1)
def fib(n):
    return 1


@match(n)
def fib(n):
    return fib(n - 1) + fib(n - 2)

>>> map(fib, [0, 1, 2, 3, 4, 5, 6, 7, 8, 0])
[0, 1, 1, 2, 3, 5, 8, 13, 21, 34]

The pattern matching can be fairly complex:

>> name, amount = var('name'), var('amount')

@match({'status': 200, 'data': {'name': name, 'credit': amount}})
def respond(name, amount):
    balance[name] +=  amount


@match({'status': 200, 'data': {'name': name, 'debit': amount}})
def respond(name, amount):
    balance[name] -= amount


@match({'status': 404})
def respond():
    print("Bad Request")

See the full example in the examples directory.

Performance and Reliability

unification's current design allows for unification and reification of nested structures that break the Python stack recursion limit. This scalability incurs an overhead cost compared to simple stack-based recursive unification/reificiation.

About

This project is a fork of unification.