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A simple python library for generating prolog terms

Project description

prologterms - a python library for constructing prolog terms

Example:

from prologterms import TermGenerator, PrologRenderer, Var

X = Var('X')
P = TermGenerator()
term = P.member(X, [1, 2, 3])
r = PrologRenderer()
print(r.render(term))

writes:

member(X, [1, 2, 3])

All prolog escaping conventions are handled automatically.

See the Jupyter notebook

Rules

The “<=” operator in python is overloaded to mean the same as prolog “:-”. This means a rule object can be created as follows:

P.ancestor(X,Y) <= (P.parent(X,Z), P.ancestor(Z,Y))

This can be done more explicitly using a Rule constructor:

from prologterms import TermGenerator, PrologRenderer, Var, Rule

X = Var('X')
Y = Var('Y')
Z = Var('Z')
P = TermGenerator()
rule = Rule(P.ancestor(X,Y), (P.parent(X,Z), P.ancestor(Z,Y))

Usage

This module is of little use by itself. It is intended to be used to generate prolog programs that can be fed into a prolog execution engine.

  • write prolog programs and queries to a file, and load these using an engine like swi-prolog
  • through web services, e.g. via pengines

Pengines

[Note: requires latest pengines which may not be on pypi]

One of the intended applications is pengines

from pengines.Builder import PengineBuilder
from pengines.Pengine import Pengine
from prologterms import TermGenerator, PrologRenderer, Program, Var

P = TermGenerator()
X = Var('X')
Y = Var('Y')
Z = Var('Z')
R = PrologRenderer()

p = Program(
    P.ancestor(X,Y) <= (P.parent(X,Z), P.ancestor(Z,Y)),
    P.ancestor(X,Y) <= P.parent(X,Y),
    P.parent('a','b'),
    P.parent('b','c'),
    P.parent('c','d')
)

q = P.ancestor(X,Y)

factory = PengineBuilder(urlserver="http://localhost:4242",
                         srctext=R.render(p),
                         ask=R.render(q))
pengine = Pengine(builder=factory, debug=True)
while pengine.currentQuery.hasMore:
    pengine.doNext(pengine.currentQuery)
for p in pengine.currentQuery.availProofs:
    print('{} <- {}'.format(p[X.name], p[Y.name]))

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