Package `clingo`

Module providing functions and classes to control the grounding and solving process.

Next follow some concepts used throughout the modules of the clingo package.

Terms

Terms without variables and interpreted functions are called symbols in the following. They are wrapped in the Symbol class.

Symbolic Atoms And Literals

Symbolic atoms without variables and interpreted functions, which appear in ground logic programs, are captured using the Symbol class. They must be of type SymbolType.Function. Furthermore, some functions accept symbolic literals, which are represented as pairs of symbols and Booleans. The Boolean stands for the sign of the literal (True for positive and False for negative).

Program Literals

When passing a ground logic program to a solver, clingo does not use a human readable textual representation but the aspif format. The literals in this format are called program literals. They are non-zero integers associated with symbolic atoms, theory atoms, and also without any association if they are used to translate complex language constructs not directly representable in aspif format. The sign of a program literal is used to represent default negation. Symbolic atoms can be mapped to program literals using the clingo.symbolic_atoms module and theory atoms using the clingo.theory_atoms module. Note that symbolic and theory atoms can share the same program literals. Finally, the clingo.backend module can also be used to introduce fresh symbolic atoms and program literals.

Solver Literals

Before solving, programs in aspif format are translated to an internal solver representation, where program literals are again mapped to non-zero integers, so called solver literals. The PropagateInit.solver_literal() function can be used to map program literals to solver literals. Note that different program literals can share the same solver literal.

Embedded Python Code

If the clingo application is build with Python support, clingo will also be able to execute Python code embedded in logic programs. Functions defined in a Python script block are callable during the instantiation process using @-syntax. The default grounding/solving process can be customized if a main function is provided.

Examples

The first example shows how to use the clingo module from Python.

>>> from clingo.symbol import Number
>>> from clingo.control import Control
>>>
>>> class Context:
...     def inc(self, x):
...         return Number(x.number + 1)
...     def seq(self, x, y):
...         return [x, y]
...
>>> def on_model(m):
...     print (m)
...
>>> ctl = Control()
>>> ctl.add("base", [], """\
... p(@inc(10)).
... q(@seq(1,2)).
... """)
>>> ctl.ground([("base", [])], context=Context())
>>> print(ctl.solve(on_model=on_model))
p(11) q(1) q(2)
SAT

The second example shows how to use Python code from clingo.

#script (python)

from clingo.symbol import Number

class Context:
    def inc(self, x):
        return Number(x.number + 1)

    def seq(self, x, y):
        return [x, y]

def main(prg):
    prg.ground([("base", [])], context=Context())
    prg.solve()

#end.

p(@inc(10)).
q(@seq(1,2)).

Sub-modules

clingo.application: Functions and classes to implement applications based on clingo …
clingo.ast: Module to work with clingo's non-ground program representation …
clingo.backend: Functions and classes to observe or add ground statements …
clingo.configuration: Functions and classes related to configuration …
clingo.control: This module contains the Control class responsible for controling grounding and solving …
clingo.core: Core functionality used throught the clingo package.
clingo.propagator: Functions and classes to implement custom propagators …
clingo.script: This module contains functions to add custom scripts, which can be embedded into logic programs …
clingo.solving: Functions and classes related to solving …
clingo.statistics: Functions and classes related to statistics …
clingo.symbol: Functions and classes for symbol manipulation …
clingo.symbolic_atoms: Functions and classes to work with symbolic atoms …
clingo.tests: Unit tests for the clingo package.
clingo.theory: This module defines the Theory class for using a [CFFI] based module with clingo's Python package …
clingo.theory_atoms: Functions and classes to work with theory atoms …
clingo.util: Utility functions and classes.