public void PicksCorrectVariablesInSimpleCase()
{
// Predicate p(X,Y) :- q(X, Z), r(Z,Y) should have Z and Y as permanent variables
var p = Literal.NewAtom();
var q = Literal.NewAtom();
var r = Literal.NewAtom();
var X = Literal.NewVariable();
var Y = Literal.NewVariable();
var Z = Literal.NewVariable();
var pXY = Literal.NewFunctor(2).With(X, Y);
var qXZ = Literal.NewFunctor(2).With(X, Z);
var rZY = Literal.NewFunctor(2).With(Z, Y);
// Create the clause
var clause = Clause.If(qXZ, rZY).Then(pXY);
// Compile to assignments
var allPredicates = new[] { clause.Implies }.Concat(clause.If).ToArray();
var assignmentList = allPredicates.Select(predicate => PredicateAssignmentList.FromPredicate(predicate));
// Get the set of permanent variables
var permanent = PermanentVariableAssignments.PermanentVariables(assignmentList);
// Z and Y are the only permanent variables
Assert.IsFalse(permanent.Contains(X));
Assert.IsTrue(permanent.Contains(Y));
Assert.IsTrue(permanent.Contains(Z));
Assert.AreEqual(2, permanent.Count);
}
/// <summary>
/// Queries a solver for a goal
/// </summary>
public static IQueryResult Query(this ISolver solver, ILiteral goal)
{
// Result is false for something without a key
if (goal.UnificationKey == null)
{
return(new BasicQueryResult(false, new EmptyBinding(null)));
}
// Compile the query
var unifier = new SimpleUnifier();
var assignments = new PredicateAssignmentList();
// Assume we have a basic predicate
foreach (var arg in goal.Dependencies)
{
assignments.AddArgument(arg);
}
// Run through the unifier
var freeVariableNames = unifier.QueryUnifier.Bind(assignments.Assignments);
var freeVariables = freeVariableNames.Select(variable => unifier.GetVariableLocation(variable).Dereference());
unifier.QueryUnifier.Compile(assignments.Assignments);
// Call via the solver
var moveNext = solver.Call(goal.UnificationKey, unifier.GetArgumentVariables(assignments.CountArguments()));
Func <IQueryResult> nextResult = () =>
{
// Update the variables to the next result
var succeeded = moveNext();
// Nothing to do if we didn't succeed
if (!succeeded)
{
return(new BasicQueryResult(false, new EmptyBinding(null)));
}
// Bind the variables
var variableValues = freeVariables
.Select(varRef => varRef.Freeze())
.Zip(freeVariableNames, (value, name) => new { Value = value, Name = name }).ToArray();
var binding = new BasicBinding(null, variableValues.ToDictionary(val => val.Name, val => val.Value));
// Return the result
return(new BasicQueryResult(true, binding));
};
// Chain to produce the final result
return(new ChainedResult(nextResult(), () => Task.FromResult(nextResult())));
}
