/// <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())));
}
/// <summary>
/// Solves a subclause
/// </summary>
private Func <bool> SolveSubclause(AssignmentData clause, SimpleUnifier unifier, Func <bool> solvePreviousClause)
{
// Create a new trail
unifier.PushTrail();
Func <bool> nextInThisClause = null;
return(() =>
{
if (nextInThisClause == null || !nextInThisClause())
{
// Reset the state and get the solution for the previous clause
unifier.ResetTrail();
if (!solvePreviousClause())
{
return false;
}
// Push a new trail for this clause
unifier.PushTrail();
// Solve this clause
unifier.QueryUnifier.Bind(clause.Assignments);
if (!unifier.QueryUnifier.Compile(clause.Assignments))
{
return false;
}
// Call the predicate
nextInThisClause = _subclauseSolver.Call(clause.PredicateName, unifier.GetArgumentVariables(clause.NumArguments));
// Result depends on the next item in this clause
return nextInThisClause();
}
else
{
// nextInThisClause() returned true, so this clause was solved
return true;
}
});
}