public IEnumerable <IDebugEvent> Solve (Compiled.Goal [] goalDefs)
{
// Instantiate the goals.
var queryArgumentInstantiator = new ArgumentInstantiator();
var goals = InstantiateGoals (goalDefs, queryArgumentInstantiator);
frame = new Frame (goals, null, new BoundVariableSet (), queryArgumentInstantiator.Variables);
// ReSharper disable ConditionIsAlwaysTrueOrFalse
while (frame != null)
// ReSharper restore ConditionIsAlwaysTrueOrFalse
{
if (frame.GoalsProven == frame.Goals.Length)
{
// No more goals to prove or it's a fact.
System.Diagnostics.Debug.Assert (frame.Goals.All (g => g.CurrentFrame != null));
if (frame.Parent == null)
{
yield return new Solution (frame);
foreach (var e in GoToLastChoicePoint ())
yield return e;
}
else
{
// go on and prove the next parent goal.
frame = frame.Parent;
frame.GoalsProven++;
}
continue;
}
var goal = frame.Goals [frame.GoalsProven];
// Check that the same goal is not on the stack to prevent infinite loops.
if (AlreadyOnTheStack (goal))
{
foreach (var e in Backtrack ())
yield return e;
}
else
{
var newFrame = goal.GetNextFrame ();
if (newFrame == null)
{
foreach (var e in Backtrack ())
yield return e;
}
else
{
yield return new Enter (newFrame);
frame = newFrame; // decend the tree
}
}
}
}
IEnumerable <IDebugEvent> Backtrack ()
{
// Current frame's current goal does not unify with any (more) clauses.
if (frame.GoalsProven == 0)
{
if (frame.Parent != null)
yield return new Leave (frame);
frame = frame.Parent; // ascend the tree; frame may become null at this point.
}
else
{
frame.CurrentGoal.Restart();
foreach (var e in GoToLastChoicePoint ())
yield return e;
}
}
IEnumerable <IDebugEvent> GoToLastChoicePoint ()
{
while (frame.Goals.Length > 0)
{
frame.GoalsProven--;
var lastProvenGoal = frame.CurrentGoal;
frame = lastProvenGoal.CurrentFrame;
}
yield return new Leave (frame);
frame = frame.Parent; // ascend the tree; frame CANNOT become null at this point.
}
