private static Goal CreateGoal(ArgumentInstantiator visitor, Compiled.Goal goalDef)
{
var arguments = goalDef.Arguments.Select(a => a.Accept(visitor)).ToArray();
var predicate = goalDef.Predicate;
var goal = predicate.Accept(new GoalInstantiator());
goal.Arguments = arguments;
goal.Definition = goalDef;
goal.Restart();
return(goal);
}
Frame Unify(Compiled.Clause clause)
{
var boundVariables = new BoundVariableSet();
var argumentInstantiator = new ArgumentInstantiator();
var clauseHeadArguments = clause.Head.Arguments.Select(a => a.Accept(argumentInstantiator)).ToArray();
if (boundVariables.ZipUnify(Arguments, clauseHeadArguments))
{
Goal [] goals = EngineInternals.InstantiateGoals(clause.Body, argumentInstantiator);
return(new Frame(goals, this, boundVariables, argumentInstantiator.Variables));
}
return(null);
}
// ReSharper disable ParameterTypeCanBeEnumerable.Global
internal static Goal [] InstantiateGoals(Compiled.Goal [] goalDefs, ArgumentInstantiator argumentInstantiator)
// ReSharper restore ParameterTypeCanBeEnumerable.Global
{
return(goalDefs.Select(goalDef => CreateGoal(argumentInstantiator, goalDef)).ToArray());
}
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
}
}
}
}