/// <summary>
/// Returns a function that solves a list of subclauses
/// </summary>
private Func <bool> SolveAllSubclauses(IEnumerable <AssignmentData> assignments, SimpleUnifier unifier)
{
// The first solution is always true once
bool solvedOnce = false;
Func <bool> solve = () =>
{
if (solvedOnce)
{
// Reset the unifier to its original state and give up
unifier.ResetTrail();
return(false);
}
else
{
solvedOnce = true;
return(true);
}
};
// Chain the solutions for each subclause to generate the final result
foreach (var clause in assignments)
{
solve = SolveSubclause(clause, unifier, solve);
}
// This generates the result
return(solve);
}
/// <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;
}
});
}