OptionalPattern.cs

using System.Collections.Generic;
using System.Threading.Tasks;
using Waher.Content.Semantic;
 
namespace Waher.Script.Persistence.SPARQL.Patterns
{
    public class OptionalPattern : BinaryOperatorPattern
    {
        public OptionalPattern(ISparqlPattern Left, ISparqlPattern Right)
            : base(Left, Right)
        {
        }
 
        public override async Task<IEnumerable<Possibility>> Search(ISemanticCube Cube, 
            Variables Variables, IEnumerable<Possibility> ExistingMatches, SparqlQuery Query)
        {
            ExistingMatches = await this.Left.Search(Cube, Variables, ExistingMatches, Query);
            if (ExistingMatches is null)
                return null;
 
            LinkedList<Possibility> NewMatches2 = new LinkedList<Possibility>();
 
            foreach (Possibility P in ExistingMatches)
            {
                IEnumerable<Possibility> NewMatches = await this.Right.Search(Cube, Variables,
                    new Possibility[] { P }, Query);
 
                if (NewMatches is null)
                    NewMatches2.AddLast(P);
                else
                {
                    foreach (Possibility P2 in NewMatches)
                        NewMatches2.AddLast(P2);
                }
            }
 
            return NewMatches2;
        }
    }
}