NullCheck.cs

using System;
using System.Threading.Tasks;
using Waher.Script.Abstraction.Elements;
using Waher.Script.Model;
 
namespace Waher.Script.Operators.Conditional
{
    public class NullCheck : BinaryScalarOperator
    {
        public NullCheck(ScriptNode Left, ScriptNode Right, int Start, int Length, Expression Expression)
            : base(Left, Right, Start, Length, Expression)
        {
        }
 
        public override IElement Evaluate(Variables Variables)
        {
            IElement Left;
 
            try
            {
                Left = this.left.Evaluate(Variables);
            }
            catch (Exception)
            {
                return this.right.Evaluate(Variables);
            }
 
            if (!(Left.AssociatedObjectValue is null))
                return Left;
 
            IElement Right = this.right.Evaluate(Variables);
 
            return this.Evaluate(Left, Right, Variables);
        }
 
        public override async Task<IElement> EvaluateAsync(Variables Variables)
        {
            IElement Left;
 
            try
            {
                Left = await this.left.EvaluateAsync(Variables);
            }
            catch (Exception)
            {
                return await this.right.EvaluateAsync(Variables);
            }
 
            if (!(Left.AssociatedObjectValue is null))
                return Left;
 
            IElement Right = await this.right.EvaluateAsync(Variables);
 
            return await this.EvaluateAsync(Left, Right, Variables);
        }
 
        public override IElement EvaluateScalar(IElement Left, IElement Right, Variables Variables)
        {
            if (Left.AssociatedObjectValue is null)
                return Right;
            else
                return Left;
        }
 
        public override UpgradeBehaviour ScalarUpgradeBehaviour => UpgradeBehaviour.DifferentTypesOk;
    }
}