Is.cs

using System;
using System.Reflection;
using System.Threading.Tasks;
using Waher.Script.Abstraction.Elements;
using Waher.Script.Exceptions;
using Waher.Script.Model;
using Waher.Script.Objects;
 
namespace Waher.Script.Operators.Membership
{
    public class Is : BinaryScalarOperator
    {
        public Is(ScriptNode Left, ScriptNode Right, int Start, int Length, Expression Expression)
            : base(Left, Right, Start, Length, Expression)
        {
        }
 
        public override IElement Evaluate(IElement Left, IElement Right, Variables Variables)
        {
            if (Right is TypeValue TypeValue)
                return this.EvaluateIs(Left, TypeValue);
            else
                return base.Evaluate(Left, Right, Variables);
        }
 
        private BooleanValue EvaluateIs(IElement Left, TypeValue Right)
        {
            Type Expected = Right.Value;
            object Obj = Left.AssociatedObjectValue;
            Type Candidate = Obj?.GetType() ?? typeof(object);
 
            if (Expected.GetTypeInfo().IsAssignableFrom(Candidate.GetTypeInfo()))
                return BooleanValue.True;
            else
                return BooleanValue.False;
        }
 
        public override Task<IElement> EvaluateAsync(IElement Left, IElement Right, Variables Variables)
        {
            if (Right is TypeValue TypeValue)
                return Task.FromResult<IElement>(this.EvaluateIs(Left, TypeValue));
            else
                return base.EvaluateAsync(Left, Right, Variables);
        }
 
        public override IElement EvaluateScalar(IElement Left, IElement Right, Variables Variables)
        {
            if (Right is TypeValue TypeValue)
                return this.EvaluateIs(Left, TypeValue);
            else
                throw new ScriptRuntimeException("Right operand in an IS operation must be a type value.", this);
        }
 
        public override Task<IElement> EvaluateScalarAsync(IElement Left, IElement Right, Variables Variables)
        {
            if (Right is TypeValue TypeValue)
                return Task.FromResult<IElement>(this.EvaluateIs(Left, TypeValue));
            else
                throw new ScriptRuntimeException("Right operand in an IS operation must be a type value.", this);
        }
 
        public override UpgradeBehaviour ScalarUpgradeBehaviour => UpgradeBehaviour.DifferentTypesOk;
    }
}