LambdaEvaluator.cs

using System.Threading.Tasks;
using Waher.Script;
using Waher.Script.Abstraction.Elements;
using Waher.Script.Operators;
using Waher.Script.Persistence.SQL;
 
namespace Waher.Persistence.FullTextSearch.PropertyEvaluators
{
    public class LambdaEvaluator : IPropertyEvaluator
    {
        private LambdaDefinition lambda;
        private ObjectProperties variables;
 
        public LambdaEvaluator()
        {
        }
 
        public async Task Prepare(string Definition)
        {
            Expression Exp = new Expression(Definition);
            this.lambda = await Exp.EvaluateAsync(new Variables()) as LambdaDefinition;
        }
 
        public async Task<object> Evaluate(object Instance)
        {
            if (!(this.lambda is null))
            {
                if (this.variables is null)
                    this.variables = new ObjectProperties(Instance, new Variables());
                else
                    this.variables.Object = Instance;
 
                IElement E = await this.lambda.EvaluateAsync(new IElement[] { Expression.Encapsulate(Instance) }, this.variables);
 
                return E.AssociatedObjectValue;
            }
            else
                return null;
        }
    }
}