ConcatEvaluator.cs

using System.Text;
using Waher.Script.Abstraction.Elements;
using Waher.Script.Model;
using Waher.Script.Objects;
 
namespace Waher.Script.Functions.Strings
{
    public class ConcatEvaluator : UnaryIterativeEvaluator
    {
        private readonly string delimiter;
        private readonly bool hasDelimiter;
        private StringBuilder sb = null;
 
        public ConcatEvaluator(Concat Node)
            : base(Node.Arguments[0])
        {
            if (Node.Arguments.Length == 2 && Node.Arguments[1] is ConstantElement C)
            {
                this.delimiter = ScriptNode.ToString(C.Constant);
                this.hasDelimiter = !string.IsNullOrEmpty(this.delimiter);
            }
            else
            {
                this.delimiter = null;
                this.hasDelimiter = false;
            }
        }
 
        public override void RestartEvaluator()
        {
            this.sb = null;
        }
 
        public override void AggregateElement(IElement Element)
        {
            if (this.sb is null)
                this.sb = new StringBuilder();
            else if (this.hasDelimiter)
                this.sb.Append(this.delimiter);
 
            this.sb.Append(ScriptNode.ToString(Element));
        }
 
        public override IElement GetAggregatedResult()
        {
            return new StringValue(this.sb?.ToString() ?? string.Empty);
        }
    }
}