PopFirst.cs

using System.Collections.Generic;
using Waher.Runtime.Collections;
using Waher.Script.Abstraction.Elements;
using Waher.Script.Model;
using Waher.Script.Objects;
 
namespace Waher.Script.Functions.Vectors
{
    public class PopFirst : FunctionOneVectorVariable
    {
        private readonly VariableReference reference;
 
        public PopFirst(ScriptNode Argument, int Start, int Length, Expression Expression)
            : base(Argument, Start, Length, Expression)
        {
            this.reference = Argument as VariableReference;
        }
 
        public override string FunctionName => nameof(PopFirst);
 
        public override IElement EvaluateVector(IVector Argument, Variables Variables)
        {
            int c = Argument.Dimension;
            if (c == 0)
                return ObjectValue.Null;
 
            IElement Result = Argument.GetElement(0);
 
            if (!(this.reference is null))
            {
                ICollection<IElement> Elements = Argument.VectorElements;
 
                if (!Elements.Remove(Result))
                {
                    ChunkedList<IElement> Elements2 = new ChunkedList<IElement>();
                    bool First = true;
 
                    foreach (IElement E in Elements)
                    {
                        if (First)
                            First = false;
                        else
                            Elements2.Add(E);
                    }
 
                    Variables[this.reference.VariableName] = Argument.Encapsulate(Elements2, this);
                }
                else
                    Variables[this.reference.VariableName] = Argument.Encapsulate(Elements, this);
            }
 
            return Result;
        }
 
    }
}