PreDecrement.cs

using System;
using System.Collections.Generic;
using Waher.Script.Abstraction.Elements;
using Waher.Script.Exceptions;
using Waher.Script.Model;
using Waher.Script.Objects;
 
namespace Waher.Script.Operators.Assignments.Pre
{
    public class PreDecrement : ScriptLeafNodeVariableReference
    {
        public PreDecrement(string VariableName, int Start, int Length, Expression Expression)
            : base(VariableName, Start, Length, Expression)
        {
        }
 
        public override IElement Evaluate(Variables Variables)
        {
            if (!Variables.TryGetVariable(this.variableName, out Variable v))
                throw new ScriptRuntimeException("Variable not found: " + this.variableName, this);
 
            IElement Value = v.ValueElement;
 
            if (Value.AssociatedObjectValue is double d)
                Value = new DoubleNumber(d - 1);
            else
                Value = Decrement(Value, this);
 
            Variables[this.variableName] = Value;
 
            return Value;
        }
 
        public static IElement Decrement(IElement Value, ScriptNode Node)
        {
            if (Value is ICommutativeRingWithIdentityElement e)
                return Arithmetics.Subtract.EvaluateSubtraction(Value, e.One, Node);
            else if (Value.IsScalar)
                throw new ScriptRuntimeException("Unable to decrement variable.", Node);
            else
            {
                LinkedList<IElement> Elements = new LinkedList<IElement>();
 
                foreach (IElement Element in Value.ChildElements)
                    Elements.AddLast(Decrement(Element, Node));
 
                return Value.Encapsulate(Elements, Node);
            }
        }
 
    }
}