ExpressionTreeTranslationSampleTwo.cs

using System.Linq.Expressions;

namespace ExpressionTreeSamples;

public class ExpressionTreeTranslationSampleTwo : Sample
{
    public override string Name { get; } = "Translation Expression Trees, Sample 2: Computing the sum of an addition tree";

    public override void Run()
    {
        var one = Expression.Constant(1, typeof(int));
        var two = Expression.Constant(2, typeof(int));
        var three = Expression.Constant(3, typeof(int));
        var four = Expression.Constant(4, typeof(int));
        var addition = Expression.Add(one, two);
        var add2 = Expression.Add(three, four);
        var sum = Expression.Add(addition, add2);

        // Declare the delegate, so we can call it
        // from itself recursively:
        Func<Expression, int> aggregate = null!;
        // Aggregate, return constants, or the sum of the left and right operand.
        // Major simplification: Assume every binary expression is an addition.
        aggregate = (exp) =>
            exp.NodeType == ExpressionType.Constant ?
            (int)((ConstantExpression)exp).Value :
            aggregate(((BinaryExpression)exp).Left) + aggregate(((BinaryExpression)exp).Right);

        var theSum = aggregate(sum);
        Console.WriteLine(theSum);
    }
}