Parameter Substitution within Expression Trees

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;
using System.Windows.Data;
using System.Linq.Expressions;
using ExpressionModifier;

namespace SimplePlots
{
    public partial class MainPage : UserControl
    {
        public const double AXIS_LENGTH = 500d;
        public const double AXIS_UNIT = 25d;

        public MainPage()
        {
            InitializeComponent();

            YAxis.Y2 = AXIS_LENGTH;
            XAxis.X2 = AXIS_LENGTH;
            XMarks.Width = AXIS_LENGTH;
            YMarks.Height = AXIS_LENGTH;

            SetAxes();
            
            // uncomment the two lines below for a sinusoidal example
            PlotMainAndModified(x => Math.Sin(-x), x => x * 2 + 3, 0.01, 10d);
            AddPlot(Colors.Yellow, 0.01, x =>Math.Sin(-(x * 2 + 3)), 3d);

            /*
            // uncomment the two lines below for a parabola example
            PlotMainAndModified(x => x * x, x => x * x - 2, 0.01, 10d);
            AddPlot(Colors.Yellow, 0.01, x => (x * x - 2) * (x * x - 2), 3d);
            */
        }

        public void PlotMainAndModified(Expression<Func<double, double>> mainExpression, Expression<Func<double, double>> substExpression, double delta = 0.1, double pointSize = POINT_SIZE)
        {
            AddPlot(Colors.Red, delta, mainExpression.Compile(), pointSize);

            LambdaExpression modifiedExpression =
                mainExpression.Substitute("x", substExpression);

            AddPlot(Colors.Blue, 0.01, modifiedExpression.Compile() as Func<double, double>, pointSize);
        }

        void SetAxes()
        {
            XMarks.Children.Clear();
            YMarks.Children.Clear();

            int currentNumber = (int) -(AXIS_LENGTH / AXIS_UNIT) / 2;

            for (double x = 0; x <= AXIS_LENGTH; x += AXIS_UNIT)
            {
                Line xMark =
                    new Line
                    {
                        Stroke = new SolidColorBrush(Colors.Black),
                        StrokeThickness = 1,
                        X1 = x,
                        Y1 = -5,
                        X2 = x,
                        Y2 = 0
                    };

                TextBlock xTextBlock = new TextBlock { Text = "" + currentNumber };
                Canvas.SetLeft(xTextBlock, x - 5);

                XMarks.Children.Add(xMark);
                XMarks.Children.Add(xTextBlock);

                double y = AXIS_LENGTH - x;
                Line yMark =
                    new Line
                    {
                        Stroke = new SolidColorBrush(Colors.Black),
                        StrokeThickness = 1,
                        X1 = 5,
                        Y1 = y,
                        X2 = 0,
                        Y2 = y
                    };

                TextBlock yTextBlock = new TextBlock { Text = "" + currentNumber };
                Canvas.SetTop(yTextBlock, y - 10);
                Canvas.SetLeft(yTextBlock, -17);

                YMarks.Children.Add(yMark);
                YMarks.Children.Add(yTextBlock);

                currentNumber++;
            }
        }
                    
        const double POINT_SIZE = 5;

        void AddPoint(double x, double y, Color color, double pointSize = POINT_SIZE)
        {

            Ellipse point = 
                new Ellipse 
                { 
                    Fill = new SolidColorBrush(color),
                    Width = pointSize,
                    Height = pointSize 
                };

            Canvas.SetLeft(point, x * 25 - pointSize / 2d);
            Canvas.SetTop(point, -y * 25 - pointSize / 2d);

            Plots.Children.Add(point);
        }

        public void AddPlot(Color color, double delta, Func<double, double> function, double pointSize)
        {
            double minX = -(AXIS_LENGTH / AXIS_UNIT) / 2;
            double maxX = -minX;

            for (double currentX = minX; currentX <= maxX; currentX += delta)
            {
                try
                {
                    double y = function(currentX);
                    AddPoint(currentX, y, color, pointSize);
                }
                catch
                {
                    
                }
            }
        }
    }
}