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Posted 12 Jun 2010

TinyLisp: A Language and Parser to See LINQ Expressions in Action

, 12 Jun 2010
A small program that parses expressions and evaluates them using LINQ Expressions
using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Windows;
using System.Windows.Documents;
using le = System.Linq.Expressions;

namespace TinyLisp {
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window {
        public MainWindow() {

        private void Button_Click(object sender, RoutedEventArgs e) {

            string sExpression = Input.Text;
            try {
                CharStream s = new CharStream(sExpression);
                CodeNode nExpression = new ExpressionNode(s);

                // Show in tree
                List<CodeNode> ln = new List<CodeNode>() { nExpression };
                tvAst.ItemsSource = ln;

                // convert to Linq.Expression
                le.Expression eExpression = nExpression.ToExpression();
                // put it into a Lambda
                le.Expression<Func<int>> lExpression = le.Expression.Lambda<Func<int>>(eExpression);
                // Compile the lambda
                Func<int> fExpression = lExpression.Compile();             
                // display the Linq Expression
                // wrap expression in ExpressionAdapter and then List<ExpressionAdapter> (because a Treeview.ItemSource expects an IEnumerable) and bind TreeView to it
                List<ExpressionAdapter> l = new List<ExpressionAdapter>() { new ExpressionAdapter(lExpression, "Expression") };
                tvExpr.ItemsSource = l;

                // and execute the compiled lambda to see the result
                MessageBox.Show("the answer is " + fExpression(), "That's easy!");

            } catch (Exception ex) { MessageBox.Show(ex.Message, "Hmmm, you might want to check that again"); }



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About the Author

Leaseplan Corporation
Netherlands Netherlands
Gert-Jan is a Senior Quantitative Risk Manager at Leaseplan Corporation. In that job he doesn't get to code much he does these little projects to keep his skills up and feed the inner geek.

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