Click here to Skip to main content
13,297,266 members (64,384 online)
Click here to Skip to main content


248 bookmarked
Posted 22 Oct 2011

Implementing Programming Languages Using C# 4.0

, 12 Jul 2012
An introduction to creating programming language tools using C# 4.0.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Linq.Expressions;
using System.Dynamic;
using System.Reflection;

namespace Diggins.Jigsaw
    public class SchemeExpressionCompiler : ExpressionCompiler
        public static Delegate CompileLambda(string s)
            var nodes = SchemeGrammar.Lambda.Parse(s);
            return CompileLambda(nodes[0]);

        public static Delegate CompileLambda(Node n)
            var compiler = new SchemeExpressionCompiler();
            var expr = (LambdaExpression)compiler.ToExpr(n);
            if (expr == null) return null;
            return expr.Compile();

        public Expression SExprToExpr(Node node)
            var terms = node["Terms"];
            var head = terms[0];
            var mi = typeof(Primitives).GetMethod(head.Text);
            if (mi == null) throw new Exception("Could not find primitive named " + head.Text);
            var args = terms.Nodes.Skip(1).Select(n => ToExpr(n));
            return Expression.Call(mi, args);

        public Expression LetToExpr(Node node)
            var exprs = new List<Expression>();
            foreach (var binding in node[0].Nodes) {
                var name = binding[0].Text;
                var param = AddBinding(Expression.Parameter(typeof(Object), name));
                exprs.Add(Expression.Assign(Lookup(name), ToExpr(binding[1])));
            return Expression.Block(exprs);

        public Expression ToExpr(Node node)
            switch (node.Label)
                case "Integer":
                    return Expression.Constant(int.Parse(node.Text));
                case "Float":
                    return Expression.Constant(double.Parse(node.Text));
                case "String":
                    return Expression.Constant(node.Text.Substring(1, node.Text.Length - 2));
                case "SExpr":
                    return SExprToExpr(node);
                case "Symbol":
                    return Lookup(node.Text);
                case "Param":
                    return Expression.Parameter(typeof(Object), node[0].Text);
                case "Term":
                    return ToExpr(node[0]);
                case "Atom":
                    return ToExpr(node[0]);
                case "Lambda":
                    return CreateExpressionLambda(node["ParamList"].Nodes.Select(ToExpr)
                        .OfType<ParameterExpression>().ToArray(), () => ToExpr(node["Term"]));
                case "Begin":
                    return Expression.Block(node.Nodes.Select(n => ToExpr(n)));
                case "Let":
                    return LetToExpr(node);
                case "If":
                    return node.Count == 3 
                        ? Expression.IfThenElse(ToExpr(node[0]), ToExpr(node[1]), ToExpr(node[2]))
                        : Expression.IfThen(ToExpr(node[0]), ToExpr(node[1]));
                    throw new Exception("Unrecognized node type " + node.Label);

By viewing downloads associated with this article you agree to the Terms of Service and the article's licence.

If a file you wish to view isn't highlighted, and is a text file (not binary), please let us know and we'll add colourisation support for it.


This article, along with any associated source code and files, is licensed under The MIT License


About the Author

Christopher Diggins
Software Developer Autodesk
Canada Canada
This article was written by Christopher Diggins, a computer science nerd who currently works at Autodesk as an SDK specialist.

You may also be interested in...

Permalink | Advertise | Privacy | Terms of Use | Mobile
Web04 | 2.8.171207.1 | Last Updated 12 Jul 2012
Article Copyright 2011 by Christopher Diggins
Everything else Copyright © CodeProject, 1999-2017
Layout: fixed | fluid