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Posted 22 Oct 2011
Licenced MIT

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.Reflection;

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

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

        public Type ToType(Node node)
            return Utilities.GetType(node.Text.Trim());
        public Expression ToExpr(Node n)
            switch (n.Label)
                case "Expr":
                    return ToExpr(n[0]);
                case "TertiaryExpr":
                    if (n.Count > 1)
                        return Expression.Condition(ToExpr(n[0]), ToExpr(n[1]), ToExpr(n[2]));
                        return ToExpr(n[0]);    
                case "AssignExpr":
                    throw new NotImplementedException();
                case "BinaryExpr":
                    if (n.Count > 1)
                        return CreateBinaryExpression(n[1].Text, ToExpr(n[0]), ToExpr(n[2]));
                        return ToExpr(n[0]);
                case "UnaryExpr":
                        var x = ToExpr(n[0]);
                        for (int i = 1; i < n.Count; ++i)
                            switch (n[i].Label)
                                case "Inc":         
                                    x = Expression.Increment(x); 
                                case "Dec":         
                                    x = Expression.Decrement(x); 
                                case "Indexer":     
                                    x = Expression.ArrayIndex(x, ToExpr(n[i][0])); 
                                case "ArgList":
                                    x = Expression.Invoke(x, n[1].Nodes.Select(ToExpr)); 
                                case "Selector":    
                                    x = Expression.Field(x, n[i][0].Text); 
                                    throw new Exception("Unrecognized postfix operator " + n[i].Label);
                        return x;
                case "PrefixExpr":
                    if (n[0].Label == "LeafExpr") 
                        return ToExpr(n[0]);
                    switch (n[0].Text)
                        case "++":  
                            return Expression.PreIncrementAssign(ToExpr(n[1]));                                
                        case "--":  
                            return Expression.PreDecrementAssign(ToExpr(n[1]));
                        case "!":   
                            return Expression.Not(ToExpr(n[1]));
                        case "-":   
                            return Expression.Negate(ToExpr(n[1]));
                        case "~":   
                            return Expression.OnesComplement(ToExpr(n[1]));
                            throw new Exception("Unrecognized prefix operator " + n[0].Text);
                case "LeafExpr":
                    return ToExpr(n[0]);
                case "ParenthesizedExpr":
                    return ToExpr(n[0]);
                case "NewExpr":
                    throw new NotImplementedException();
                case "Identifier":
                    return Lookup(n.Text);
                case "Integer":
                    return Expression.Constant(Int32.Parse(n.Text));
                case "Float":
                    return Expression.Constant(Double.Parse(n.Text));
                case "String":
                    return Expression.Constant(n.Text.StripQuotes());
                case "UntypedLambdaParam":
                    return Expression.Parameter(typeof(Object), n[0].Text);
                case "TypedLambdaParam":
                    return Expression.Parameter(Utilities.GetType(n[0].Text), n[1].Text);
                case "LambdaExpr":
                    var ps = n[0].Nodes.Select(ToExpr).OfType<ParameterExpression>();
                    if (n[1].Label == "Block")
                        return CreateStatementLambda(ps, () => ToExpr(n[1]));
                        return CreateExpressionLambda(ps, () => ToExpr(n[1]));
                case "Block":
                    return ScopedExpr(() => Expression.Block(n.Nodes.Select(ToExpr)));
                case "ExprStatement":
                    return Expression.Block(ToExpr(n[0]));
                case "ReturnStatement":
                    if (n.Count > 0)
                        return Expression.Return(GetReturnTarget(), Expression.Constant(null)); else
                        return Expression.Return(GetReturnTarget(), ToExpr(n[0]));
                case "Statement":
                    return ToExpr(n[0]);
                    throw new Exception("Node type not handled " + n.Label);

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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.

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