Translate C# code into AST?

Question

Is it currently possible to translate C# code into an Abstract Syntax Tree?

Edit: some clarification; I don't necessarily expect the compiler to generate the AST for me - a parser would be fine, although I'd like to use something "official." Lambda expressions are unfortunately not going to be sufficient given they don't allow me to use statement bodies, which is what I'm looking for.

Answer 1

The Roslyn project is in Visual Studio 2010 and gives you programmatic access to the Syntax Tree, among other things.

SyntaxTree tree = SyntaxTree.ParseCompilationUnit(
    @" C# code here ");
var root = (CompilationUnitSyntax)tree.Root;

Answer 2

Is it currently possible to translate C# code into an Abstract Syntax Tree?

Yes, trivially in special circumstances (= using the new Expressions framework):

// Requires 'using System.Linq.Expressions;'
Expression<Func<int, int>> f = x => x * 2;

This creates an expression tree for the lambda, i.e. a function taking an int and returning the double. You can modify the expression tree by using the Expressions framework (= the classes from in that namespace) and then compile it at run-time:

var newBody = Expression.Add(f.Body, Expression.Constant(1));
f = Expression.Lambda<Func<int, int>>(newBody, f.Parameters);
var compiled = f.Compile();
Console.WriteLine(compiled(5)); // Result: 11

Notice that all expressions are immutable so they have to be built anew by composition. In this case, I've prepended an addition of 1.

Notice that these expression trees only work on real expressions i.e. content found in a C# function. You can't get syntax trees for higher constructs such as classes this way. Use the CodeDom framework for these.

Answer 3

Check out .NET CodeDom support. There is an old article on code project for a C# CodeDOM parser, but it won't support the new language features.

There is also supposed to be support in #develop for generating a CodeDom tree from C# source code according to this posting.

Answer 4

There is much powerful than R# project. Nemerle.Peg:

https://code.google.com/p/nemerle/source/browse/nemerle/trunk/snippets/peg-parser/

And it has C# Parser which parsers all C# code and translates it to AST !

https://code.google.com/p/nemerle/source/browse/nemerle/trunk/snippets/csharp-parser/

You can download installer here: https://code.google.com/p/nemerle/

Answer 5

Personally, I would use NRefactory, which is free, open source and gains popularity.

Answer 6

It looks like this sort of functionality will be included with whatever comes after C# 4, according to Anders Hejlsberg's 'Future of C#' PDC video.

Answer 7

The ANTLR Parser Generator has a grammar for C# 3.0 which covers everything except for LINQ syntax.

Answer 8

I've just answered on another thread here at StackOverflow a solution where I implemented an API to create and manipulate AST from C# Source Code

Answer 9

It is strange that nobody suggested hacking the existing Mono C# compiler.

Answer 10

Our C# front end for DMS parses full C# 3.0 including LINQ and produces ASTs. DMS in fact is an ecosystem for analyzing/transforming source code using ASTs for front-end provided langauges.

EDIT 3/10/2010: ... Now handles full C# 4.0

EDIT: 6/27/2014: Handles C# 5.0 since quite awhile.

EDIT: 6/15/2016: Handles C# 6.0. See https://stackoverflow.com/a/37847714/120163 for a sample AST.

Answer 11

ANTLR is not very useful. LINQ is not what you want.

Try Mono.Cecil! http://www.mono-project.com/Cecil

It is used in many projects, including NDepend! http://www.ndepend.com/

Answer 12

Please see the R# project (sorry the docs are in Russian, but there are some code examples). It allows AST manipulations on C# code.

http://www.rsdn.ru/projects/rsharp/article/rsharp_mag.xml

Project's SVN is here: (URL updated, thanks, derigel)

Also please see the Nemerle language. It is a .Net language with strong support for metaprogramming.