Could .NET be parsed and evaluated at runtime

Question

I thought it would be fun if I could write vb.net or c# code at runtime and the interpreter would automatically parse it like python does it, so I made a little program, which would do something similar. Basically it looks like this:

InputArgs = Console.ReadLine()
ParseInput(InputArgs.Split(" "))

Private Sub ParseInput(Args as List(Of String), Optional TempArgs as List(Of String))
Dim arg as string = Args(0)
If arg = ".." then
 ...
elseif arg = ".." then
 ...
end if
End Sub

I know it's not a good system, but it show's the basics. So my question is: Is it possible to make vb.net or c# like python - interpreted at runtime?

You could probably do this with the new [Rosyln CTP](http://blogs.msdn.com/b/csharpfaq/archive/2011/10/19/introducing-the-microsoft-roslyn-ctp.aspx) — Prescott, Nov 30 '11 at 14:56
If you're supposing that it is impossible then what do you think might be the reason for making this impossible? You can do almost everything in programmers world, but some things are not that easy to implement. Anyway, look at [Roslyn](http://blogs.msdn.com/b/visualstudio/archive/2011/10/19/introducing-the-microsoft-roslyn-ctp.aspx) — Snowbear, Nov 30 '11 at 14:56
Look at this question: http://stackoverflow.com/questions/4629/c-sharp-eval-equivalent — hcb, Nov 30 '11 at 14:56
The Workflow Engine (WF4) has a VB expression evaluator. It's only VB and only expressions, and I have no idea if it can be used outside of WF, but you may be able to get it to work for you. — Gabe, Nov 30 '11 at 15:07

sehe · Accepted Answer · 2011-11-30T15:21:56.413

This already exists in a fair number of shapes and forms:

Mono.CSharp

Mono has the Mono.CSharp assembly, which you can reference to do whatever CSharp.exe (A C# 'interpreter' or interactive shell, if you will) can do:

void ReadEvalPrintLoopWith (ReadLiner readline)
{
    string expr = null;
    while (!InteractiveBase.QuitRequested){
            string input = readline (expr == null);
            if (input == null)
                return;

            if (input == "")
                continue;

            expr = expr == null ? input : expr + "\n" + input;

            expr = Evaluate (expr);
    } 
}

Needless to say this works on MS.Net too (of course, that's the point about portable .Net).

Full sources here on github - just as the rest of Mono, in fact.

DLR

Several DLR languages have been implemented, including but not limited to

IronRuby
IronPython
Jint (http://jint.codeplex.com/) - does javascript on .Net 2.0

It will allow you to evaluate python/ruby code on the fly in the .NET framework.

Roslyn

Microsoft has published Roslyn as a CTP (preview). It can basically do the same stuff as the Mono REPL (first item), and (much) more. But it is a preview still.

score 2 · Answer 2 · answered Nov 30 '11 at 14:57

It can be, but it would be a lot of work.

One way would be to write a parser + interpreter yourself. To create the parser, you'd need a grammar definition of the input language, such as C#. The C# grammar is very complex, mind you.

Another way is to dynamically compile C# code. Here is an example of how to do that: http://www.voidspace.org.uk/ironpython/dynamically_compiling.shtml and http://blogs.msdn.com/b/saveenr/archive/2009/08/11/a-walkthrough-of-dynamically-compiling-c-code.aspx.

Good luck!

score 1 · Answer 3 · answered Nov 30 '11 at 15:15

Don't have much time to give you a proper answer, but here is eval code from one of my old projects:

        CSharpCodeProvider c = new CSharpCodeProvider();
        ICodeCompiler icc = c.CreateCompiler();
        CompilerParameters cp = new CompilerParameters();

        cp.ReferencedAssemblies.Add("system.dll");
        cp.ReferencedAssemblies.Add("system.xml.dll");
        cp.ReferencedAssemblies.Add("system.data.dll");
        cp.ReferencedAssemblies.Add("system.windows.forms.dll");
        cp.ReferencedAssemblies.Add("system.drawing.dll");

        cp.CompilerOptions = "/t:library";
        cp.GenerateInMemory = true;

        StringBuilder sb = new StringBuilder("");
        sb.Append("using System;\n");
        sb.Append("using System.Xml;\n");
        sb.Append("using System.Data;\n");
        sb.Append("using System.Data.SqlClient;\n");
        sb.Append("using System.Windows.Forms;\n");
        sb.Append("using System.Drawing;\n");

        sb.Append("namespace CSCodeEvaler{ \n");
        sb.Append("public class CSCodeEvaler{ " + csCode + "} }");

        CompilerResults cr = icc.CompileAssemblyFromSource(cp, sb.ToString());
        if (cr.Errors.Count > 0)
        {
            MessageBox.Show("ERROR: " + cr.Errors[0].ErrorText,
               "Error evaluating cs code", MessageBoxButtons.OK,
               MessageBoxIcon.Error);
            return null;
        }

        System.Reflection.Assembly a = cr.CompiledAssembly;
        object o = a.CreateInstance("CSCodeEvaler.CSCodeEvaler");

        Type t = o.GetType();
        MethodInfo mi = t.GetMethod("Transform");

        return mi;

Original variant of this code was taken from: http://www.codeproject.com/KB/cs/evalcscode.aspx

It compiles some C# code (code should be in csCode variable), then tries to find Transform() method in it and returns its MethodInfo, so we can execute it.

But remember, every time you call this code, a new assembly will be loaded, so don't use it too often.

Also, as Prescott said - try Roslyn

Hope this will help. Sorry that haven't provided code example more specific to your question.

PS. If you want some interactive window, there are third party controls for this (use google to find, because I don't remember exact product names)

score 1 · Answer 4 · edited May 23 '17 at 12:20

1

Are you reinventing LinqPad?

LinqPad is a free ergonomic C#/VB/F# scratchpad that instantly executes any expression, statement block or program with rich output formatting. It's excellent.

If you really want to develop your own, have a look at some of the similar existing questions one two three four...

edited May 23 '17 at 12:20

Community

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answered Dec 01 '11 at 10:29

MarkJ

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score 0 · Answer 5 · answered Nov 30 '11 at 14:56

0

Not that I know.. But as a hack you could make a textarea which has a TextChanged event handler which calls the compiler program (not sure where it is).

answered Nov 30 '11 at 14:56

SBoss

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calling compiler will not help, because interpretation code is usually not compilable. – Snowbear Nov 30 '11 at 14:58

score -1 · Answer 6 · answered Nov 30 '11 at 14:55

-1

So my question is: Is it possible to make vb.net or c# like python - interpreted at runtime?

Sure. Start writing an interpreter for it and then you can interpret it. Start with a nice syntax parser. Then go on from there.

answered Nov 30 '11 at 14:55

TomTom

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Could .NET be parsed and evaluated at runtime

6 Answers6

Mono.CSharp

DLR

Roslyn

Linked