Wednesday, 21st November 2007

Scripting with .NET is unbelievably easy. grin.gif

I wanted to add scripting support to Brass, and have added it using .NET's excellent powers of reflection and its System.CodeDom.Compiler namespace.

The first thing I need to do is find out which language the source script is written in. I use the extension to check for this.

string ScriptFile = ...; // Name of main script file to compile.

CodeDomProvider Provider = null;

// Get the extension (eg "cs")
string Extension = Path.GetExtension(ScriptFile).ToLowerInvariant();
if (Extension.Length > 0 && Extension[0] == '.') Extension = Extension.Substring(1);

// Hunt through all available compilers and dig out one with a matching extension.
foreach (CompilerInfo Info in CodeDomProvider.GetAllCompilerInfo()) {
	if (Info.IsCodeDomProviderTypeValid) {
		CodeDomProvider TestProvider = Info.CreateProvider();
		if (TestProvider.FileExtension.ToLowerInvariant() == Extension) {
			Provider = TestProvider;

if (Provider == null) throw new CompilerExpection(source, "Script language not supported.");

Now that we have a compiler, we just set some settings, add some references, then compile the source files:

string[] ScriptFiles = ...; // Array of source file name(s) to compile.

// Compiler settings:
CompilerParameters Parameters = new CompilerParameters();
Parameters.GenerateExecutable = false; // Class lib, not .exe
Parameters.GenerateInMemory = true;

// Add references:

// Compile!
CompilerResults Results = Provider.CompileAssemblyFromFile(Parameters, ScriptFiles);

And that's it! In my case I now pass any errors back up to the assembler, and exit if there were any errors:

// Errors?
foreach (CompilerError Error in Results.Errors) {
	Compiler.NotificationEventArgs Notification = new Compiler.NotificationEventArgs(compiler, Error.ErrorText, Error.FileName, Error.Line);
	if (Error.IsWarning) {
	} else {

// Do nothing if there were errors.
if (Results.Errors.HasErrors) return;

Now the task is passed on to reflection; I go through the compiled assembly, hunt down methods and wrap them up for use as native Brass functions and/or directives.

// Grab the public classes from the script.
foreach (Type T in Results.CompiledAssembly.GetExportedTypes()) {
    // ...

I've used this technique in the release of my PAL demo; a C# script file is used to encode an image to the 18×304 resolution and format required by the routine.

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