[IronPython] Determine used SymbolIds in an expression

[Christian Schmidt]

Hi,

I found some answers to my own questions. But I'm stuck again...

> how can I determine the Symbols or SymbolIds that are used in an 
> (IP2-)expression?
> Obviously I need to parse the expression. Where can I find a small 
> sample or tutorial on parsing in IP2?

http://www.ironpython.info/index.php/The_IronPython_2_Parser

Seems that the example is outdated. Here's my try, which compiles, but 
produces NullReferenceException when calling CreateParser and seems very 
complicated to me.

Thanks for any help.

class SymbolWalker : IronPython.Compiler.Ast.PythonWalker
{
   public Dictionary<SymbolId, int> symbols =
     new Dictionary<SymbolId, int>();

   public override bool Walk(NameExpression node) {
     symbols[node.Name] = 1;
     return true;
   }
}


IEnumerable<SymbolId> GetSymbols(string pyExpression)
{
   Microsoft.Scripting.Hosting.ScriptRuntime runtime =
     ScriptRuntime.Create();
   Microsoft.Scripting.Hosting.ScriptEngine scriptEngine =
     runtime.GetEngine("py");
   Microsoft.Scripting.Hosting.ScriptSource src =
     engine.CreateScriptSourceFromString(expression);
   System.Scripting.SourceUnit code =
     Microsoft.Scripting.Hosting.HostingHelpers.GetSourceUnit(src);
   System.Scripting.CompilerOptions opts =
     new System.Scripting.CompilerOptions();
   System.Scripting.ErrorSink sink =
     System.Scripting.ErrorSink.Default;
   Microsoft.Scripting.Compilers.CompilerContext context =
     new Microsoft.Scripting.Compilers.CompilerContext(code, opts, sink);
   IronPython.PythonEngineOptions engineOptions =
     new IronPython.PythonEngineOptions();
   IronPython.Compiler.Parser parser =
     IronPython.Compiler.Parser.CreateParser(context, engineOptions);
   IronPython.Compiler.Ast.Statement stmt
     = parser.ParseTopExpression();
   SymbolWalker walker =
     new SymbolWalker();
   stmt.Walk(walker);
   return walker.symbols.Keys;
}