source: stable/HeuristicLab.ExtLibs/HeuristicLab.NRefactory/5.5.0/NRefactory.CSharp-5.5.0/Parser/mcs/eval.cs @ 18242

//
// eval.cs: Evaluation and Hosting API for the C# compiler
//
// Authors:
//   Miguel de Icaza (miguel@gnome.org)
//   Marek Safar (marek.safar@gmail.com)
//
// Dual licensed under the terms of the MIT X11 or GNU GPL
//
// Copyright 2001, 2002, 2003 Ximian, Inc (http://www.ximian.com)
// Copyright 2004-2011 Novell, Inc
// Copyright 2011 Xamarin Inc
//

using System;
using System.Threading;
using System.Collections.Generic;
using System.Reflection;
using System.Reflection.Emit;
using System.IO;
using System.Text;
using System.Linq;

namespace Mono.CSharp
{

  /// <summary>
  /// Experimental!
  /// </summary>
  public delegate void ValueModificationHandler (string variableName, int row, int column, object value);

  /// <summary>
  ///   Evaluator: provides an API to evaluate C# statements and
  ///   expressions dynamically.
  /// </summary>
  /// <remarks>
  ///   This class exposes static methods to evaluate expressions in the
  ///   current program.
  ///
  ///   To initialize the evaluator with a number of compiler
  ///   options call the Init(string[]args) method with a set of
  ///   command line options that the compiler recognizes.
  ///
  ///   To interrupt execution of a statement, you can invoke the
  ///   Evaluator.Interrupt method.
  /// </remarks>
  public class Evaluator {

    enum ParseMode {
      // Parse silently, do not output any error messages
      Silent,

      // Report errors during parse
      ReportErrors,

      // Auto-complete, means that the tokenizer will start producing
      // GETCOMPLETIONS tokens when it reaches a certain point.
      GetCompletions
    }

    static object evaluator_lock = new object ();
    static volatile bool invoking;
    
#if !STATIC
    static int count;
#endif
    static Thread invoke_thread;

    readonly Dictionary<string, Tuple<FieldSpec, FieldInfo>> fields;

    Type base_class;
    bool inited;
    int startup_files;

    readonly CompilerContext ctx;
    readonly ModuleContainer module;
    readonly ReflectionImporter importer;
    readonly CompilationSourceFile source_file;

    int? listener_id;
    
    public Evaluator (CompilerContext ctx)
    {
      this.ctx = ctx;

      module = new ModuleContainer (ctx);
      module.Evaluator = this;

      source_file = new CompilationSourceFile (module, null);
      module.AddTypeContainer (source_file);

      startup_files = ctx.SourceFiles.Count;

      // FIXME: Importer needs this assembly for internalsvisibleto
      module.SetDeclaringAssembly (new AssemblyDefinitionDynamic (module, "evaluator"));
      importer = new ReflectionImporter (module, ctx.BuiltinTypes);

      InteractiveBaseClass = typeof (InteractiveBase);
      fields = new Dictionary<string, Tuple<FieldSpec, FieldInfo>> ();
    }

    void Init ()
    {
      var loader = new DynamicLoader (importer, ctx);

      RootContext.ToplevelTypes = module;

      //var startup_files = new List<string> ();
      //foreach (CompilationUnit file in Location.SourceFiles)
      //    startup_files.Add (file.Path);

      loader.LoadReferences (module);
      ctx.BuiltinTypes.CheckDefinitions (module);
      module.InitializePredefinedTypes ();

      inited = true;
    }

    void ParseStartupFiles ()
    {
      Driver d = new Driver (ctx);

      Location.Initialize (ctx.SourceFiles);

      var parser_session = new ParserSession ();
      for (int i = 0; i < startup_files; ++i) {
        var sf = ctx.SourceFiles [i];
        d.Parse (sf, module, parser_session, ctx.Report);
      }
    }

    void Reset ()
    {
      Location.Reset ();
      Location.Initialize (ctx.SourceFiles);
    }

    /// <summary>
    /// When set evaluator will automatically wait on Task of async methods. When not
    /// set it's called responsibility to handle Task execution
    /// </summary>
    public bool WaitOnTask { get; set; }

    /// <summary>
    ///   If true, turns type expressions into valid expressions
    ///   and calls the describe method on it
    /// </summary>
    public bool DescribeTypeExpressions;

    /// <summary>
    ///   Whether the evaluator will use terse syntax, and the semicolons at the end are optional
    /// </summary>
    public bool Terse = true;

    /// <summary>
    ///   The base class for the classes that host the user generated code
    /// </summary>
    /// <remarks>
    ///
    ///   This is the base class that will host the code
    ///   executed by the Evaluator.  By default
    ///   this is the Mono.CSharp.InteractiveBase class
    ///   which is useful for interactive use.
    ///
    ///   By changing this property you can control the
    ///   base class and the static members that are
    ///   available to your evaluated code.
    /// </remarks>
    public Type InteractiveBaseClass {
      get {
        return base_class;
      }
      set {
        base_class = value;

        if (value != null && typeof (InteractiveBase).IsAssignableFrom (value))
          InteractiveBase.Evaluator = this;
      }
    }

    /// <summary>
    ///   Interrupts the evaluation of an expression executing in Evaluate.
    /// </summary>
    /// <remarks>
    ///   Use this method to interrupt long-running invocations.
    /// </remarks>
    public void Interrupt ()
    {
      if (!inited || !invoking)
        return;
      
      if (invoke_thread != null)
        invoke_thread.Abort ();
    }

    /// <summary>
    ///   Compiles the input string and returns a delegate that represents the compiled code.
    /// </summary>
    /// <remarks>
    ///
    ///   Compiles the input string as a C# expression or
    ///   statement, unlike the Evaluate method, the
    ///   resulting delegate can be invoked multiple times
    ///   without incurring in the compilation overhead.
    ///
    ///   If the return value of this function is null,
    ///   this indicates that the parsing was complete.
    ///   If the return value is a string it indicates
    ///   that the input string was partial and that the
    ///   invoking code should provide more code before
    ///   the code can be successfully compiled.
    ///
    ///   If you know that you will always get full expressions or
    ///   statements and do not care about partial input, you can use
    ///   the other Compile overload. 
    ///
    ///   On success, in addition to returning null, the
    ///   compiled parameter will be set to the delegate
    ///   that can be invoked to execute the code.
    ///
    /// </remarks>
    public string Compile (string input, out CompiledMethod compiled)
    {
      if (input == null || input.Length == 0){
        compiled = null;
        return null;
      }

      lock (evaluator_lock){
        if (!inited) {
          Init ();
          ParseStartupFiles ();
        } else {
          ctx.Report.Printer.Reset ();
        }

        bool partial_input;
        CSharpParser parser = ParseString (ParseMode.Silent, input, out partial_input);

        // Terse mode, try to provide the trailing semicolon automatically.
        if (parser == null && Terse && partial_input){
          bool ignore;

          // check if the source would compile with a block, if so, we should not
          // add the semicolon.
          var needs_block = ParseString (ParseMode.Silent, input + "{}", out ignore) != null;
          if (!needs_block)
            parser = ParseString (ParseMode.Silent, input + ";", out ignore);
        }
        if (parser == null){
          compiled = null;
          if (partial_input)
            return input;
          
          ParseString (ParseMode.ReportErrors, input, out partial_input);
          return null;
        }
        
        Class parser_result = parser.InteractiveResult;
        compiled = CompileBlock (parser_result, parser.undo, ctx.Report);
        return null;
      }
    }

    /// <summary>
    ///   Compiles the input string and returns a delegate that represents the compiled code.
    /// </summary>
    /// <remarks>
    ///
    ///   Compiles the input string as a C# expression or
    ///   statement, unlike the Evaluate method, the
    ///   resulting delegate can be invoked multiple times
    ///   without incurring in the compilation overhead.
    ///
    ///   This method can only deal with fully formed input
    ///   strings and does not provide a completion mechanism.
    ///   If you must deal with partial input (for example for
    ///   interactive use) use the other overload. 
    ///
    ///   On success, a delegate is returned that can be used
    ///   to invoke the method.
    ///
    /// </remarks>
    public CompiledMethod Compile (string input)
    {
      CompiledMethod compiled;

      // Ignore partial inputs
      if (Compile (input, out compiled) != null){
        // Error, the input was partial.
        return null;
      }

      // Either null (on error) or the compiled method.
      return compiled;
    }

    static MethodInfo listener_proxy_value;
    internal void EmitValueChangedCallback (EmitContext ec, string name, TypeSpec type, Location loc)
    {
      if (listener_id == null)
        listener_id = ListenerProxy.Register (ModificationListener);

      if (listener_proxy_value == null)
        listener_proxy_value = typeof (ListenerProxy).GetMethod ("ValueChanged");

#if STATIC
      throw new NotSupportedException ();
#else
      // object value, int row, int col, string name, int listenerId
      if (type.IsStructOrEnum)
        ec.Emit (OpCodes.Box, type);

      ec.EmitInt (loc.Row);
      ec.EmitInt (loc.Column);
      ec.Emit (OpCodes.Ldstr, name);
      ec.EmitInt (listener_id.Value);
      ec.Emit (OpCodes.Call, listener_proxy_value);
#endif
    }

    /// <summary>
    ///   Evaluates and expression or statement and returns any result values.
    /// </summary>
    /// <remarks>
    ///   Evaluates the input string as a C# expression or
    ///   statement.  If the input string is an expression
    ///   the result will be stored in the result variable
    ///   and the result_set variable will be set to true.
    ///
    ///   It is necessary to use the result/result_set
    ///   pair to identify when a result was set (for
    ///   example, execution of user-provided input can be
    ///   an expression, a statement or others, and
    ///   result_set would only be set if the input was an
    ///   expression.
    ///
    ///   If the return value of this function is null,
    ///   this indicates that the parsing was complete.
    ///   If the return value is a string, it indicates
    ///   that the input is partial and that the user
    ///   should provide an updated string.
    /// </remarks>
    public string Evaluate (string input, out object result, out bool result_set)
    {
      CompiledMethod compiled;

      result_set = false;
      result = null;

      input = Compile (input, out compiled);
      if (input != null)
        return input;
      
      if (compiled == null)
        return null;
        
      //
      // The code execution does not need to keep the compiler lock
      //
      object retval = typeof (QuitValue);

      try {
        invoke_thread = System.Threading.Thread.CurrentThread;
        invoking = true;
        compiled (ref retval);
      } catch (ThreadAbortException e){
        Thread.ResetAbort ();
        Console.WriteLine ("Interrupted!\n{0}", e);
      } finally {
        invoking = false;

        if (listener_id != null) {
          ListenerProxy.Unregister (listener_id.Value);
          listener_id = null;
        }
      }

      //
      // We use a reference to a compiler type, in this case
      // Driver as a flag to indicate that this was a statement
      //
      if (!ReferenceEquals (retval, typeof (QuitValue))) {
        result_set = true;
        result = retval; 
      }

      return null;
    }

    public string [] GetCompletions (string input, out string prefix)
    {
      prefix = "";
      if (input == null || input.Length == 0)
        return null;
      
      lock (evaluator_lock){
        if (!inited)
          Init ();
        
        bool partial_input;
        CSharpParser parser = ParseString (ParseMode.GetCompletions, input, out partial_input);
        if (parser == null){
          return null;
        }

        Class host = parser.InteractiveResult;

        var base_class_imported = importer.ImportType (base_class);
        var baseclass_list = new List<FullNamedExpression> (1) {
          new TypeExpression (base_class_imported, host.Location)
        };
        host.SetBaseTypes (baseclass_list);

#if NET_4_0
        var access = AssemblyBuilderAccess.RunAndCollect;
#else
        var access = AssemblyBuilderAccess.Run;
#endif
        var a = new AssemblyDefinitionDynamic (module, "completions");
        a.Create (AppDomain.CurrentDomain, access);
        module.SetDeclaringAssembly (a);

        // Need to setup MemberCache
        host.CreateContainer ();
        // Need to setup base type
        host.DefineContainer ();

        var method = host.Members[0] as Method;
        BlockContext bc = new BlockContext (method, method.Block, ctx.BuiltinTypes.Void);

        try {
          method.Block.Resolve (bc, method);
        } catch (CompletionResult cr) {
          prefix = cr.BaseText;
          return cr.Result;
        } 
      }
      return null;
    }

    /// <summary>
    ///   Executes the given expression or statement.
    /// </summary>
    /// <remarks>
    ///    Executes the provided statement, returns true
    ///    on success, false on parsing errors.  Exceptions
    ///    might be thrown by the called code.
    /// </remarks>
    public bool Run (string statement)
    {
      object result;
      bool result_set;

      return Evaluate (statement, out result, out result_set) == null;
    }

    /// <summary>
    ///   Evaluates and expression or statement and returns the result.
    /// </summary>
    /// <remarks>
    ///   Evaluates the input string as a C# expression or
    ///   statement and returns the value.   
    ///
    ///   This method will throw an exception if there is a syntax error,
    ///   of if the provided input is not an expression but a statement.
    /// </remarks>
    public object Evaluate (string input)
    {
      object result;
      bool result_set;
      
      string r = Evaluate (input, out result, out result_set);

      if (r != null)
        throw new ArgumentException ("Syntax error on input: partial input");
      
      if (result_set == false)
        throw new ArgumentException ("The expression failed to resolve");

      return result;
    }

    /// <summary>
    /// Experimental!
    /// </summary>
    public ValueModificationHandler ModificationListener { get; set; }

    enum InputKind {
      EOF,
      StatementOrExpression,
      CompilationUnit,
      Error
    }

    //
    // Deambiguates the input string to determine if we
    // want to process a statement or if we want to
    // process a compilation unit.
    //
    // This is done using a top-down predictive parser,
    // since the yacc/jay parser can not deambiguage this
    // without more than one lookahead token.   There are very
    // few ambiguities.
    //
    InputKind ToplevelOrStatement (SeekableStreamReader seekable)
    {
      Tokenizer tokenizer = new Tokenizer (seekable, source_file, new ParserSession (), ctx.Report);
      
      // Prefer contextual block keywords over identifiers
      tokenizer.parsing_block++;

      int t = tokenizer.token ();
      switch (t){
      case Token.EOF:
        return InputKind.EOF;
        
      // These are toplevels
      case Token.EXTERN:
      case Token.OPEN_BRACKET:
      case Token.ABSTRACT:
      case Token.CLASS:
      case Token.ENUM:
      case Token.INTERFACE:
      case Token.INTERNAL:
      case Token.NAMESPACE:
      case Token.PRIVATE:
      case Token.PROTECTED:
      case Token.PUBLIC:
      case Token.SEALED:
      case Token.STATIC:
      case Token.STRUCT:
        return InputKind.CompilationUnit;
        
      // Definitely expression
      case Token.FIXED:
      case Token.BOOL:
      case Token.BYTE:
      case Token.CHAR:
      case Token.DECIMAL:
      case Token.DOUBLE:
      case Token.FLOAT:
      case Token.INT:
      case Token.LONG:
      case Token.NEW:
      case Token.OBJECT:
      case Token.SBYTE:
      case Token.SHORT:
      case Token.STRING:
      case Token.UINT:
      case Token.ULONG:
        return InputKind.StatementOrExpression;

      // These need deambiguation help
      case Token.USING:
        t = tokenizer.token ();
        if (t == Token.EOF)
          return InputKind.EOF;

        if (t == Token.IDENTIFIER)
          return InputKind.CompilationUnit;
        return InputKind.StatementOrExpression;


      // Distinguish between:
      //    delegate opt_anonymous_method_signature block
      //    delegate type 
      case Token.DELEGATE:
        t = tokenizer.token ();
        if (t == Token.EOF)
          return InputKind.EOF;
        if (t == Token.OPEN_PARENS || t == Token.OPEN_BRACE)
          return InputKind.StatementOrExpression;
        return InputKind.CompilationUnit;

      // Distinguih between:
      //    unsafe block
      //    unsafe as modifier of a type declaration
      case Token.UNSAFE:
        t = tokenizer.token ();
        if (t == Token.EOF)
          return InputKind.EOF;
        if (t == Token.OPEN_PARENS)
          return InputKind.StatementOrExpression;
        return InputKind.CompilationUnit;
        
            // These are errors: we list explicitly what we had
      // from the grammar, ERROR and then everything else

      case Token.READONLY:
      case Token.OVERRIDE:
      case Token.ERROR:
        return InputKind.Error;

      // This catches everything else allowed by
      // expressions.  We could add one-by-one use cases
      // if needed.
      default:
        return InputKind.StatementOrExpression;
      }
    }
    
    //
    // Parses the string @input and returns a CSharpParser if succeeful.
    //
    // if @silent is set to true then no errors are
    // reported to the user.  This is used to do various calls to the
    // parser and check if the expression is parsable.
    //
    // @partial_input: if @silent is true, then it returns whether the
    // parsed expression was partial, and more data is needed
    //
    CSharpParser ParseString (ParseMode mode, string input, out bool partial_input)
    {
      partial_input = false;
      Reset ();

      var enc = ctx.Settings.Encoding;
      var s = new MemoryStream (enc.GetBytes (input));
      SeekableStreamReader seekable = new SeekableStreamReader (s, enc);

      InputKind kind = ToplevelOrStatement (seekable);
      if (kind == InputKind.Error){
        if (mode == ParseMode.ReportErrors)
          ctx.Report.Error (-25, "Detection Parsing Error");
        partial_input = false;
        return null;
      }

      if (kind == InputKind.EOF){
        if (mode == ParseMode.ReportErrors)
          Console.Error.WriteLine ("Internal error: EOF condition should have been detected in a previous call with silent=true");
        partial_input = true;
        return null;
        
      }
      seekable.Position = 0;

      source_file.DeclarationFound = false;
      CSharpParser parser = new CSharpParser (seekable, source_file, new ParserSession ());

      if (kind == InputKind.StatementOrExpression){
        parser.Lexer.putback_char = Tokenizer.EvalStatementParserCharacter;
        parser.Lexer.parsing_block++;
        ctx.Settings.StatementMode = true;
      } else {
        parser.Lexer.putback_char = Tokenizer.EvalCompilationUnitParserCharacter;
        ctx.Settings.StatementMode = false;
      }

      if (mode == ParseMode.GetCompletions)
        parser.Lexer.CompleteOnEOF = true;

      ReportPrinter old_printer = null;
      if ((mode == ParseMode.Silent || mode == ParseMode.GetCompletions))
        old_printer = ctx.Report.SetPrinter (new StreamReportPrinter (TextWriter.Null));

      try {
        parser.parse ();
      } finally {
        if (ctx.Report.Errors != 0){
          if (mode != ParseMode.ReportErrors  && parser.UnexpectedEOF)
            partial_input = true;

          if (parser.undo != null)
            parser.undo.ExecuteUndo ();

          parser = null;
        }

        if (old_printer != null)
          ctx.Report.SetPrinter (old_printer);
      }
      return parser;
    }

    CompiledMethod CompileBlock (Class host, Undo undo, Report Report)
    {
#if STATIC
      throw new NotSupportedException ();
#else
      string current_debug_name = "eval-" + count + ".dll";
      ++count;

      AssemblyDefinitionDynamic assembly;
      AssemblyBuilderAccess access;

      if (Environment.GetEnvironmentVariable ("SAVE") != null) {
        access = AssemblyBuilderAccess.RunAndSave;
        assembly = new AssemblyDefinitionDynamic (module, current_debug_name, current_debug_name);
        assembly.Importer = importer;
      } else {
#if NET_4_0
        access = AssemblyBuilderAccess.RunAndCollect;
#else
        access = AssemblyBuilderAccess.Run;
#endif
        assembly = new AssemblyDefinitionDynamic (module, current_debug_name);
      }

      assembly.Create (AppDomain.CurrentDomain, access);

      Method expression_method;
      if (host != null) {
        var base_class_imported = importer.ImportType (base_class);
        var baseclass_list = new List<FullNamedExpression> (1) {
          new TypeExpression (base_class_imported, host.Location)
        };

        host.SetBaseTypes (baseclass_list);

        expression_method = (Method) host.Members[0];

        if ((expression_method.ModFlags & Modifiers.ASYNC) != 0) {
          //
          // Host method is async. When WaitOnTask is set we wrap it with wait
          //
          // void AsyncWait (ref object $retval) {
          //  $retval = Host();
          //  ((Task)$retval).Wait();  // When WaitOnTask is set
          // }
          //
          var p = new ParametersCompiled (
            new Parameter (new TypeExpression (module.Compiler.BuiltinTypes.Object, Location.Null), "$retval", Parameter.Modifier.REF, null, Location.Null)
          );

          var method = new Method(host, new TypeExpression(module.Compiler.BuiltinTypes.Void, Location.Null),
            Modifiers.PUBLIC | Modifiers.STATIC, new MemberName("AsyncWait"), p, null);

          method.Block = new ToplevelBlock(method.Compiler, p, Location.Null);
          method.Block.AddStatement(new StatementExpression (new SimpleAssign(
            new SimpleName(p [0].Name, Location.Null),
            new Invocation(new SimpleName(expression_method.MemberName.Name, Location.Null), new Arguments(0)),
            Location.Null), Location.Null));

          if (WaitOnTask) {
            var task = new Cast (expression_method.TypeExpression, new SimpleName (p [0].Name, Location.Null), Location.Null);

            method.Block.AddStatement (new StatementExpression (new Invocation (
                new MemberAccess (task, "Wait", Location.Null),
              new Arguments (0)), Location.Null));
          }

          host.AddMember(method);

          expression_method = method;
        }

        host.CreateContainer();
        host.DefineContainer();
        host.Define();

      } else {
        expression_method = null;
      }

      module.CreateContainer ();

      // Disable module and source file re-definition checks
      module.EnableRedefinition ();
      source_file.EnableRedefinition ();

      module.Define ();

      if (Report.Errors != 0){
        if (undo != null)
          undo.ExecuteUndo ();

        return null;
      }

      if (host != null){
        host.PrepareEmit ();
        host.EmitContainer ();
      }
      
      module.EmitContainer ();

      if (Report.Errors != 0){
        if (undo != null)
          undo.ExecuteUndo ();
        return null;
      }

      module.CloseContainer ();
      if (host != null)
        host.CloseContainer ();

      if (access == AssemblyBuilderAccess.RunAndSave)
        assembly.Save ();

      if (host == null)
        return null;
      
      //
      // Unlike Mono, .NET requires that the MethodInfo is fetched, it cant
      // work from MethodBuilders.   Retarded, I know.
      //
      var tt = assembly.Builder.GetType (host.TypeBuilder.Name);
      var mi = tt.GetMethod (expression_method.MemberName.Name);

      //
      // We need to then go from FieldBuilder to FieldInfo
      // or reflection gets confused (it basically gets confused, and variables override each
      // other).
      //
      foreach (var member in host.Members) {
        var field = member as Field;
        if (field == null)
          continue;

        var fi = tt.GetField (field.Name);

        Tuple<FieldSpec, FieldInfo> old;

        // If a previous value was set, nullify it, so that we do
        // not leak memory
        if (fields.TryGetValue (field.Name, out old)) {
          if (old.Item1.MemberType.IsStruct) {
            //
            // TODO: Clear fields for structs
            //
          } else {
            try {
              old.Item2.SetValue (null, null);
            } catch {
            }
          }
        }

        fields[field.Name] = Tuple.Create (field.Spec, fi);
      }
      
      return (CompiledMethod) System.Delegate.CreateDelegate (typeof (CompiledMethod), mi);
#endif
    }

    /// <summary>
    ///   A sentinel value used to indicate that no value was
    ///   was set by the compiled function.   This is used to
    ///   differentiate between a function not returning a
    ///   value and null.
    /// </summary>
    internal static class QuitValue { }

    internal Tuple<FieldSpec, FieldInfo> LookupField (string name)
    {
      Tuple<FieldSpec, FieldInfo> fi;
      fields.TryGetValue (name, out fi);
      return fi;
    }

    static string Quote (string s)
    {
      if (s.IndexOf ('"') != -1)
        s = s.Replace ("\"", "\\\"");
      
      return "\"" + s + "\"";
    }

    public string GetUsing ()
    {
      StringBuilder sb = new StringBuilder ();
      // TODO:
      //foreach (object x in ns.using_alias_list)
      //    sb.AppendFormat ("using {0};\n", x);

      foreach (var ue in source_file.Usings) {
        sb.AppendFormat ("using {0};", ue.ToString ());
        sb.Append (Environment.NewLine);
      }

      return sb.ToString ();
    }

    internal List<string> GetUsingList ()
    {
      var res = new List<string> ();

      foreach (var ue in source_file.Usings) {
        if (ue.Alias != null || ue.ResolvedExpression == null)
          continue;

        res.Add (ue.NamespaceExpression.Name);
      }

      return res;
    }
    
    internal string [] GetVarNames ()
    {
      lock (evaluator_lock){
        return new List<string> (fields.Keys).ToArray ();
      }
    }
    
    public string GetVars ()
    {
      lock (evaluator_lock){
        StringBuilder sb = new StringBuilder ();
        
        foreach (var de in fields){
          var fi = LookupField (de.Key);
          object value;
          try {
            value = fi.Item2.GetValue (null);
            if (value is string)
              value = Quote ((string)value);
          } catch {
            value = "<error reading value>";
          }

          sb.AppendFormat ("{0} {1} = {2}", fi.Item1.MemberType.GetSignatureForError (), de.Key, value);
          sb.AppendLine ();
        }
        
        return sb.ToString ();
      }
    }

    /// <summary>
    ///    Loads the given assembly and exposes the API to the user.
    /// </summary>
    public void LoadAssembly (string file)
    {
      var loader = new DynamicLoader (importer, ctx);
      var assembly = loader.LoadAssemblyFile (file, false);
      if (assembly == null)
        return;

      lock (evaluator_lock){
        importer.ImportAssembly (assembly, module.GlobalRootNamespace);
      }
    }

    /// <summary>
    ///    Exposes the API of the given assembly to the Evaluator
    /// </summary>
    public void ReferenceAssembly (Assembly a)
    {
      lock (evaluator_lock){
        importer.ImportAssembly (a, module.GlobalRootNamespace);
      }
    }
  }

  
  /// <summary>
  ///   A delegate that can be used to invoke the
  ///   compiled expression or statement.
  /// </summary>
  /// <remarks>
  ///   Since the Compile methods will compile
  ///   statements and expressions into the same
  ///   delegate, you can tell if a value was returned
  ///   by checking whether the returned value is of type
  ///   NoValueSet.   
  /// </remarks>
  
  public delegate void CompiledMethod (ref object retvalue);

  /// <summary>
  ///   The default base class for every interaction line
  /// </summary>
  /// <remarks>
  ///   The expressions and statements behave as if they were
  ///   a static method of this class.   The InteractiveBase class
  ///   contains a number of useful methods, but can be overwritten
  ///   by setting the InteractiveBaseType property in the Evaluator
  /// </remarks>
  public class InteractiveBase {
    /// <summary>
    ///   Determines where the standard output of methods in this class will go. 
    /// </summary>
    public static TextWriter Output = Console.Out;

    /// <summary>
    ///   Determines where the standard error of methods in this class will go. 
    /// </summary>
    public static TextWriter Error = Console.Error;

    /// <summary>
    ///   The primary prompt used for interactive use.
    /// </summary>
    public static string Prompt             = "csharp> ";

    /// <summary>
    ///   The secondary prompt used for interactive use (used when
    ///   an expression is incomplete).
    /// </summary>
    public static string ContinuationPrompt = "      > ";

    /// <summary>
    ///   Used to signal that the user has invoked the  `quit' statement.
    /// </summary>
    public static bool QuitRequested;

    public static Evaluator Evaluator;
    
    /// <summary>
    ///   Shows all the variables defined so far.
    /// </summary>
    static public void ShowVars ()
    {
      Output.Write (Evaluator.GetVars ());
      Output.Flush ();
    }

    /// <summary>
    ///   Displays the using statements in effect at this point. 
    /// </summary>
    static public void ShowUsing ()
    {
      Output.Write (Evaluator.GetUsing ());
      Output.Flush ();
    }
  
    /// <summary>
    ///   Times the execution of the given delegate
    /// </summary>
    static public TimeSpan Time (Action a)
    {
      DateTime start = DateTime.Now;
      a ();
      return DateTime.Now - start;
    }
    
    /// <summary>
    ///   Loads the assemblies from a package
    /// </summary>
    /// <remarks>
    ///   Loads the assemblies from a package.   This is equivalent
    ///   to passing the -pkg: command line flag to the C# compiler
    ///   on the command line. 
    /// </remarks>
    static public void LoadPackage (string pkg)
    {
      if (pkg == null){
        Error.WriteLine ("Invalid package specified");
        return;
      }

      string pkgout = Driver.GetPackageFlags (pkg, null);

      string [] xargs = pkgout.Trim (new Char [] {' ', '\n', '\r', '\t'}).
        Split (new Char [] { ' ', '\t'});

      foreach (string s in xargs){
        if (s.StartsWith ("-r:") || s.StartsWith ("/r:") || s.StartsWith ("/reference:")){
          string lib = s.Substring (s.IndexOf (':')+1);

          Evaluator.LoadAssembly (lib);
          continue;
        }
      }
    }

    /// <summary>
    ///   Loads the assembly
    /// </summary>
    /// <remarks>
    ///   Loads the specified assembly and makes its types
    ///   available to the evaluator.  This is equivalent
    ///   to passing the -pkg: command line flag to the C#
    ///   compiler on the command line.
    /// </remarks>
    static public void LoadAssembly (string assembly)
    {
      Evaluator.LoadAssembly (assembly);
    }

    static public void print (object obj)
    {
      Output.WriteLine (obj);
    }

    static public void print (string fmt, params object [] args)
    {
      Output.WriteLine (fmt, args);
    }
    
    /// <summary>
    ///   Returns a list of available static methods. 
    /// </summary>
    static public string help {
      get {
        return "Static methods:\n" +
          "  Describe (object);       - Describes the object's type\n" +
          "  LoadPackage (package);   - Loads the given Package (like -pkg:FILE)\n" +
          "  LoadAssembly (assembly); - Loads the given assembly (like -r:ASSEMBLY)\n" +
          "  ShowVars ();             - Shows defined local variables.\n" +
          "  ShowUsing ();            - Show active using declarations.\n" +
          "  Prompt                   - The prompt used by the C# shell\n" +
          "  ContinuationPrompt       - The prompt for partial input\n" +
          "  Time (() => { });        - Times the specified code\n" +
          "  print (obj);             - Shorthand for Console.WriteLine\n" +
          "  quit;                    - You'll never believe it - this quits the repl!\n" +
          "  help;                    - This help text\n";
      }
    }

    /// <summary>
    ///   Indicates to the read-eval-print-loop that the interaction should be finished. 
    /// </summary>
    static public object quit {
      get {
        QuitRequested = true;

        // To avoid print null at the exit
        return typeof (Evaluator.QuitValue);
      }
    }

    /// <summary>
    ///   Same as quit - useful in script scenerios
    /// </summary>
    static public void Quit () {
      QuitRequested = true;
    }

#if !NET_2_1
    /// <summary>
    ///   Describes an object or a type.
    /// </summary>
    /// <remarks>
    ///   This method will show a textual representation
    ///   of the object's type.  If the object is a
    ///   System.Type it renders the type directly,
    ///   otherwise it renders the type returned by
    ///   invoking GetType on the object.
    /// </remarks>
    static public string Describe (object x)
    {
      if (x == null)
        return "<null>";

      var type = x as Type ?? x.GetType ();

      StringWriter sw = new StringWriter ();
      new Outline (type, sw, true, false, false).OutlineType ();
      return sw.ToString ();
    }
#endif
  }

  class InteractiveMethod : Method
  {
    public InteractiveMethod(TypeDefinition parent, FullNamedExpression returnType, Modifiers mod, ParametersCompiled parameters)
      : base(parent, returnType, mod, new MemberName("Host"), parameters, null)
    {
    }

    public void ChangeToAsync ()
    {
      ModFlags |= Modifiers.ASYNC;
      ModFlags &= ~Modifiers.UNSAFE;
      type_expr = new TypeExpression(Module.PredefinedTypes.Task.TypeSpec, Location);
      parameters = ParametersCompiled.EmptyReadOnlyParameters;
    }

    public override string GetSignatureForError()
    {
      return "InteractiveHost";
    }
  }

  class HoistedEvaluatorVariable : HoistedVariable
  {
    public HoistedEvaluatorVariable (Field field)
      : base (null, field)
    {
    }

    protected override FieldExpr GetFieldExpression (EmitContext ec)
    {
      return new FieldExpr (field, field.Location);
    }
  }

  /// <summary>
  ///    A class used to assign values if the source expression is not void
  ///
  ///    Used by the interactive shell to allow it to call this code to set
  ///    the return value for an invocation.
  /// </summary>
  class OptionalAssign : SimpleAssign {
    public OptionalAssign (Expression s, Location loc)
      : base (null, s, loc)
    {
    }

    public override Location StartLocation {
      get {
        return Location.Null;
      }
    }

    protected override Expression DoResolve (ResolveContext ec)
    {
      Expression clone = source.Clone (new CloneContext ());

      clone = clone.Resolve (ec);
      if (clone == null)
        return null;

      //
      // A useful feature for the REPL: if we can resolve the expression
      // as a type, Describe the type;
      //
      if (ec.Module.Evaluator.DescribeTypeExpressions && !(ec.CurrentAnonymousMethod is AsyncInitializer)) {
        var old_printer = ec.Report.SetPrinter (new SessionReportPrinter ());
        Expression tclone;
        try {
          // Note: clone context cannot be shared otherwise block mapping would leak
          tclone = source.Clone (new CloneContext ());
          tclone = tclone.Resolve (ec, ResolveFlags.Type);
          if (ec.Report.Errors > 0)
            tclone = null;
        } finally {
          ec.Report.SetPrinter (old_printer);
        }

        if (tclone is TypeExpr) {
          Arguments args = new Arguments (1);
          args.Add (new Argument (new TypeOf ((TypeExpr) clone, Location)));
          return new Invocation (new SimpleName ("Describe", Location), args).Resolve (ec);
        }
      }

      // This means its really a statement.
      if (clone.Type.Kind == MemberKind.Void || clone is DynamicInvocation || clone is Assign) {
        return clone;
      }

      source = clone;

      var host = (Method) ec.MemberContext.CurrentMemberDefinition;

      if (host.ParameterInfo.IsEmpty) {
        eclass = ExprClass.Value;
        type = InternalType.FakeInternalType;
        return this;
      }

      target = new SimpleName (host.ParameterInfo[0].Name, Location);

      return base.DoResolve (ec);
    }

    public override void EmitStatement(EmitContext ec)
    {
      if (target == null) {
        source.Emit (ec);
        return;
      }

      base.EmitStatement(ec);
    }
  }

  public class Undo
  {
    List<Action> undo_actions;

    public void AddTypeContainer (TypeContainer current_container, TypeDefinition tc)
    {
      if (current_container == tc){
        Console.Error.WriteLine ("Internal error: inserting container into itself");
        return;
      }

      if (undo_actions == null)
        undo_actions = new List<Action> ();

      if (current_container.Containers != null)
      {
        var existing = current_container.Containers.FirstOrDefault (l => l.Basename == tc.Basename);
        if (existing != null) {
          current_container.RemoveContainer (existing);
          undo_actions.Add (() => current_container.AddTypeContainer (existing));
        }
      }

      undo_actions.Add (() => current_container.RemoveContainer (tc));
    }

    public void ExecuteUndo ()
    {
      if (undo_actions == null)
        return;

      foreach (var p in undo_actions){
        p ();
      }

      undo_actions = null;
    }
  }

  static class ListenerProxy
  {
    static readonly Dictionary<int, ValueModificationHandler> listeners = new Dictionary<int, ValueModificationHandler> ();

    static int counter;

    public static int Register (ValueModificationHandler listener)
    {
      lock (listeners) {
        var id = counter++;
        listeners.Add (id, listener);
        return id;
      }
    }

    public static void Unregister (int listenerId)
    {
      lock (listeners) {
        listeners.Remove (listenerId);
      }
    }

    public static void ValueChanged (object value, int row, int col, string name, int listenerId)
    {
      ValueModificationHandler action;
      lock (listeners) {
        if (!listeners.TryGetValue (listenerId, out action))
          return;
      }

      action (name, row, col, value);
    }
  }
}