mcs/mcs/eval.cs

   1 //
   2 // eval.cs: Evaluation and Hosting API for the C# compiler
   3 //
   4 // Authors:
   5 //   Miguel de Icaza (miguel@gnome.org)
   6 //
   7 // Dual licensed under the terms of the MIT X11 or GNU GPL
   8 //
   9 // Copyright 2001, 2002, 2003 Ximian, Inc (http://www.ximian.com)
  10 // Copyright 2004, 2005, 2006, 2007, 2008 Novell, Inc
  11 //
  12 using System;
  13 using System.Threading;
  14 using System.Collections;
  15 using System.Reflection;
  16 using System.Reflection.Emit;
  17 using System.IO;
  18 using System.Globalization;
  19 using System.Text;
  20
  21 namespace Mono.CSharp {
  22
  23         /// <summary>
  24         ///   Evaluator: provides an API to evaluate C# statements and
  25         ///   expressions dynamically.
  26         /// </summary>
  27         /// <remarks>
  28         ///   This class exposes static methods to evaluate expressions in the
  29         ///   current program.
  30         ///
  31         ///   To initialize the evaluator with a number of compiler
  32         ///   options call the Init(string[]args) method with a set of
  33         ///   command line options that the compiler recognizes.
  34         ///
  35         ///   To interrupt execution of a statement, you can invoke the
  36         ///   Evaluator.Interrupt method.
  37         /// </remarks>
  38         public class Evaluator {
  39                 static string current_debug_name;
  40                 static int count;
  41                 static Thread invoke_thread;
  42
  43                 static ArrayList using_alias_list = new ArrayList ();
  44                 static ArrayList using_list = new ArrayList ();
  45                 static Hashtable fields = new Hashtable ();
  46
  47                 static Type   interactive_base_class = typeof (InteractiveBase);
  48                 static Driver driver;
  49                 static bool inited;
  50
  51                 /// <summary>
  52                 ///   Optional initialization for the Evaluator.
  53                 /// </summary>
  54                 /// <remarks>
  55                 ///  Initializes the Evaluator with the command line options
  56                 ///  that would be processed by the command line compiler.  Only
  57                 ///  the first call to Init will work, any future invocations are
  58                 ///  ignored.
  59                 ///
  60                 ///  You can safely avoid calling this method if your application
  61                 ///  does not need any of the features exposed by the command line
  62                 ///  interface.
  63                 /// </remarks>
  64                 public static void Init (string [] args)
  65                 {
  66                         if (inited)
  67                                 return;
  68
  69                         RootContext.Version = LanguageVersion.Default;
  70                         driver = Driver.Create (args, false);
  71                         if (driver == null)
  72                                 throw new Exception ("Failed to create compiler driver with the given arguments");
  73
  74                         driver.ProcessDefaultConfig ();
  75                         CompilerCallableEntryPoint.Reset ();
  76                         Driver.LoadReferences ();
  77                         RootContext.EvalMode = true;
  78                         inited = true;
  79                 }
  80
  81                 static void Init ()
  82                 {
  83                         Init (new string [0]);
  84                 }
  85
  86                 static void Reset ()
  87                 {
  88                         CompilerCallableEntryPoint.PartialReset ();
  89
  90                         //
  91                         // PartialReset should not reset the core types, this is very redundant.
  92                         //
  93                         if (!TypeManager.InitCoreTypes ())
  94                                 throw new Exception ("Failed to InitCoreTypes");
  95                         TypeManager.InitOptionalCoreTypes ();
  96
  97                         Location.AddFile ("<interactive>");
  98                         Location.Initialize ();
  99
 100                         current_debug_name = "interactive" + (count++) + ".dll";
 101                         if (Environment.GetEnvironmentVariable ("SAVE") != null){
 102                                 CodeGen.Init (current_debug_name, current_debug_name, false);
 103                         } else
 104                                 CodeGen.InitDynamic (current_debug_name);
 105                 }
 106
 107                 /// <summary>
 108                 ///   The base class for the classes that host the user generated code
 109                 /// </summary>
 110                 /// <remarks>
 111                 ///
 112                 ///   This is the base class that will host the code
 113                 ///   executed by the Evaluator.  By default
 114                 ///   this is the Mono.CSharp.InteractiveBase class
 115                 ///   which is useful for interactive use.
 116                 ///
 117                 ///   By changing this property you can control the
 118                 ///   base class and the static members that are
 119                 ///   available to your evaluated code.
 120                 /// </remarks>
 121                 static public Type InteractiveBaseClass {
 122                         get {
 123                                 return interactive_base_class;
 124                         }
 125
 126                         set {
 127                                 if (value == null)
 128                                         throw new ArgumentNullException ();
 129
 130                                 interactive_base_class = value;
 131                         }
 132                 }
 133
 134                 /// <summary>
 135                 ///   Interrupts the evaluation of an expression.
 136                 /// </summary>
 137                 /// <remarks>
 138                 ///   Use this method to interrupt long-running invocations.
 139                 /// </remarks>
 140                 public static void Interrupt ()
 141                 {
 142                         if (!inited || !invoking)
 143                                 return;
 144
 145                         if (invoke_thread != null)
 146                                 invoke_thread.Abort ();
 147                 }
 148
 149                 //
 150                 // Todo: Should we handle errors, or expect the calling code to setup
 151                 // the recording themselves?
 152                 //
 153
 154                 /// <summary>
 155                 ///   Evaluates and expression or statement and returns any result values.
 156                 /// </summary>
 157                 /// <remarks>
 158                 ///   Evaluates the input string as a C# expression or
 159                 ///   statement.  If the input string is an expression
 160                 ///   the result will be stored in the result variable
 161                 ///   and the result_set variable will be set to true.
 162                 ///
 163                 ///   It is necessary to use the result/result_set
 164                 ///   pair to identify when a result was set (for
 165                 ///   example, execution of user-provided input can be
 166                 ///   an expression, a statement or others, and
 167                 ///   result_set would only be set if the input was an
 168                 ///   expression.
 169                 ///
 170                 ///   If the return value of this function is null,
 171                 ///   this indicates that the parsing was complete.
 172                 ///   If the return value is a string, it indicates
 173                 ///   that the input is partial and that the user
 174                 ///   should provide an updated string.
 175                 /// </remarks>
 176                 public static string Evaluate (string input, out object result, out bool result_set)
 177                 {
 178                         result_set = false;
 179                         result = null;
 180
 181                         if (input == null || input.Length == 0)
 182                                 return null;
 183
 184                         if (!inited)
 185                                 Init ();
 186
 187                         bool partial_input;
 188                         CSharpParser parser = ParseString (true, input, out partial_input);
 189                         if (parser == null){
 190                                 if (partial_input)
 191                                         return input;
 192
 193                                 ParseString (false, input, out partial_input);
 194                                 return null;
 195                         }
 196
 197                         object parser_result = parser.InteractiveResult;
 198
 199                         if (!(parser_result is Class))
 200                                 parser.CurrentNamespace.Extract (using_alias_list, using_list);
 201
 202                         result = ExecuteBlock (parser_result as Class, parser.undo);
 203                         //
 204                         // We use a reference to a compiler type, in this case
 205                         // Driver as a flag to indicate that this was a statement
 206                         //
 207                         if (result != typeof (NoValueSet))
 208                                 result_set = true;
 209
 210                         return null;
 211                 }
 212
 213                 /// <summary>
 214                 ///   Executes the given expression or statement.
 215                 /// </summary>
 216                 /// <remarks>
 217                 ///    Executes the provided statement, returns true
 218                 ///    on success, false on parsing errors.  Exceptions
 219                 ///    might be thrown by the called code.
 220                 /// </remarks>
 221                 public static bool Run (string statement)
 222                 {
 223                         if (!inited)
 224                                 Init ();
 225
 226                         object result;
 227                         bool result_set;
 228
 229                         bool ok = Evaluate (statement, out result, out result_set) == null;
 230
 231                         return ok;
 232                 }
 233
 234                 /// <summary>
 235                 ///   Evaluates and expression or statement and returns the result.
 236                 /// </summary>
 237                 /// <remarks>
 238                 ///   Evaluates the input string as a C# expression or
 239                 ///   statement and returns the value.
 240                 ///
 241                 ///   This method will throw an exception if there is a syntax error,
 242                 ///   of if the provided input is not an expression but a statement.
 243                 /// </remarks>
 244                 public static object Evaluate (string input)
 245                 {
 246                         object result;
 247                         bool result_set;
 248
 249                         string r = Evaluate (input, out result, out result_set);
 250
 251                         if (r != null)
 252                                 throw new ArgumentException ("Syntax error on input: partial input");
 253
 254                         if (result_set == false)
 255                                 throw new ArgumentException ("The expression did not set a result");
 256
 257                         return result;
 258                 }
 259
 260                 enum InputKind {
 261                         EOF,
 262                         StatementOrExpression,
 263                         CompilationUnit,
 264                         Error
 265                 }
 266
 267                 //
 268                 // Deambiguates the input string to determine if we
 269                 // want to process a statement or if we want to
 270                 // process a compilation unit.
 271                 //
 272                 // This is done using a top-down predictive parser,
 273                 // since the yacc/jay parser can not deambiguage this
 274                 // without more than one lookahead token.   There are very
 275                 // few ambiguities.
 276                 //
 277                 static InputKind ToplevelOrStatement (SeekableStreamReader seekable)
 278                 {
 279                         Tokenizer tokenizer = new Tokenizer (seekable, Location.SourceFiles [0]);
 280
 281                         int t = tokenizer.token ();
 282                         switch (t){
 283                         case Token.EOF:
 284                                 return InputKind.EOF;
 285
 286                         // These are toplevels
 287                         case Token.EXTERN:
 288                         case Token.OPEN_BRACKET:
 289                         case Token.ABSTRACT:
 290                         case Token.CLASS:
 291                         case Token.ENUM:
 292                         case Token.INTERFACE:
 293                         case Token.INTERNAL:
 294                         case Token.NAMESPACE:
 295                         case Token.PRIVATE:
 296                         case Token.PROTECTED:
 297                         case Token.PUBLIC:
 298                         case Token.SEALED:
 299                         case Token.STATIC:
 300                         case Token.STRUCT:
 301                                 return InputKind.CompilationUnit;
 302
 303                         // Definitely expression
 304                         case Token.FIXED:
 305                         case Token.BOOL:
 306                         case Token.BYTE:
 307                         case Token.CHAR:
 308                         case Token.DECIMAL:
 309                         case Token.DOUBLE:
 310                         case Token.FLOAT:
 311                         case Token.INT:
 312                         case Token.LONG:
 313                         case Token.NEW:
 314                         case Token.OBJECT:
 315                         case Token.SBYTE:
 316                         case Token.SHORT:
 317                         case Token.STRING:
 318                         case Token.UINT:
 319                         case Token.ULONG:
 320                                 return InputKind.StatementOrExpression;
 321
 322                         // These need deambiguation help
 323                         case Token.USING:
 324                                 t = tokenizer.token ();
 325                                 if (t == Token.EOF)
 326                                         return InputKind.EOF;
 327
 328                                 if (t == Token.IDENTIFIER)
 329                                         return InputKind.CompilationUnit;
 330                                 return InputKind.StatementOrExpression;
 331
 332
 333                         // Distinguish between:
 334                         //    delegate opt_anonymous_method_signature block
 335                         //    delegate type
 336                         case Token.DELEGATE:
 337                                 t = tokenizer.token ();
 338                                 if (t == Token.EOF)
 339                                         return InputKind.EOF;
 340                                 if (t == Token.OPEN_PARENS || t == Token.OPEN_BRACE)
 341                                         return InputKind.StatementOrExpression;
 342                                 return InputKind.CompilationUnit;
 343
 344                         // Distinguih between:
 345                         //    unsafe block
 346                         //    unsafe as modifier of a type declaration
 347                         case Token.UNSAFE:
 348                                 t = tokenizer.token ();
 349                                 if (t == Token.EOF)
 350                                         return InputKind.EOF;
 351                                 if (t == Token.OPEN_PARENS)
 352                                         return InputKind.StatementOrExpression;
 353                                 return InputKind.CompilationUnit;
 354
 355                         // These are errors: we list explicitly what we had
 356                         // from the grammar, ERROR and then everything else
 357
 358                         case Token.READONLY:
 359                         case Token.OVERRIDE:
 360                         case Token.ERROR:
 361                                 return InputKind.Error;
 362
 363                         // This catches everything else allowed by
 364                         // expressions.  We could add one-by-one use cases
 365                         // if needed.
 366                         default:
 367                                 return InputKind.StatementOrExpression;
 368                         }
 369                 }
 370
 371                 //
 372                 // Parses the string @input and returns a CSharpParser if succeeful.
 373                 //
 374                 // if @silent is set to true then no errors are
 375                 // reported to the user.  This is used to do various calls to the
 376                 // parser and check if the expression is parsable.
 377                 //
 378                 // @partial_input: if @silent is true, then it returns whether the
 379                 // parsed expression was partial, and more data is needed
 380                 //
 381                 static CSharpParser ParseString (bool silent, string input, out bool partial_input)
 382                 {
 383                         partial_input = false;
 384                         Reset ();
 385                         queued_fields.Clear ();
 386
 387                         Stream s = new MemoryStream (Encoding.Default.GetBytes (input));
 388                         SeekableStreamReader seekable = new SeekableStreamReader (s, Encoding.Default);
 389
 390                         InputKind kind = ToplevelOrStatement (seekable);
 391                         if (kind == InputKind.Error){
 392                                 if (!silent)
 393                                         Report.Error (-25, "Detection Parsing Error");
 394                                 partial_input = false;
 395                                 return null;
 396                         }
 397
 398                         if (kind == InputKind.EOF){
 399                                 if (silent == false)
 400                                         Console.Error.WriteLine ("Internal error: EOF condition should have been detected in a previous call with silent=true");
 401                                 partial_input = true;
 402                                 return null;
 403
 404                         }
 405                         seekable.Position = 0;
 406
 407                         CSharpParser parser = new CSharpParser (seekable, Location.SourceFiles [0]);
 408                         parser.ErrorOutput = Report.Stderr;
 409
 410                         if (kind == InputKind.StatementOrExpression){
 411                                 parser.Lexer.putback_char = Tokenizer.EvalStatementParserCharacter;
 412                                 RootContext.StatementMode = true;
 413                         } else {
 414                                 //
 415                                 // Do not activate EvalCompilationUnitParserCharacter until
 416                                 // I have figured out all the limitations to invoke methods
 417                                 // in the generated classes.  See repl.txt
 418                                 //
 419                                 parser.Lexer.putback_char = Tokenizer.EvalUsingDeclarationsParserCharacter;
 420                                 //parser.Lexer.putback_char = Tokenizer.EvalCompilationUnitParserCharacter;
 421                                 RootContext.StatementMode = false;
 422                         }
 423
 424                         if (silent)
 425                                 Report.DisableReporting ();
 426                         try {
 427                                 parser.parse ();
 428                         } finally {
 429                                 if (Report.Errors != 0){
 430                                         if (silent && parser.UnexpectedEOF)
 431                                                 partial_input = true;
 432
 433                                         parser.undo.ExecuteUndo ();
 434                                         parser = null;
 435                                 }
 436
 437                                 if (silent)
 438                                         Report.EnableReporting ();
 439                         }
 440                         return parser;
 441                 }
 442
 443                 delegate void HostSignature (ref object retvalue);
 444
 445                 //
 446                 // Queue all the fields that we use, as we need to then go from FieldBuilder to FieldInfo
 447                 // or reflection gets confused (it basically gets confused, and variables override each
 448                 // other).
 449                 //
 450                 static ArrayList queued_fields = new ArrayList ();
 451
 452                 //static ArrayList types = new ArrayList ();
 453
 454                 static volatile bool invoking;
 455
 456                 static object ExecuteBlock (Class host, Undo undo)
 457                 {
 458                         RootContext.ResolveTree ();
 459                         if (Report.Errors != 0){
 460                                 undo.ExecuteUndo ();
 461                                 return typeof (NoValueSet);
 462                         }
 463
 464                         RootContext.PopulateTypes ();
 465                         RootContext.DefineTypes ();
 466
 467                         if (Report.Errors != 0){
 468                                 undo.ExecuteUndo ();
 469                                 return typeof (NoValueSet);
 470                         }
 471
 472                         TypeBuilder tb = null;
 473                         MethodBuilder mb = null;
 474
 475                         if (host != null){
 476                                 tb = host.TypeBuilder;
 477                                 mb = null;
 478                                 foreach (MemberCore member in host.Methods){
 479                                         if (member.Name != "Host")
 480                                                 continue;
 481
 482                                         MethodOrOperator method = (MethodOrOperator) member;
 483                                         mb = method.MethodBuilder;
 484                                         break;
 485                                 }
 486
 487                                 if (mb == null)
 488                                         throw new Exception ("Internal error: did not find the method builder for the generated method");
 489                         }
 490
 491                         RootContext.EmitCode ();
 492                         if (Report.Errors != 0)
 493                                 return typeof (NoValueSet);
 494
 495                         RootContext.CloseTypes ();
 496
 497                         if (Environment.GetEnvironmentVariable ("SAVE") != null)
 498                                 CodeGen.Save (current_debug_name, false);
 499
 500                         if (host == null)
 501                                 return typeof (NoValueSet);
 502
 503                         //
 504                         // Unlike Mono, .NET requires that the MethodInfo is fetched, it cant
 505                         // work from MethodBuilders.   Retarded, I know.
 506                         //
 507                         Type tt = CodeGen.Assembly.Builder.GetType (tb.Name);
 508                         MethodInfo mi = tt.GetMethod (mb.Name);
 509
 510                         // Pull the FieldInfos from the type, and keep track of them
 511                         foreach (Field field in queued_fields){
 512                                 FieldInfo fi = tt.GetField (field.Name);
 513
 514                                 FieldInfo old = (FieldInfo) fields [field.Name];
 515
 516                                 // If a previous value was set, nullify it, so that we do
 517                                 // not leak memory
 518                                 if (old != null){
 519                                         if (old.FieldType.IsValueType){
 520                                                 //
 521                                                 // TODO: Clear fields for structs
 522                                                 //
 523                                         } else {
 524                                                 try {
 525                                                         old.SetValue (null, null);
 526                                                 } catch {
 527                                                 }
 528                                         }
 529                                 }
 530
 531                                 fields [field.Name] = fi;
 532                         }
 533                         //types.Add (tb);
 534
 535                         queued_fields.Clear ();
 536
 537                         HostSignature invoker = (HostSignature) System.Delegate.CreateDelegate (typeof (HostSignature), mi);
 538                         object retval = typeof (NoValueSet);
 539
 540                         try {
 541                                 invoke_thread = System.Threading.Thread.CurrentThread;
 542                                 invoking = true;
 543                                 invoker (ref retval);
 544                         } catch (ThreadAbortException e){
 545                                 Thread.ResetAbort ();
 546                                 Console.WriteLine ("Interrupted!\n{0}", e);
 547                         } finally {
 548                                 invoking = false;
 549                         }
 550
 551                         // d.DynamicInvoke  (new object [] { retval });
 552
 553                         return retval;
 554                 }
 555
 556                 static internal void LoadAliases (NamespaceEntry ns)
 557                 {
 558                         ns.Populate (using_alias_list, using_list);
 559                 }
 560
 561                 //
 562                 // Just a placeholder class, used as a sentinel to determine that the
 563                 // generated code did not set a value
 564                 class NoValueSet {
 565                 }
 566
 567                 static internal FieldInfo LookupField (string name)
 568                 {
 569                         FieldInfo fi =  (FieldInfo) fields [name];
 570
 571                         return fi;
 572                 }
 573
 574                 //
 575                 // Puts the FieldBuilder into a queue of names that will be
 576                 // registered.   We can not register FieldBuilders directly
 577                 // we need to fetch the FieldInfo after Reflection cooks the
 578                 // types, or bad things happen (bad means: FieldBuilders behave
 579                 // incorrectly across multiple assemblies, causing assignments to
 580                 // invalid areas
 581                 //
 582                 // This also serves for the parser to register Field classes
 583                 // that should be exposed as global variables
 584                 //
 585                 static internal void QueueField (Field f)
 586                 {
 587                         queued_fields.Add (f);
 588                 }
 589
 590                 static string Quote (string s)
 591                 {
 592                         if (s.IndexOf ('"') != -1)
 593                                 s = s.Replace ("\"", "\\\"");
 594
 595                         return "\"" + s + "\"";
 596                 }
 597
 598                 static public string GetUsing ()
 599                 {
 600                         StringBuilder sb = new StringBuilder ();
 601
 602                         foreach (object x in using_alias_list)
 603                                 sb.Append (String.Format ("using {0};\n", x));
 604
 605                         foreach (object x in using_list)
 606                                 sb.Append (String.Format ("using {0};\n", x));
 607
 608                         return sb.ToString ();
 609                 }
 610
 611                 static public string GetVars ()
 612                 {
 613                         StringBuilder sb = new StringBuilder ();
 614
 615                         foreach (DictionaryEntry de in fields){
 616                                 FieldInfo fi = LookupField ((string) de.Key);
 617                                 object value = null;
 618                                 bool error = false;
 619
 620                                 try {
 621                                         if (value == null)
 622                                                 value = "null";
 623                                         value = fi.GetValue (null);
 624                                         if (value is string)
 625                                                 value = Quote ((string)value);
 626                                 } catch {
 627                                         error = true;
 628                                 }
 629
 630                                 if (error)
 631                                         sb.Append (String.Format ("{0} {1} <error reading value>", TypeManager.CSharpName(fi.FieldType), de.Key));
 632                                 else
 633                                         sb.Append (String.Format ("{0} {1} = {2}", TypeManager.CSharpName(fi.FieldType), de.Key, value));
 634                         }
 635
 636                         return sb.ToString ();
 637                 }
 638
 639                 /// <summary>
 640                 ///    Loads the given assembly and exposes the API to the user.
 641                 /// </summary>
 642                 static public void LoadAssembly (string file)
 643                 {
 644                         Driver.LoadAssembly (file, true);
 645                 }
 646
 647                 /// <summary>
 648                 ///    Exposes the API of the given assembly to the Evaluator
 649                 /// </summary>
 650                 static public void ReferenceAssembly (Assembly a)
 651                 {
 652                         RootNamespace.Global.AddAssemblyReference (a);
 653                 }
 654
 655         }
 656
 657         /// <summary>
 658         ///   The default base class for every interaction line
 659         /// </summary>
 660         public class InteractiveBase {
 661                 public static TextWriter Output = Console.Out;
 662                 public static TextWriter Error = Console.Error;
 663                 public static string Prompt             = "csharp> ";
 664                 public static string ContinuationPrompt = "      > ";
 665
 666                 static public void ShowVars ()
 667                 {
 668                         Output.Write (Evaluator.GetVars ());
 669                         Output.Flush ();
 670                 }
 671
 672                 static public void ShowUsing ()
 673                 {
 674                         Output.Write (Evaluator.GetUsing ());
 675                         Output.Flush ();
 676                 }
 677
 678                 public delegate void Simple ();
 679
 680                 static public TimeSpan Time (Simple a)
 681                 {
 682                         DateTime start = DateTime.Now;
 683                         a ();
 684                         return DateTime.Now - start;
 685                 }
 686
 687 #if !SMCS_SOURCE
 688                 static public void LoadPackage (string pkg)
 689                 {
 690                         if (pkg == null){
 691                                 Error.WriteLine ("Invalid package specified");
 692                                 return;
 693                         }
 694
 695                         string pkgout = Driver.GetPackageFlags (pkg, false);
 696                         if (pkgout == null)
 697                                 return;
 698
 699                         string [] xargs = pkgout.Trim (new Char [] {' ', '\n', '\r', '\t'}).
 700                                 Split (new Char [] { ' ', '\t'});
 701
 702                         foreach (string s in xargs){
 703                                 if (s.StartsWith ("-r:") || s.StartsWith ("/r:") || s.StartsWith ("/reference:")){
 704                                         string lib = s.Substring (s.IndexOf (':')+1);
 705
 706                                         Driver.LoadAssembly (lib, true);
 707                                         continue;
 708                                 }
 709                         }
 710                 }
 711 #endif
 712
 713                 static public void LoadAssembly (string assembly)
 714                 {
 715                         Driver.LoadAssembly (assembly, true);
 716                 }
 717
 718                 static public string help {
 719                         get {
 720                                 return  "Static methods:\n"+
 721                                         "  LoadPackage (pkg); - Loads the given Package (like -pkg:FILE)\n" +
 722                                         "  LoadAssembly (ass) - Loads the given assembly (like -r:ASS)\n" +
 723                                         "  ShowVars ();       - Shows defined local variables.\n" +
 724                                         "  ShowUsing ();      - Show active using decltions.\n" +
 725                                         "  Prompt             - The prompt used by the C# shell\n" +
 726                                         "  ContinuationPrompt - The prompt for partial input\n" +
 727                                         "  Time(() -> { })    - Times the specified code\n" +
 728                                         "  quit;\n" +
 729                                         "  help;\n";
 730                         }
 731                 }
 732
 733                 static public object quit {
 734                         get {
 735                                 Environment.Exit (0);
 736                                 return null;
 737                         }
 738                 }
 739         }
 740
 741         //
 742         // A local variable reference that will create a Field in a
 743         // Class with the resolved type.  This is necessary so we can
 744         // support "var" as a field type in a class declaration.
 745         //
 746         // We allow LocalVariableReferece to do the heavy lifting, and
 747         // then we insert the field with the resolved type
 748         //
 749         public class LocalVariableReferenceWithClassSideEffect : LocalVariableReference {
 750                 TypeContainer container;
 751                 string name;
 752
 753                 public LocalVariableReferenceWithClassSideEffect (TypeContainer container, string name, Block current_block, string local_variable_id, Location loc)
 754                         : base (current_block, local_variable_id, loc)
 755                 {
 756                         this.container = container;
 757                         this.name = name;
 758                 }
 759
 760                 public override bool Equals (object obj)
 761                 {
 762                         LocalVariableReferenceWithClassSideEffect lvr = obj as LocalVariableReferenceWithClassSideEffect;
 763                         if (lvr == null)
 764                                 return false;
 765
 766                         if (lvr.name != name || lvr.container != container)
 767                                 return false;
 768
 769                         return base.Equals (obj);
 770                 }
 771
 772                 public override int GetHashCode ()
 773                 {
 774                         return name.GetHashCode ();
 775                 }
 776
 777                 override public Expression DoResolveLValue (EmitContext ec, Expression right_side)
 778                 {
 779                         Expression ret = base.DoResolveLValue (ec, right_side);
 780                         if (ret == null)
 781                                 return null;
 782
 783                         Field f = new Field (container, new TypeExpression (ret.Type, Location),
 784                                              Modifiers.PUBLIC | Modifiers.STATIC,
 785                                              name, null, Location);
 786                         container.AddField (f);
 787                         if (f.Define ())
 788                                 Evaluator.QueueField (f);
 789
 790                         return ret;
 791                 }
 792         }
 793
 794         /// <summary>
 795         ///    A class used to assign values if the source expression is not void
 796         ///
 797         ///    Used by the interactive shell to allow it to call this code to set
 798         ///    the return value for an invocation.
 799         /// </summary>
 800         class OptionalAssign : SimpleAssign {
 801                 public OptionalAssign (Expression t, Expression s, Location loc)
 802                         : base (t, s, loc)
 803                 {
 804                 }
 805
 806                 public override Expression DoResolve (EmitContext ec)
 807                 {
 808                         CloneContext cc = new CloneContext ();
 809                         Expression clone = source.Clone (cc);
 810
 811                         clone = clone.Resolve (ec);
 812                         if (clone == null)
 813                                 return null;
 814
 815                         // This means its really a statement.
 816                         if (clone.Type == TypeManager.void_type){
 817                                 source = source.Resolve (ec);
 818                                 target = null;
 819                                 type = TypeManager.void_type;
 820                                 eclass = ExprClass.Value;
 821                                 return this;
 822                         }
 823
 824                         return base.DoResolve (ec);
 825                 }
 826
 827                 public override void Emit (EmitContext ec)
 828                 {
 829                         if (target == null)
 830                                 source.Emit (ec);
 831                         else
 832                                 base.Emit (ec);
 833                 }
 834
 835                 public override void EmitStatement (EmitContext ec)
 836                 {
 837                         if (target == null)
 838                                 source.Emit (ec);
 839                         else
 840                                 base.EmitStatement (ec);
 841                 }
 842         }
 843
 844         public class Undo {
 845                 ArrayList undo_types;
 846
 847                 public Undo ()
 848                 {
 849                         undo_types = new ArrayList ();
 850                 }
 851
 852                 public void AddTypeContainer (TypeContainer current_container, TypeContainer tc)
 853                 {
 854                         if (current_container == tc){
 855                                 Console.Error.WriteLine ("Internal error: inserting container into itself");
 856                                 return;
 857                         }
 858
 859                         if (undo_types == null)
 860                                 undo_types = new ArrayList ();
 861                         undo_types.Add (new Pair (current_container, tc));
 862                 }
 863
 864                 public void ExecuteUndo ()
 865                 {
 866                         if (undo_types == null)
 867                                 return;
 868
 869                         foreach (Pair p in undo_types){
 870                                 TypeContainer current_container = (TypeContainer) p.First;
 871
 872                                 current_container.RemoveTypeContainer ((TypeContainer) p.Second);
 873                         }
 874                         undo_types = null;
 875                 }
 876         }
 877
 878 }
 879