src/org/ibex/js/Interpreter.java

   1 // Copyright 2004 Adam Megacz, see the COPYING file for licensing [GPL]
   2 package org.ibex.js;
   3
   4 import org.ibex.util.*;
   5 import java.util.*;
   6
   7 /** Encapsulates a single JS interpreter (ie call stack) */
   8 class Interpreter implements ByteCodes, Tokens {
   9     private static final JS CASCADE = JSString.intern("cascade");
  10
  11     // Thread-Interpreter Mapping /////////////////////////////////////////////////////////////////////////
  12
  13     static Interpreter current() { return (Interpreter)threadToInterpreter.get(Thread.currentThread()); }
  14     private static Hashtable threadToInterpreter = new Hashtable();
  15
  16
  17     // Instance members and methods //////////////////////////////////////////////////////////////////////
  18
  19     int pausecount;               ///< the number of times pause() has been invoked; -1 indicates unpauseable
  20     JSFunction f = null;          ///< the currently-executing JSFunction
  21     JSScope scope;                ///< the current top-level scope (LIFO stack via NEWSCOPE/OLDSCOPE)
  22     final Stack stack = new Stack(); ///< the object stack
  23     int pc = 0;                   ///< the program counter
  24
  25     Interpreter(JSFunction f, boolean pauseable, JSArgs args) {
  26         this.f = f;
  27         this.pausecount = pauseable ? 0 : -1;
  28         this.scope = new JSScope(f.parentScope);
  29         try {
  30             stack.push(new CallMarker());    // the "root function returned" marker -- f==null
  31             stack.push(args);
  32         } catch(JSExn e) {
  33             throw new Error("should never happen");
  34         }
  35     }
  36
  37     /** this is the only synchronization point we need in order to be threadsafe */
  38     synchronized JS resume() throws JSExn {
  39         if(f == null) throw new RuntimeException("function already finished");
  40         Thread t = Thread.currentThread();
  41         Interpreter old = (Interpreter)threadToInterpreter.get(t);
  42         threadToInterpreter.put(t, this);
  43         try {
  44             return run();
  45         } finally {
  46             if (old == null) threadToInterpreter.remove(t);
  47             else threadToInterpreter.put(t, old);
  48         }
  49     }
  50
  51     static int getLine() {
  52         Interpreter c = Interpreter.current();
  53         return c == null || c.f == null || c.pc < 0 || c.pc >= c.f.size ? -1 : c.f.line[c.pc];
  54     }
  55
  56     static String getSourceName() {
  57         Interpreter c = Interpreter.current();
  58         return c == null || c.f == null ? null : c.f.sourceName;
  59     }
  60
  61     private static JSExn je(String s) { return new JSExn(getSourceName() + ":" + getLine() + " " + s); }
  62
  63     private JS run() throws JSExn {
  64
  65         // if pausecount changes after a get/put/call, we know we've been paused
  66         final int initialPauseCount = pausecount;
  67
  68         OUTER: for(;; pc++) {
  69         try {
  70             int op = f.op[pc];
  71             Object arg = f.arg[pc];
  72             if(op == FINALLY_DONE) {
  73                 FinallyData fd = (FinallyData) stack.pop();
  74                 if(fd == null) continue OUTER; // NOP
  75                 if(fd.exn != null) throw fd.exn;
  76                 op = fd.op;
  77                 arg = fd.arg;
  78             }
  79             switch(op) {
  80             case LITERAL: stack.push((JS)arg); break;
  81             case OBJECT: stack.push(new JS.O()); break;
  82             case ARRAY: stack.push(new JSArray(JS.toInt((JS)arg))); break;
  83             case DECLARE: scope.declare((JS)(arg==null ? stack.peek() : arg)); if(arg != null) stack.push((JS)arg); break;
  84             case TOPSCOPE: stack.push(scope); break;
  85             case JT: if (JS.toBoolean(stack.pop())) pc += JS.toInt((JS)arg) - 1; break;
  86             case JF: if (!JS.toBoolean(stack.pop())) pc += JS.toInt((JS)arg) - 1; break;
  87             case JMP: pc += JS.toInt((JS)arg) - 1; break;
  88             case POP: stack.pop(); break;
  89             case SWAP: stack.swap(); break;
  90             case DUP: stack.push(stack.peek()); break;
  91             case NEWSCOPE: scope = new JSScope(scope); break;
  92             case OLDSCOPE: scope = scope.getParentScope(); break;
  93             case ASSERT: {
  94                 JS o = stack.pop();
  95                 if (JS.checkAssertions && !JS.toBoolean(o))
  96                     throw je("ibex.assertion.failed");
  97                 break;
  98             }
  99             case BITNOT: stack.push(JS.N(~JS.toLong(stack.pop()))); break;
 100             case BANG: stack.push(JS.B(!JS.toBoolean(stack.pop()))); break;
 101             case NEWFUNCTION: stack.push(((JSFunction)arg)._cloneWithNewParentScope(scope)); break;
 102             case LABEL: break;
 103
 104             case TYPEOF: {
 105                 Object o = stack.pop();
 106                 if (o == null) stack.push(null);
 107                 else if (o instanceof JSString) stack.push(JS.S("string"));
 108                 else if (o instanceof JSNumber.B) stack.push(JS.S("boolean"));
 109                 else if (o instanceof JSNumber) stack.push(JS.S("number"));
 110                 else stack.push(JS.S("object"));
 111                 break;
 112             }
 113
 114             case PUSHKEYS: {
 115                 JS o = stack.peek();
 116                 stack.push(o == null ? null : o.keys());
 117                 break;
 118             }
 119
 120             case LOOP:
 121                 stack.push(new LoopMarker(pc, pc > 0 && f.op[pc - 1] == LABEL ? (String)f.arg[pc - 1] : (String)null, scope));
 122                 stack.push(JS.T);
 123                 break;
 124
 125             case BREAK:
 126             case CONTINUE:
 127                 while(!stack.empty()) {
 128                     JS o = stack.pop();
 129                     if (o instanceof CallMarker) je("break or continue not within a loop");
 130                     if (o instanceof TryMarker) {
 131                         if(((TryMarker)o).finallyLoc < 0) continue; // no finally block, keep going
 132                         stack.push(new FinallyData(op, arg));
 133                         scope = ((TryMarker)o).scope;
 134                         pc = ((TryMarker)o).finallyLoc - 1;
 135                         continue OUTER;
 136                     }
 137                     if (o instanceof LoopMarker) {
 138                         if (arg == null || arg.equals(((LoopMarker)o).label)) {
 139                             int loopInstructionLocation = ((LoopMarker)o).location;
 140                             int endOfLoop = JS.toInt((JS)f.arg[loopInstructionLocation]) + loopInstructionLocation;
 141                             scope = ((LoopMarker)o).scope;
 142                             if (op == CONTINUE) { stack.push(o); stack.push(JS.F); }
 143                             pc = op == BREAK ? endOfLoop - 1 : loopInstructionLocation;
 144                             continue OUTER;
 145                         }
 146                     }
 147                 }
 148                 throw new Error("CONTINUE/BREAK invoked but couldn't find LoopMarker at " +
 149                                 getSourceName() + ":" + getLine());
 150
 151             case TRY: {
 152                 int[] jmps = (int[]) arg;
 153                 // jmps[0] is how far away the catch block is, jmps[1] is how far away the finally block is
 154                 // each can be < 0 if the specified block does not exist
 155                 stack.push(new TryMarker(jmps[0] < 0 ? -1 : pc + jmps[0], jmps[1] < 0 ? -1 : pc + jmps[1], this));
 156                 break;
 157             }
 158
 159             case RETURN: {
 160                 JS retval = stack.pop();
 161                 while(!stack.empty()) {
 162                     Object o = stack.pop();
 163                     if (o instanceof TryMarker) {
 164                         if(((TryMarker)o).finallyLoc < 0) continue;
 165                         stack.push(retval);
 166                         stack.push(new FinallyData(RETURN));
 167                         scope = ((TryMarker)o).scope;
 168                         pc = ((TryMarker)o).finallyLoc - 1;
 169                         continue OUTER;
 170                     } else if (o instanceof CallMarker) {
 171                         if (o instanceof TrapMarker) { // handles return component of a read trap
 172                             TrapMarker tm = (TrapMarker) o;
 173                             boolean cascade = tm.t.isWriteTrap() && !tm.cascadeHappened && !JS.toBoolean(retval);
 174                             if(cascade) {
 175                                 Trap t = tm.t.nextWriteTrap();
 176                                 if(t == null && tm.target instanceof JS.Clone) {
 177                                     tm.target = ((JS.Clone)tm.target).clonee;
 178                                     t = tm.target.getTrap(tm.key);
 179                                     if(t != null) t = t.writeTrap();
 180                                 }
 181                                 if(t != null) {
 182                                     tm.t = t; // we reuse the old trap marker
 183                                     setupTrap(t,tm.val,tm);
 184                                     pc--; // we increment it on the next iter
 185                                     continue OUTER;
 186                                 } else {
 187                                     tm.target.put(tm.key,tm.val);
 188                                 }
 189                             }
 190                         }
 191                         CallMarker cm = (CallMarker) o;
 192                         scope = cm.scope;
 193                         pc = cm.pc - 1;
 194                         f = cm.f;
 195                         stack.push(retval);
 196                         if (pausecount > initialPauseCount) { pc++; return null; }   // we were paused
 197                         if(f == null) return retval;
 198                         continue OUTER;
 199                     }
 200                 }
 201                 throw new Error("error: RETURN invoked but couldn't find a CallMarker!");
 202             }
 203
 204             case PUT: {
 205                 JS val = stack.pop();
 206                 JS key = stack.pop();
 207                 JS target = stack.peek();
 208                 if (target == null) throw je("tried to put " + JS.debugToString(val) + " to the " + JS.debugToString(key) + " property on the null value");
 209                 if (key == null) throw je("tried to assign \"" + JS.debugToString(val) + "\" to the null key");
 210
 211                 Trap t = null;
 212                 TrapMarker tm = null;
 213                 if(target instanceof JSScope && key.jsequals(CASCADE)) {
 214                     CallMarker o = stack.findCall();
 215                     if(o instanceof TrapMarker) {
 216                         tm = (TrapMarker) o;
 217                         target = tm.target;
 218                         key = tm.key;
 219                         tm.cascadeHappened = true;
 220                         t = tm.t;
 221                         if(t.isReadTrap()) throw new JSExn("can't do a write cascade in a read trap");
 222                         t = t.nextWriteTrap();
 223                     }
 224                 }
 225                 if(tm == null) { // not cascading
 226                     t = target instanceof JSScope ? t = ((JSScope)target).top().getTrap(key) : target.getTrap(key);
 227                     if(t != null) t = t.writeTrap();
 228                 }
 229                 if(t == null && target instanceof JS.Clone) {
 230                     target = ((JS.Clone)target).clonee;
 231                     t = target.getTrap(key);
 232                     if(t != null) t = t.writeTrap();
 233                 }
 234
 235                 stack.push(val);
 236
 237                 if(t != null) {
 238                     setupTrap(t,val,new TrapMarker(this,t,target,key,val));
 239                     pc--; // we increment later
 240                     break;
 241                 } else {
 242                     target.put(key,val);
 243                     if (pausecount > initialPauseCount) { pc++; return null; }   // we were paused
 244                     break;
 245                 }
 246             }
 247
 248             case GET:
 249             case GET_PRESERVE: {
 250                 JS target, key;
 251                 if (op == GET) {
 252                     key = arg == null ? stack.pop() : (JS)arg;
 253                     target = stack.pop();
 254                 } else {
 255                     key = stack.pop();
 256                     target = stack.peek();
 257                     stack.push(key);
 258                 }
 259                 JS ret = null;
 260                 if (key == null) throw je("tried to get the null key from " + target);
 261                 if (target == null) throw je("tried to get property \"" + key + "\" from the null object");
 262
 263                 Trap t = null;
 264                 TrapMarker tm = null;
 265                 if(target instanceof JSScope && key.jsequals(CASCADE)) {
 266                     CallMarker o = stack.findCall();
 267                     if(o instanceof TrapMarker) {
 268                         tm = (TrapMarker) o;
 269                         target = tm.target;
 270                         key = tm.key;
 271                         t = tm.t;
 272                         if(t.isWriteTrap()) throw new JSExn("can't do a read cascade in a write trap");
 273                         t = t.nextReadTrap();
 274                     }
 275                 }
 276                 if(tm == null) { // not cascading
 277                     t = target instanceof JSScope ? t = ((JSScope)target).top().getTrap(key) : ((JS)target).getTrap(key);
 278                     if(t != null) t = t.readTrap();
 279                 }
 280                 if(t == null && target instanceof JS.Clone) {
 281                     target = ((JS.Clone)target).clonee;
 282                     t = target.getTrap(key);
 283                     if(t != null) t = t.readTrap();
 284                 }
 285
 286                 if(t != null) {
 287                     setupTrap(t,null,new TrapMarker(this,t,target,key,null));
 288                     pc--; // we increment later
 289                     break;
 290                 } else {
 291                     ret = target.get(key);
 292                     if (pausecount > initialPauseCount) { pc++; return null; }   // we were paused
 293                     if (ret == JS.METHOD) ret = new Stub(target, key);
 294                     stack.push(ret);
 295                     break;
 296                 }
 297             }
 298
 299             case CALL: case CALLMETHOD: {
 300                 int numArgs = JS.toInt((JS)arg);
 301
 302                 JS[] rest = numArgs > 3 ? new JS[numArgs - 3] : null;
 303                 for(int i=numArgs - 1; i>2; i--) rest[i-3] = stack.pop();
 304                 JS a2 = numArgs <= 2 ? null : stack.pop();
 305                 JS a1 = numArgs <= 1 ? null : stack.pop();
 306                 JS a0 = numArgs <= 0 ? null : stack.pop();
 307
 308                 JS method = null;
 309                 JS ret = null;
 310                 JS object = stack.pop();
 311
 312                 if (op == CALLMETHOD) {
 313                     if (object == JS.METHOD) {
 314                         method = stack.pop();
 315                         object = stack.pop();
 316                     } else if (object == null) {
 317                         method = stack.pop();
 318                         object = stack.pop();
 319                         throw new JSExn("function '"+JS.debugToString(method)+"' not found in " + object.getClass().getName());
 320                     } else {
 321                         stack.pop();
 322                         stack.pop();
 323                     }
 324                 }
 325
 326                 if (object instanceof JSFunction) {
 327                     stack.push(new CallMarker(this));
 328                     stack.push(new JSArgs(a0,a1,a2,rest,numArgs,object));
 329                     f = (JSFunction)object;
 330                     scope = new JSScope(f.parentScope);
 331                     pc = -1;
 332                     break;
 333                 } else {
 334                     JS c = (JS)object;
 335                     ret = method == null ? c.call(a0, a1, a2, rest, numArgs) : c.callMethod(method, a0, a1, a2, rest, numArgs);
 336                 }
 337
 338                 if (pausecount > initialPauseCount) { pc++; return null; }
 339                 stack.push(ret);
 340                 break;
 341             }
 342
 343             case THROW:
 344                 throw new JSExn(stack.pop(), this);
 345
 346                 /* FIXME GRAMMAR
 347             case MAKE_GRAMMAR: {
 348                 final Grammar r = (Grammar)arg;
 349                 final JSScope final_scope = scope;
 350                 Grammar r2 = new Grammar() {
 351                         public int match(String s, int start, Hash v, JSScope scope) throws JSExn {
 352                             return r.match(s, start, v, final_scope);
 353                         }
 354                         public int matchAndWrite(String s, int start, Hash v, JSScope scope, String key) throws JSExn {
 355                             return r.matchAndWrite(s, start, v, final_scope, key);
 356                         }
 357                         public Object call(Object a0, Object a1, Object a2, Object[] rest, int nargs) throws JSExn {
 358                             Hash v = new Hash();
 359                             r.matchAndWrite((String)a0, 0, v, final_scope, "foo");
 360                             return v.get("foo");
 361                         }
 362                     };
 363                 Object obj = stack.pop();
 364                 if (obj != null && obj instanceof Grammar) r2 = new Grammar.Alternative((Grammar)obj, r2);
 365                 stack.push(r2);
 366                 break;
 367             }
 368                 */
 369             case ADD_TRAP: case DEL_TRAP: {
 370                 JS val = stack.pop();
 371                 JS key = stack.pop();
 372                 JS js = stack.peek();
 373                 // A trap addition/removal
 374                 if(!(val instanceof JSFunction)) throw new JSExn("tried to add/remove a non-function trap");
 375                 if(js instanceof JSScope) {
 376                     JSScope s = (JSScope) js;
 377                     while(s.getParentScope() != null) {
 378                         if(s.has(key)) throw new JSExn("cannot trap a variable that isn't at the top level scope");
 379                         s = s.getParentScope();
 380                     }
 381                     js = s;
 382                 }
 383                 if(op == ADD_TRAP) js.addTrap(key, (JSFunction)val);
 384                 else js.delTrap(key, (JSFunction)val);
 385                 break;
 386             }
 387
 388             case ADD: {
 389                 int count = ((JSNumber)arg).toInt();
 390                 if(count < 2) throw new Error("this should never happen");
 391                 if(count == 2) {
 392                     // common case
 393                     JS right = stack.pop();
 394                     JS left = stack.pop();
 395                     JS ret;
 396                     if(left instanceof JSString || right instanceof JSString)
 397                         ret = JS.S(JS.toString(left).concat(JS.toString(right)));
 398                     else if(left instanceof JSNumber.D || right instanceof JSNumber.D)
 399                         ret = JS.N(JS.toDouble(left) + JS.toDouble(right));
 400                     else {
 401                         long l = JS.toLong(left) + JS.toLong(right);
 402                         if(l < Integer.MIN_VALUE || l > Integer.MAX_VALUE) ret = JS.N(l);
 403                         ret = JS.N((int)l);
 404                     }
 405                     stack.push(ret);
 406                 } else {
 407                     JS[] args = new JS[count];
 408                     while(--count >= 0) args[count] = stack.pop();
 409                     if(args[0] instanceof JSString) {
 410                         StringBuffer sb = new StringBuffer(64);
 411                         for(int i=0;i<args.length;i++) sb.append(JS.toString(args[i]));
 412                         stack.push(JS.S(sb.toString()));
 413                     } else {
 414                         int numStrings = 0;
 415                         for(int i=0;i<args.length;i++) if(args[i] instanceof JSString) numStrings++;
 416                         if(numStrings == 0) {
 417                             double d = 0.0;
 418                             for(int i=0;i<args.length;i++) d += JS.toDouble(args[i]);
 419                             stack.push(JS.N(d));
 420                         } else {
 421                             int i=0;
 422                             StringBuffer sb = new StringBuffer(64);
 423                             if(!(args[0] instanceof JSString || args[1] instanceof JSString)) {
 424                                 double d=0.0;
 425                                 do {
 426                                     d += JS.toDouble(args[i++]);
 427                                 } while(!(args[i] instanceof JSString));
 428                                 sb.append(JS.toString(JS.N(d)));
 429                             }
 430                             while(i < args.length) sb.append(JS.toString(args[i++]));
 431                             stack.push(JS.S(sb.toString()));
 432                         }
 433                     }
 434                 }
 435                 break;
 436             }
 437
 438             default: {
 439                 JS right = stack.pop();
 440                 JS left = stack.pop();
 441                 switch(op) {
 442
 443                 case BITOR: stack.push(JS.N(JS.toLong(left) | JS.toLong(right))); break;
 444                 case BITXOR: stack.push(JS.N(JS.toLong(left) ^ JS.toLong(right))); break;
 445                 case BITAND: stack.push(JS.N(JS.toLong(left) & JS.toLong(right))); break;
 446
 447                 case SUB: stack.push(JS.N(JS.toDouble(left) - JS.toDouble(right))); break;
 448                 case MUL: stack.push(JS.N(JS.toDouble(left) * JS.toDouble(right))); break;
 449                 case DIV: stack.push(JS.N(JS.toDouble(left) / JS.toDouble(right))); break;
 450                 case MOD: stack.push(JS.N(JS.toDouble(left) % JS.toDouble(right))); break;
 451
 452                 case LSH: stack.push(JS.N(JS.toLong(left) << JS.toLong(right))); break;
 453                 case RSH: stack.push(JS.N(JS.toLong(left) >> JS.toLong(right))); break;
 454                 case URSH: stack.push(JS.N(JS.toLong(left) >>> JS.toLong(right))); break;
 455
 456                 //#repeat </<=/>/>= LT/LE/GT/GE
 457                 case LT: {
 458                     if(left instanceof JSString && right instanceof JSString)
 459                         stack.push(JS.B(JS.toString(left).compareTo(JS.toString(right)) < 0));
 460                     else
 461                         stack.push(JS.B(JS.toDouble(left) < JS.toDouble(right)));
 462                 }
 463                 //#end
 464
 465                 case EQ:
 466                 case NE: {
 467                     boolean ret;
 468                     if(left == null && right == null) ret = true;
 469                     else if(left == null || right == null) ret = false;
 470                     else ret = left.jsequals(right);
 471                     stack.push(JS.B(op == EQ ? ret : !ret)); break;
 472                 }
 473
 474                 default: throw new Error("unknown opcode " + op);
 475                 } }
 476             }
 477
 478         } catch(JSExn e) {
 479             catchException(e);
 480             pc--; // it'll get incremented on the next iteration
 481         } // end try/catch
 482         } // end for
 483     }
 484
 485     /** tries to find a handler withing the call chain for this exception
 486         if a handler is found the interpreter is setup to call the exception handler
 487         if a handler is not found the exception is thrown
 488     */
 489     void catchException(JSExn e) throws JSExn {
 490         while(!stack.empty()) {
 491             JS o = stack.pop();
 492             if (o instanceof CatchMarker || o instanceof TryMarker) {
 493                 boolean inCatch = o instanceof CatchMarker;
 494                 if(inCatch) {
 495                     o = stack.pop();
 496                     if(((TryMarker)o).finallyLoc < 0) continue; // no finally block, keep going
 497                 }
 498                 if(!inCatch && ((TryMarker)o).catchLoc >= 0) {
 499                     // run the catch block, this will implicitly run the finally block, if it exists
 500                     stack.push(o);
 501                     stack.push(catchMarker);
 502                     stack.push(e.getObject());
 503                     f = ((TryMarker)o).f;
 504                     scope = ((TryMarker)o).scope;
 505                     pc = ((TryMarker)o).catchLoc;
 506                     return;
 507                 } else {
 508                     stack.push(new FinallyData(e));
 509                     f = ((TryMarker)o).f;
 510                     scope = ((TryMarker)o).scope;
 511                     pc = ((TryMarker)o).finallyLoc;
 512                     return;
 513                 }
 514             }
 515         }
 516         throw e;
 517     }
 518
 519     void setupTrap(Trap t, JS val, CallMarker cm) throws JSExn {
 520         stack.push(cm);
 521         stack.push(t.isWriteTrap() ? new JSArgs(val,t.f) : new JSArgs(t.f));
 522         f = t.f;
 523         scope = new TrapScope(t.f.parentScope,t.target,t.f,t.key);
 524         pc = 0;
 525     }
 526
 527
 528     // Markers //////////////////////////////////////////////////////////////////////
 529
 530     static class Marker extends JS {
 531         public JS get(JS key) throws JSExn { throw new Error("this should not be accessible from a script"); }
 532         public void put(JS key, JS val) throws JSExn { throw new Error("this should not be accessible from a script"); }
 533         public String coerceToString() { throw new Error("this should not be accessible from a script"); }
 534         public JS call(JS a0, JS a1, JS a2, JS[] rest, int nargs) throws JSExn { throw new Error("this should not be accessible from a script"); }
 535     }
 536
 537     static class CallMarker extends Marker {
 538         final int pc;
 539         final JSScope scope;
 540         final JSFunction f;
 541         public CallMarker(Interpreter cx) { pc = cx.pc + 1; scope = cx.scope; f = cx.f; }
 542         public CallMarker() { pc = -1; scope = null; f = null; }
 543     }
 544
 545     static class TrapMarker extends CallMarker {
 546         Trap t;
 547         JS target;
 548         final JS key;
 549         final JS val;
 550         boolean cascadeHappened;
 551         public TrapMarker(Interpreter cx, Trap t, JS target, JS key, JS val) {
 552             super(cx);
 553             this.t = t;
 554             this.target = target;
 555             this.key = key;
 556             this.val = val;
 557         }
 558     }
 559
 560     static class CatchMarker extends Marker { }
 561     private static CatchMarker catchMarker = new CatchMarker();
 562
 563     static class LoopMarker extends Marker {
 564         final public int location;
 565         final public String label;
 566         final public JSScope scope;
 567         public LoopMarker(int location, String label, JSScope scope) {
 568             this.location = location;
 569             this.label = label;
 570             this.scope = scope;
 571         }
 572     }
 573     static class TryMarker extends Marker {
 574         final public int catchLoc;
 575         final public int finallyLoc;
 576         final public JSScope scope;
 577         final public JSFunction f;
 578         public TryMarker(int catchLoc, int finallyLoc, Interpreter cx) {
 579             this.catchLoc = catchLoc;
 580             this.finallyLoc = finallyLoc;
 581             this.scope = cx.scope;
 582             this.f = cx.f;
 583         }
 584     }
 585     static class FinallyData extends Marker {
 586         final public int op;
 587         final public Object arg;
 588         final public JSExn exn;
 589         public FinallyData(int op) { this(op,null); }
 590         public FinallyData(int op, Object arg) { this.op = op; this.arg = arg; this.exn = null; }
 591         public FinallyData(JSExn exn) { this.exn = exn; this.op = -1; this.arg = null; } // Just throw this exn
 592     }
 593
 594     static class TrapScope extends JSScope {
 595         JS trapee;
 596         JS callee;
 597         JS trapname;
 598         public TrapScope(JSScope parent, JS trapee, JS callee, JS trapname) {
 599             super(parent); this.trapee = trapee; this.callee = callee; this.trapname = trapname;
 600         }
 601         public JS get(JS key) throws JSExn {
 602             if(JS.isString(key)) {
 603                 //#switch(JS.toString(key))
 604                 case "trapee": return trapee;
 605                 case "callee": return callee;
 606                 case "trapname": return trapname;
 607                 //#end
 608             }
 609             return super.get(key);
 610         }
 611     }
 612
 613     static class JSArgs extends JS {
 614         private final JS a0;
 615         private final JS a1;
 616         private final JS a2;
 617         private final JS[] rest;
 618         private final int nargs;
 619         private final JS callee;
 620
 621         public JSArgs(JS callee) { this(null,null,null,null,0,callee); }
 622         public JSArgs(JS a0, JS callee) { this(a0,null,null,null,1,callee); }
 623         public JSArgs(JS a0, JS a1, JS a2, JS[] rest, int nargs, JS callee) {
 624             this.a0 = a0; this.a1 = a1; this.a2 = a2;
 625             this.rest = rest; this.nargs = nargs;
 626             this.callee = callee;
 627         }
 628
 629         public JS get(JS key) throws JSExn {
 630             if(JS.isInt(key)) {
 631                 int n = JS.toInt(key);
 632                 switch(n) {
 633                     case 0: return a0;
 634                     case 1: return a1;
 635                     case 2: return a2;
 636                     default: return n>= 0 && n < nargs ? rest[n-3] : null;
 637                 }
 638             }
 639             //#switch(JS.toString(key))
 640             case "callee": return callee;
 641             case "length": return JS.N(nargs);
 642             //#end
 643             return super.get(key);
 644         }
 645     }
 646
 647     static class Stub extends JS {
 648         private JS method;
 649         JS obj;
 650         public Stub(JS obj, JS method) { this.obj = obj; this.method = method; }
 651         public JS call(JS a0, JS a1, JS a2, JS[] rest, int nargs) throws JSExn {
 652             return ((JS)obj).callMethod(method, a0, a1, a2, rest, nargs);
 653         }
 654     }
 655
 656     static class Stack {
 657         private static final int MAX_STACK_SIZE = 512;
 658         private JS[] stack = new JS[64];
 659         private int sp = 0;
 660
 661         boolean empty() { return sp == 0; }
 662         void push(JS o) throws JSExn { if(sp == stack.length) grow(); stack[sp++] = o; }
 663         JS peek() { if(sp == 0) throw new RuntimeException("Stack underflow"); return stack[sp-1]; }
 664         final JS pop() { if(sp == 0) throw new RuntimeException("Stack underflow"); return stack[--sp]; }
 665         void swap() throws JSExn {
 666             if(sp < 2) throw new JSExn("stack overflow");
 667             JS tmp = stack[sp-2];
 668             stack[sp-2] = stack[sp-1];
 669             stack[sp-1] = tmp;
 670         }
 671         CallMarker findCall() {
 672             for(int i=sp-1;i>=0;i--) if(stack[i] instanceof CallMarker) return (CallMarker) stack[i];
 673             return null;
 674         }
 675         void grow() throws JSExn {
 676             if(stack.length >= MAX_STACK_SIZE) throw new JSExn("Stack overflow");
 677             JS[] stack2 = new JS[stack.length * 2];
 678             System.arraycopy(stack,0,stack2,0,stack.length);
 679         }
 680
 681         void backtrace(JSExn e) {
 682             for(int i=sp-1;i>=0;i--) {
 683                 if (stack[i] instanceof CallMarker) {
 684                     CallMarker cm = (CallMarker)stack[i];
 685                     if(cm.f == null) break;
 686                     String s = cm.f.sourceName + ":" + cm.f.line[cm.pc-1];
 687                     if(cm instanceof Interpreter.TrapMarker)
 688                         s += " (trap on " + JS.debugToString(((Interpreter.TrapMarker)cm).key) + ")";
 689                     e.addBacktrace(s);
 690                 }
 691             }
 692         }
 693     }
 694 }