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(null));    // 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     Interpreter(Trap t, JS val, boolean pauseOnPut) {
  38         this.pausecount = -1;
  39         try {
  40             setupTrap(t,val,new TrapMarker(null,t,val,pauseOnPut));
  41         } catch(JSExn e) {
  42             throw new Error("should never happen");
  43         }
  44     }
  45
  46     /** this is the only synchronization point we need in order to be threadsafe */
  47     synchronized JS resume() throws JSExn {
  48         if(f == null) throw new RuntimeException("function already finished");
  49         Thread t = Thread.currentThread();
  50         Interpreter old = (Interpreter)threadToInterpreter.get(t);
  51         threadToInterpreter.put(t, this);
  52         try {
  53             return run();
  54         } finally {
  55             if (old == null) threadToInterpreter.remove(t);
  56             else threadToInterpreter.put(t, old);
  57         }
  58     }
  59
  60     static int getLine() {
  61         Interpreter c = Interpreter.current();
  62         return c == null || c.f == null || c.pc < 0 || c.pc >= c.f.size ? -1 : c.f.line[c.pc];
  63     }
  64
  65     static String getSourceName() {
  66         Interpreter c = Interpreter.current();
  67         return c == null || c.f == null ? null : c.f.sourceName;
  68     }
  69
  70     private static JSExn je(String s) { return new JSExn(getSourceName() + ":" + getLine() + " " + s); }
  71
  72     private JS run() throws JSExn {
  73
  74         // if pausecount changes after a get/put/call, we know we've been paused
  75         final int initialPauseCount = pausecount;
  76
  77         OUTER: for(;; pc++) {
  78         try {
  79             int op = f.op[pc];
  80             Object arg = f.arg[pc];
  81             if(op == FINALLY_DONE) {
  82                 FinallyData fd = (FinallyData) stack.pop();
  83                 if(fd == null) continue OUTER; // NOP
  84                 if(fd.exn != null) throw fd.exn;
  85                 op = fd.op;
  86                 arg = fd.arg;
  87             }
  88             switch(op) {
  89             case LITERAL: stack.push((JS)arg); break;
  90             case OBJECT: stack.push(new JS.O()); break;
  91             case ARRAY: stack.push(new JSArray(JS.toInt((JS)arg))); break;
  92             case DECLARE: scope.declare((JS)(arg==null ? stack.peek() : arg)); if(arg != null) stack.push((JS)arg); break;
  93             case TOPSCOPE: stack.push(scope); break;
  94             case JT: if (JS.toBoolean(stack.pop())) pc += JS.toInt((JS)arg) - 1; break;
  95             case JF: if (!JS.toBoolean(stack.pop())) pc += JS.toInt((JS)arg) - 1; break;
  96             case JMP: pc += JS.toInt((JS)arg) - 1; break;
  97             case POP: stack.pop(); break;
  98             case SWAP: stack.swap(); break;
  99             case DUP: stack.push(stack.peek()); break;
 100             case NEWSCOPE: scope = new JSScope(scope); break;
 101             case OLDSCOPE: scope = scope.getParentScope(); break;
 102             case ASSERT: {
 103                 JS o = stack.pop();
 104                 if (JS.checkAssertions && !JS.toBoolean(o))
 105                     throw je("ibex.assertion.failed");
 106                 break;
 107             }
 108             case BITNOT: stack.push(JS.N(~JS.toLong(stack.pop()))); break;
 109             case BANG: stack.push(JS.B(!JS.toBoolean(stack.pop()))); break;
 110             case NEWFUNCTION: stack.push(((JSFunction)arg)._cloneWithNewParentScope(scope)); break;
 111             case LABEL: break;
 112
 113             case TYPEOF: {
 114                 Object o = stack.pop();
 115                 if (o == null) stack.push(null);
 116                 else if (o instanceof JSString) stack.push(JS.S("string"));
 117                 else if (o instanceof JSNumber.B) stack.push(JS.S("boolean"));
 118                 else if (o instanceof JSNumber) stack.push(JS.S("number"));
 119                 else stack.push(JS.S("object"));
 120                 break;
 121             }
 122
 123             case PUSHKEYS: {
 124                 JS o = stack.peek();
 125                 stack.push(o == null ? null : o.keys());
 126                 break;
 127             }
 128
 129             case LOOP:
 130                 stack.push(new LoopMarker(pc, pc > 0 && f.op[pc - 1] == LABEL ? (String)f.arg[pc - 1] : (String)null, scope));
 131                 stack.push(JS.T);
 132                 break;
 133
 134             case BREAK:
 135             case CONTINUE:
 136                 while(!stack.empty()) {
 137                     JS o = stack.pop();
 138                     if (o instanceof CallMarker) je("break or continue not within a loop");
 139                     if (o instanceof TryMarker) {
 140                         if(((TryMarker)o).finallyLoc < 0) continue; // no finally block, keep going
 141                         stack.push(new FinallyData(op, arg));
 142                         scope = ((TryMarker)o).scope;
 143                         pc = ((TryMarker)o).finallyLoc - 1;
 144                         continue OUTER;
 145                     }
 146                     if (o instanceof LoopMarker) {
 147                         if (arg == null || arg.equals(((LoopMarker)o).label)) {
 148                             int loopInstructionLocation = ((LoopMarker)o).location;
 149                             int endOfLoop = JS.toInt((JS)f.arg[loopInstructionLocation]) + loopInstructionLocation;
 150                             scope = ((LoopMarker)o).scope;
 151                             if (op == CONTINUE) { stack.push(o); stack.push(JS.F); }
 152                             pc = op == BREAK ? endOfLoop - 1 : loopInstructionLocation;
 153                             continue OUTER;
 154                         }
 155                     }
 156                 }
 157                 throw new Error("CONTINUE/BREAK invoked but couldn't find LoopMarker at " +
 158                                 getSourceName() + ":" + getLine());
 159
 160             case TRY: {
 161                 int[] jmps = (int[]) arg;
 162                 // jmps[0] is how far away the catch block is, jmps[1] is how far away the finally block is
 163                 // each can be < 0 if the specified block does not exist
 164                 stack.push(new TryMarker(jmps[0] < 0 ? -1 : pc + jmps[0], jmps[1] < 0 ? -1 : pc + jmps[1], this));
 165                 break;
 166             }
 167
 168             case RETURN: {
 169                 JS retval = stack.pop();
 170                 while(!stack.empty()) {
 171                     Object o = stack.pop();
 172                     if (o instanceof TryMarker) {
 173                         if(((TryMarker)o).finallyLoc < 0) continue;
 174                         stack.push(retval);
 175                         stack.push(new FinallyData(RETURN));
 176                         scope = ((TryMarker)o).scope;
 177                         pc = ((TryMarker)o).finallyLoc - 1;
 178                         continue OUTER;
 179                     } else if (o instanceof CallMarker) {
 180                         boolean didTrapPut = false;
 181                         if (o instanceof TrapMarker) { // handles return component of a read trap
 182                             TrapMarker tm = (TrapMarker) o;
 183                             boolean cascade = tm.t.isWriteTrap() && !tm.cascadeHappened && !JS.toBoolean(retval);
 184                             if(cascade) {
 185                                 Trap t = tm.t.nextWriteTrap();
 186                                 if(t == null && tm.t.target instanceof JS.Clone) {
 187                                     t = ((JS.Clone)tm.t.target).clonee.getTrap(tm.t.key);
 188                                     if(t != null) t = t.writeTrap();
 189                                 }
 190                                 if(t != null) {
 191                                     tm.t = t; // we reuse the old trap marker
 192                                     setupTrap(t,tm.val,tm);
 193                                     pc--; // we increment it on the next iter
 194                                     continue OUTER;
 195                                 } else {
 196                                     didTrapPut = true;
 197                                     if(!tm.pauseOnPut) tm.t.target.put(tm.t.key,tm.val);
 198                                 }
 199                             }
 200                         }
 201                         CallMarker cm = (CallMarker) o;
 202                         scope = cm.scope;
 203                         pc = cm.pc - 1;
 204                         f = cm.f;
 205                         if (didTrapPut) {
 206                             if (((TrapMarker)cm).pauseOnPut) { pc++; return ((TrapMarker)cm).val; }
 207                             if (pausecount > initialPauseCount) { pc++; return null; }   // we were paused
 208                         } else {
 209                             stack.push(retval);
 210                         }
 211                         if (f == null) return retval;
 212                         continue OUTER;
 213                     }
 214                 }
 215                 throw new Error("error: RETURN invoked but couldn't find a CallMarker!");
 216             }
 217
 218             case PUT: {
 219                 JS val = stack.pop();
 220                 JS key = stack.pop();
 221                 JS target = stack.peek();
 222                 if (target == null) throw je("tried to put " + JS.debugToString(val) + " to the " + JS.debugToString(key) + " property on the null value");
 223                 if (key == null) throw je("tried to assign \"" + JS.debugToString(val) + "\" to the null key");
 224
 225                 Trap t = null;
 226                 TrapMarker tm = null;
 227                 if(target instanceof JSScope && key.jsequals(CASCADE)) {
 228                     CallMarker o = stack.findCall();
 229                     if(o instanceof TrapMarker) {
 230                         tm = (TrapMarker) o;
 231                         target = tm.t.target;
 232                         key = tm.t.key;
 233                         tm.cascadeHappened = true;
 234                         t = tm.t;
 235                         if(t.isReadTrap()) throw new JSExn("can't do a write cascade in a read trap");
 236                         t = t.nextWriteTrap();
 237                     }
 238                 }
 239                 if(tm == null) { // not cascading
 240                     t = target instanceof JSScope ? t = ((JSScope)target).top().getTrap(key) : target.getTrap(key);
 241                     if(t != null) t = t.writeTrap();
 242                 }
 243                 if(t == null && target instanceof JS.Clone) {
 244                     target = ((JS.Clone)target).clonee;
 245                     t = target.getTrap(key);
 246                     if(t != null) t = t.writeTrap();
 247                 }
 248
 249                 stack.push(val);
 250
 251                 if(t != null) {
 252                     setupTrap(t,val,new TrapMarker(this,t,val, tm != null && tm.pauseOnPut));
 253                     pc--; // we increment later
 254                     break;
 255                 } else {
 256                     if (tm != null && tm.pauseOnPut) { pc++; return val; }
 257                     target.put(key,val);
 258                     if (pausecount > initialPauseCount) { pc++; return null; }   // we were paused
 259                     break;
 260                 }
 261             }
 262
 263             case GET:
 264             case GET_PRESERVE: {
 265                 JS target, key;
 266                 if (op == GET) {
 267                     key = arg == null ? stack.pop() : (JS)arg;
 268                     target = stack.pop();
 269                 } else {
 270                     key = stack.pop();
 271                     target = stack.peek();
 272                     stack.push(key);
 273                 }
 274                 JS ret = null;
 275                 if (key == null) throw je("tried to get the null key from " + target);
 276                 if (target == null) throw je("tried to get property \"" + key + "\" from the null object");
 277
 278                 Trap t = null;
 279                 TrapMarker tm = null;
 280                 if(target instanceof JSScope && key.jsequals(CASCADE)) {
 281                     CallMarker o = stack.findCall();
 282                     if(o instanceof TrapMarker) {
 283                         tm = (TrapMarker) o;
 284                         target = tm.t.target;
 285                         key = tm.t.key;
 286                         t = tm.t;
 287                         if(t.isWriteTrap()) throw new JSExn("can't do a read cascade in a write trap");
 288                         t = t.nextReadTrap();
 289                     }
 290                 }
 291                 if(tm == null) { // not cascading
 292                     t = target instanceof JSScope ? t = ((JSScope)target).top().getTrap(key) : ((JS)target).getTrap(key);
 293                     if(t != null) t = t.readTrap();
 294                 }
 295                 if(t == null && target instanceof JS.Clone) {
 296                     target = ((JS.Clone)target).clonee;
 297                     t = target.getTrap(key);
 298                     if(t != null) t = t.readTrap();
 299                 }
 300
 301                 if(t != null) {
 302                     setupTrap(t,null,new TrapMarker(this,t,null));
 303                     pc--; // we increment later
 304                     break;
 305                 } else {
 306                     ret = target.get(key);
 307                     if (pausecount > initialPauseCount) { pc++; return null; }   // we were paused
 308                     if (ret == JS.METHOD) ret = new Stub(target, key);
 309                     stack.push(ret);
 310                     break;
 311                 }
 312             }
 313
 314             case CALL: case CALLMETHOD: {
 315                 int numArgs = JS.toInt((JS)arg);
 316
 317                 JS[] rest = numArgs > 3 ? new JS[numArgs - 3] : null;
 318                 for(int i=numArgs - 1; i>2; i--) rest[i-3] = stack.pop();
 319                 JS a2 = numArgs <= 2 ? null : stack.pop();
 320                 JS a1 = numArgs <= 1 ? null : stack.pop();
 321                 JS a0 = numArgs <= 0 ? null : stack.pop();
 322
 323                 JS method = null;
 324                 JS ret = null;
 325                 JS object = stack.pop();
 326
 327                 if (op == CALLMETHOD) {
 328                     if (object == JS.METHOD) {
 329                         method = stack.pop();
 330                         object = stack.pop();
 331                     } else if (object == null) {
 332                         method = stack.pop();
 333                         object = stack.pop();
 334                         throw new JSExn("function '"+JS.debugToString(method)+"' not found in " + object.getClass().getName());
 335                     } else {
 336                         stack.pop();
 337                         stack.pop();
 338                     }
 339                 }
 340
 341                 if (object instanceof JSFunction) {
 342                     stack.push(new CallMarker(this));
 343                     stack.push(new JSArgs(a0,a1,a2,rest,numArgs,object));
 344                     f = (JSFunction)object;
 345                     scope = new JSScope(f.parentScope);
 346                     pc = -1;
 347                     break;
 348                 } else {
 349                     JS c = (JS)object;
 350                     ret = method == null ? c.call(a0, a1, a2, rest, numArgs) : c.callMethod(method, a0, a1, a2, rest, numArgs);
 351                 }
 352
 353                 if (pausecount > initialPauseCount) { pc++; return null; }
 354                 stack.push(ret);
 355                 break;
 356             }
 357
 358             case THROW:
 359                 throw new JSExn(stack.pop(), this);
 360
 361                 /* FIXME GRAMMAR
 362             case MAKE_GRAMMAR: {
 363                 final Grammar r = (Grammar)arg;
 364                 final JSScope final_scope = scope;
 365                 Grammar r2 = new Grammar() {
 366                         public int match(String s, int start, Hash v, JSScope scope) throws JSExn {
 367                             return r.match(s, start, v, final_scope);
 368                         }
 369                         public int matchAndWrite(String s, int start, Hash v, JSScope scope, String key) throws JSExn {
 370                             return r.matchAndWrite(s, start, v, final_scope, key);
 371                         }
 372                         public Object call(Object a0, Object a1, Object a2, Object[] rest, int nargs) throws JSExn {
 373                             Hash v = new Hash();
 374                             r.matchAndWrite((String)a0, 0, v, final_scope, "foo");
 375                             return v.get("foo");
 376                         }
 377                     };
 378                 Object obj = stack.pop();
 379                 if (obj != null && obj instanceof Grammar) r2 = new Grammar.Alternative((Grammar)obj, r2);
 380                 stack.push(r2);
 381                 break;
 382             }
 383                 */
 384             case ADD_TRAP: case DEL_TRAP: {
 385                 JS val = stack.pop();
 386                 JS key = stack.pop();
 387                 JS js = stack.peek();
 388                 // A trap addition/removal
 389                 if(!(val instanceof JSFunction)) throw new JSExn("tried to add/remove a non-function trap");
 390                 if(js instanceof JSScope) {
 391                     JSScope s = (JSScope) js;
 392                     while(s.getParentScope() != null) {
 393                         if(s.has(key)) throw new JSExn("cannot trap a variable that isn't at the top level scope");
 394                         s = s.getParentScope();
 395                     }
 396                     js = s;
 397                 }
 398                 if(op == ADD_TRAP) js.addTrap(key, (JSFunction)val);
 399                 else js.delTrap(key, (JSFunction)val);
 400                 break;
 401             }
 402
 403             case ADD: {
 404                 int count = ((JSNumber)arg).toInt();
 405                 if(count < 2) throw new Error("this should never happen");
 406                 if(count == 2) {
 407                     // common case
 408                     JS right = stack.pop();
 409                     JS left = stack.pop();
 410                     JS ret;
 411                     if(left instanceof JSString || right instanceof JSString)
 412                         ret = JS.S(JS.toString(left).concat(JS.toString(right)));
 413                     else if(left instanceof JSNumber.D || right instanceof JSNumber.D)
 414                         ret = JS.N(JS.toDouble(left) + JS.toDouble(right));
 415                     else {
 416                         long l = JS.toLong(left) + JS.toLong(right);
 417                         if(l < Integer.MIN_VALUE || l > Integer.MAX_VALUE) ret = JS.N(l);
 418                         ret = JS.N((int)l);
 419                     }
 420                     stack.push(ret);
 421                 } else {
 422                     JS[] args = new JS[count];
 423                     while(--count >= 0) args[count] = stack.pop();
 424                     if(args[0] instanceof JSString) {
 425                         StringBuffer sb = new StringBuffer(64);
 426                         for(int i=0;i<args.length;i++) sb.append(JS.toString(args[i]));
 427                         stack.push(JS.S(sb.toString()));
 428                     } else {
 429                         int numStrings = 0;
 430                         for(int i=0;i<args.length;i++) if(args[i] instanceof JSString) numStrings++;
 431                         if(numStrings == 0) {
 432                             double d = 0.0;
 433                             for(int i=0;i<args.length;i++) d += JS.toDouble(args[i]);
 434                             stack.push(JS.N(d));
 435                         } else {
 436                             int i=0;
 437                             StringBuffer sb = new StringBuffer(64);
 438                             if(!(args[0] instanceof JSString || args[1] instanceof JSString)) {
 439                                 double d=0.0;
 440                                 do {
 441                                     d += JS.toDouble(args[i++]);
 442                                 } while(!(args[i] instanceof JSString));
 443                                 sb.append(JS.toString(JS.N(d)));
 444                             }
 445                             while(i < args.length) sb.append(JS.toString(args[i++]));
 446                             stack.push(JS.S(sb.toString()));
 447                         }
 448                     }
 449                 }
 450                 break;
 451             }
 452
 453             default: {
 454                 JS right = stack.pop();
 455                 JS left = stack.pop();
 456                 switch(op) {
 457
 458                 case BITOR: stack.push(JS.N(JS.toLong(left) | JS.toLong(right))); break;
 459                 case BITXOR: stack.push(JS.N(JS.toLong(left) ^ JS.toLong(right))); break;
 460                 case BITAND: stack.push(JS.N(JS.toLong(left) & JS.toLong(right))); break;
 461
 462                 case SUB: stack.push(JS.N(JS.toDouble(left) - JS.toDouble(right))); break;
 463                 case MUL: stack.push(JS.N(JS.toDouble(left) * JS.toDouble(right))); break;
 464                 case DIV: stack.push(JS.N(JS.toDouble(left) / JS.toDouble(right))); break;
 465                 case MOD: stack.push(JS.N(JS.toDouble(left) % JS.toDouble(right))); break;
 466
 467                 case LSH: stack.push(JS.N(JS.toLong(left) << JS.toLong(right))); break;
 468                 case RSH: stack.push(JS.N(JS.toLong(left) >> JS.toLong(right))); break;
 469                 case URSH: stack.push(JS.N(JS.toLong(left) >>> JS.toLong(right))); break;
 470
 471                 //#repeat </<=/>/>= LT/LE/GT/GE
 472                 case LT: {
 473                     if(left instanceof JSString && right instanceof JSString)
 474                         stack.push(JS.B(JS.toString(left).compareTo(JS.toString(right)) < 0));
 475                     else
 476                         stack.push(JS.B(JS.toDouble(left) < JS.toDouble(right)));
 477                 }
 478                 //#end
 479
 480                 case EQ:
 481                 case NE: {
 482                     boolean ret;
 483                     if(left == null && right == null) ret = true;
 484                     else if(left == null || right == null) ret = false;
 485                     else ret = left.jsequals(right);
 486                     stack.push(JS.B(op == EQ ? ret : !ret)); break;
 487                 }
 488
 489                 default: throw new Error("unknown opcode " + op);
 490                 } }
 491             }
 492
 493         } catch(JSExn e) {
 494             catchException(e);
 495             pc--; // it'll get incremented on the next iteration
 496         } // end try/catch
 497         } // end for
 498     }
 499
 500     /** tries to find a handler withing the call chain for this exception
 501         if a handler is found the interpreter is setup to call the exception handler
 502         if a handler is not found the exception is thrown
 503     */
 504     void catchException(JSExn e) throws JSExn {
 505         while(!stack.empty()) {
 506             JS o = stack.pop();
 507             if (o instanceof CatchMarker || o instanceof TryMarker) {
 508                 boolean inCatch = o instanceof CatchMarker;
 509                 if(inCatch) {
 510                     o = stack.pop();
 511                     if(((TryMarker)o).finallyLoc < 0) continue; // no finally block, keep going
 512                 }
 513                 if(!inCatch && ((TryMarker)o).catchLoc >= 0) {
 514                     // run the catch block, this will implicitly run the finally block, if it exists
 515                     stack.push(o);
 516                     stack.push(catchMarker);
 517                     stack.push(e.getObject());
 518                     f = ((TryMarker)o).f;
 519                     scope = ((TryMarker)o).scope;
 520                     pc = ((TryMarker)o).catchLoc;
 521                     return;
 522                 } else {
 523                     stack.push(new FinallyData(e));
 524                     f = ((TryMarker)o).f;
 525                     scope = ((TryMarker)o).scope;
 526                     pc = ((TryMarker)o).finallyLoc;
 527                     return;
 528                 }
 529             }
 530         }
 531         throw e;
 532     }
 533
 534     void setupTrap(Trap t, JS val, CallMarker cm) throws JSExn {
 535         stack.push(cm);
 536         stack.push(t.isWriteTrap() ? new JSArgs(val,t.f) : new JSArgs(t.f));
 537         f = t.f;
 538         scope = new TrapScope(t.f.parentScope,t);
 539         pc = 0;
 540     }
 541
 542
 543     // Markers //////////////////////////////////////////////////////////////////////
 544
 545     static class Marker extends JS {
 546         public JS get(JS key) throws JSExn { throw new Error("this should not be accessible from a script"); }
 547         public void put(JS key, JS val) throws JSExn { throw new Error("this should not be accessible from a script"); }
 548         public String coerceToString() { throw new Error("this should not be accessible from a script"); }
 549         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"); }
 550     }
 551
 552     static class CallMarker extends Marker {
 553         final int pc;
 554         final JSScope scope;
 555         final JSFunction f;
 556         public CallMarker(Interpreter cx) {
 557             pc = cx == null ? -1 : cx.pc + 1;
 558             scope = cx == null ? null : cx.scope;
 559             f = cx == null ? null : cx.f;
 560         }
 561     }
 562
 563     static class TrapMarker extends CallMarker {
 564         Trap t;
 565         JS val;
 566         boolean cascadeHappened;
 567         final boolean pauseOnPut;
 568         public TrapMarker(Interpreter cx, Trap t, JS val) { this(cx,t,val,false); }
 569         public TrapMarker(Interpreter cx, Trap t, JS val, boolean pauseOnPut) {
 570             super(cx);
 571             this.t = t;
 572             this.val = val;
 573             this.pauseOnPut = pauseOnPut;
 574         }
 575     }
 576
 577     static class CatchMarker extends Marker { }
 578     private static CatchMarker catchMarker = new CatchMarker();
 579
 580     static class LoopMarker extends Marker {
 581         final public int location;
 582         final public String label;
 583         final public JSScope scope;
 584         public LoopMarker(int location, String label, JSScope scope) {
 585             this.location = location;
 586             this.label = label;
 587             this.scope = scope;
 588         }
 589     }
 590     static class TryMarker extends Marker {
 591         final public int catchLoc;
 592         final public int finallyLoc;
 593         final public JSScope scope;
 594         final public JSFunction f;
 595         public TryMarker(int catchLoc, int finallyLoc, Interpreter cx) {
 596             this.catchLoc = catchLoc;
 597             this.finallyLoc = finallyLoc;
 598             this.scope = cx.scope;
 599             this.f = cx.f;
 600         }
 601     }
 602     static class FinallyData extends Marker {
 603         final public int op;
 604         final public Object arg;
 605         final public JSExn exn;
 606         public FinallyData(int op) { this(op,null); }
 607         public FinallyData(int op, Object arg) { this.op = op; this.arg = arg; this.exn = null; }
 608         public FinallyData(JSExn exn) { this.exn = exn; this.op = -1; this.arg = null; } // Just throw this exn
 609     }
 610
 611     static class TrapScope extends JSScope {
 612         private Trap t;
 613         public TrapScope(JSScope parent, Trap t) {
 614             super(parent); this.t = t;
 615         }
 616         public JS get(JS key) throws JSExn {
 617             if(JS.isString(key)) {
 618                 //#switch(JS.toString(key))
 619                 case "trapee": return t.target;
 620                 case "callee": return t.f;
 621                 case "trapname": return t.key;
 622                 //#end
 623             }
 624             return super.get(key);
 625         }
 626     }
 627
 628     static class JSArgs extends JS {
 629         private final JS a0;
 630         private final JS a1;
 631         private final JS a2;
 632         private final JS[] rest;
 633         private final int nargs;
 634         private final JS callee;
 635
 636         public JSArgs(JS callee) { this(null,null,null,null,0,callee); }
 637         public JSArgs(JS a0, JS callee) { this(a0,null,null,null,1,callee); }
 638         public JSArgs(JS a0, JS a1, JS a2, JS[] rest, int nargs, JS callee) {
 639             this.a0 = a0; this.a1 = a1; this.a2 = a2;
 640             this.rest = rest; this.nargs = nargs;
 641             this.callee = callee;
 642         }
 643
 644         public JS get(JS key) throws JSExn {
 645             if(JS.isInt(key)) {
 646                 int n = JS.toInt(key);
 647                 switch(n) {
 648                     case 0: return a0;
 649                     case 1: return a1;
 650                     case 2: return a2;
 651                     default: return n>= 0 && n < nargs ? rest[n-3] : null;
 652                 }
 653             }
 654             //#switch(JS.toString(key))
 655             case "callee": return callee;
 656             case "length": return JS.N(nargs);
 657             //#end
 658             return super.get(key);
 659         }
 660     }
 661
 662     static class Stub extends JS {
 663         private JS method;
 664         JS obj;
 665         public Stub(JS obj, JS method) { this.obj = obj; this.method = method; }
 666         public JS call(JS a0, JS a1, JS a2, JS[] rest, int nargs) throws JSExn {
 667             return ((JS)obj).callMethod(method, a0, a1, a2, rest, nargs);
 668         }
 669     }
 670
 671     static class Stack {
 672         private static final int MAX_STACK_SIZE = 512;
 673         private JS[] stack = new JS[64];
 674         private int sp = 0;
 675
 676         boolean empty() { return sp == 0; }
 677         void push(JS o) throws JSExn { if(sp == stack.length) grow(); stack[sp++] = o; }
 678         JS peek() { if(sp == 0) throw new RuntimeException("Stack underflow"); return stack[sp-1]; }
 679         final JS pop() { if(sp == 0) throw new RuntimeException("Stack underflow"); return stack[--sp]; }
 680         void swap() throws JSExn {
 681             if(sp < 2) throw new JSExn("stack overflow");
 682             JS tmp = stack[sp-2];
 683             stack[sp-2] = stack[sp-1];
 684             stack[sp-1] = tmp;
 685         }
 686         CallMarker findCall() {
 687             for(int i=sp-1;i>=0;i--) if(stack[i] instanceof CallMarker) return (CallMarker) stack[i];
 688             return null;
 689         }
 690         void grow() throws JSExn {
 691             if(stack.length >= MAX_STACK_SIZE) throw new JSExn("Stack overflow");
 692             JS[] stack2 = new JS[stack.length * 2];
 693             System.arraycopy(stack,0,stack2,0,stack.length);
 694         }
 695
 696         void backtrace(JSExn e) {
 697             for(int i=sp-1;i>=0;i--) {
 698                 if (stack[i] instanceof CallMarker) {
 699                     CallMarker cm = (CallMarker)stack[i];
 700                     if(cm.f == null) break;
 701                     String s = cm.f.sourceName + ":" + cm.f.line[cm.pc-1];
 702                     if(cm instanceof Interpreter.TrapMarker)
 703                         s += " (trap on " + JS.debugToString(((Interpreter.TrapMarker)cm).t.key) + ")";
 704                     e.addBacktrace(s);
 705                 }
 706             }
 707         }
 708     }
 709 }