src/org/xwt/js/Interpreter.java

   1 // Copyright 2003 Adam Megacz, see the COPYING file for licensing [GPL]
   2 package org.xwt.js;
   3
   4 import org.xwt.util.*;
   5 import java.util.*;
   6 import java.io.*;
   7
   8 /** Encapsulates a single JS interpreter (ie call stack) */
   9 class Interpreter implements ByteCodes, Tokens {
  10
  11
  12     // Thread-Interpreter Mapping /////////////////////////////////////////////////////////////////////////
  13
  14     static Interpreter current() { return (Interpreter)threadToInterpreter.get(Thread.currentThread()); }
  15     private static Hashtable threadToInterpreter = new Hashtable();
  16
  17
  18     // Instance members and methods //////////////////////////////////////////////////////////////////////
  19
  20     int pausecount;               ///< the number of times pause() has been invoked; -1 indicates unpauseable
  21     JSFunction f = null;          ///< the currently-executing JSFunction
  22     JSScope scope;                ///< the current top-level scope (LIFO stack via NEWSCOPE/OLDSCOPE)
  23     Vec stack = new Vec();        ///< the object stack
  24     int pc = 0;                   ///< the program counter
  25
  26     Interpreter(JSFunction f, boolean pauseable, JSArray args) {
  27         stack.push(new Interpreter.CallMarker(this));    // the "root function returned" marker -- f==null
  28         this.f = f;
  29         this.pausecount = pauseable ? 0 : -1;
  30         this.scope = new JSScope(f.parentScope);
  31         stack.push(args);
  32     }
  33
  34     /** this is the only synchronization point we need in order to be threadsafe */
  35     synchronized Object resume() throws JSExn {
  36         Thread t = Thread.currentThread();
  37         Interpreter old = (Interpreter)threadToInterpreter.get(t);
  38         threadToInterpreter.put(t, this);
  39         try {
  40             return run();
  41         } finally {
  42             if (old == null) threadToInterpreter.remove(t);
  43             else threadToInterpreter.put(t, old);
  44         }
  45     }
  46
  47     private static JSExn je(String s) { return new JSExn(JS.getSourceName() + ":" + JS.getLine() + " " + s); }
  48
  49     // FIXME: double check the trap logic
  50     private Object run() throws JSExn {
  51
  52         // if pausecount changes after a get/put/call, we know we've been paused
  53         final int initialPauseCount = pausecount;
  54
  55         OUTER: for(;; pc++) {
  56         try {
  57             if (f == null) return stack.pop();
  58             int op = f.op[pc];
  59             Object arg = f.arg[pc];
  60             if(op == FINALLY_DONE) {
  61                 FinallyData fd = (FinallyData) stack.pop();
  62                 if(fd == null) continue OUTER; // NOP
  63                 op = fd.op;
  64                 arg = fd.arg;
  65             }
  66             switch(op) {
  67             case LITERAL: stack.push(arg); break;
  68             case OBJECT: stack.push(new JS()); break;
  69             case ARRAY: stack.push(new JSArray(JS.toNumber(arg).intValue())); break;
  70             case DECLARE: scope.declare((String)(arg==null ? stack.peek() : arg)); if(arg != null) stack.push(arg); break;
  71             case TOPSCOPE: stack.push(scope); break;
  72             case JT: if (JS.toBoolean(stack.pop())) pc += JS.toNumber(arg).intValue() - 1; break;
  73             case JF: if (!JS.toBoolean(stack.pop())) pc += JS.toNumber(arg).intValue() - 1; break;
  74             case JMP: pc += JS.toNumber(arg).intValue() - 1; break;
  75             case POP: stack.pop(); break;
  76             case SWAP: {
  77                 int depth = (arg == null ? 1 : JS.toInt(arg));
  78                 Object save = stack.elementAt(stack.size() - 1);
  79                 for(int i=stack.size() - 1; i > stack.size() - 1 - depth; i--)
  80                     stack.setElementAt(stack.elementAt(i-1), i);
  81                 stack.setElementAt(save, stack.size() - depth - 1);
  82                 break; }
  83             case DUP: stack.push(stack.peek()); break;
  84             case NEWSCOPE: scope = new JSScope(scope); break;
  85             case OLDSCOPE: scope = scope.getParentScope(); break;
  86             case ASSERT: if (!JS.toBoolean(stack.pop())) throw je("assertion failed"); break;
  87             case BITNOT: stack.push(JS.N(~JS.toLong(stack.pop()))); break;
  88             case BANG: stack.push(JS.B(!JS.toBoolean(stack.pop()))); break;
  89             case NEWFUNCTION: stack.push(((JSFunction)arg).cloneWithNewParentScope(scope)); break;
  90             case LABEL: break;
  91
  92             case TYPEOF: {
  93                 Object o = stack.pop();
  94                 if (o == null) stack.push(null);
  95                 else if (o instanceof JS) stack.push(((JS)o).typeName());
  96                 else if (o instanceof String) stack.push("string");
  97                 else if (o instanceof Number) stack.push("number");
  98                 else if (o instanceof Boolean) stack.push("boolean");
  99                 else stack.push("unknown");
 100                 break;
 101             }
 102
 103             case PUSHKEYS: {
 104                 Object o = stack.peek();
 105                 Enumeration e = ((JS)o).keys();
 106                 JSArray a = new JSArray();
 107                 while(e.hasMoreElements()) a.addElement(e.nextElement());
 108                 stack.push(a);
 109                 break;
 110             }
 111
 112             case LOOP:
 113                 stack.push(new LoopMarker(pc, pc > 0 && f.op[pc - 1] == LABEL ? (String)f.arg[pc - 1] : (String)null, scope));
 114                 stack.push(Boolean.TRUE);
 115                 break;
 116
 117             case BREAK:
 118             case CONTINUE:
 119                 while(stack.size() > 0) {
 120                     Object o = stack.pop();
 121                     if (o instanceof CallMarker) je("break or continue not within a loop");
 122                     if (o instanceof TryMarker) {
 123                         if(((TryMarker)o).finallyLoc < 0) continue; // no finally block, keep going
 124                         stack.push(new FinallyData(op, arg));
 125                         scope = ((TryMarker)o).scope;
 126                         pc = ((TryMarker)o).finallyLoc - 1;
 127                         continue OUTER;
 128                     }
 129                     if (o instanceof LoopMarker) {
 130                         if (arg == null || arg.equals(((LoopMarker)o).label)) {
 131                             int loopInstructionLocation = ((LoopMarker)o).location;
 132                             int endOfLoop = ((Integer)f.arg[loopInstructionLocation]).intValue() + loopInstructionLocation;
 133                             scope = ((LoopMarker)o).scope;
 134                             if (op == CONTINUE) { stack.push(o); stack.push(Boolean.FALSE); }
 135                             pc = op == BREAK ? endOfLoop - 1 : loopInstructionLocation;
 136                             continue OUTER;
 137                         }
 138                     }
 139                 }
 140                 throw new Error("CONTINUE/BREAK invoked but couldn't find LoopMarker at " +
 141                                 JS.getSourceName() + ":" + JS.getLine());
 142
 143             case TRY: {
 144                 int[] jmps = (int[]) arg;
 145                 // jmps[0] is how far away the catch block is, jmps[1] is how far away the finally block is
 146                 // each can be < 0 if the specified block does not exist
 147                 stack.push(new TryMarker(jmps[0] < 0 ? -1 : pc + jmps[0], jmps[1] < 0 ? -1 : pc + jmps[1], scope));
 148                 break;
 149             }
 150
 151             case RETURN: {
 152                 Object retval = stack.pop();
 153                 while(stack.size() > 0) {
 154                     Object o = stack.pop();
 155                     if (o instanceof TryMarker) {
 156                         if(((TryMarker)o).finallyLoc < 0) continue;
 157                         stack.push(retval);
 158                         stack.push(new FinallyData(RETURN));
 159                         scope = ((TryMarker)o).scope;
 160                         pc = ((TryMarker)o).finallyLoc - 1;
 161                         continue OUTER;
 162                     } else if (o instanceof CallMarker) {
 163                         if (scope instanceof Trap.TrapScope) {
 164                             Trap.TrapScope ts = (Trap.TrapScope)scope;
 165                             if (!ts.cascadeHappened) {
 166                                 ts.cascadeHappened = true;
 167                                 Trap t = ts.t.next;
 168                                 while (t != null && t.f.numFormalArgs == 0) t = t.next;
 169                                 if (t == null) {
 170                                     ((JS)ts.t.trapee).put(ts.t.name, ts.val);
 171                                     if (pausecount > initialPauseCount) { pc++; return null; }   // we were paused
 172                                 } else {
 173                                     stack.push(o);
 174                                     JSArray args = new JSArray();
 175                                     args.addElement(ts.val);
 176                                     stack.push(args);
 177                                     f = t.f;
 178                                     scope = new Trap.TrapScope(f.parentScope, t, ts.val);
 179                                     pc = -1;
 180                                     break;
 181                                 }
 182                             }
 183                         }
 184                         scope = ((CallMarker)o).scope;
 185                         pc = ((CallMarker)o).pc - 1;
 186                         f = (JSFunction)((CallMarker)o).f;
 187                         stack.push(retval);
 188                         continue OUTER;
 189                     }
 190                 }
 191                 throw new Error("error: RETURN invoked but couldn't find a CallMarker!");
 192             }
 193
 194             case PUT: {
 195                 Object val = stack.pop();
 196                 Object key = stack.pop();
 197                 Object target = stack.peek();
 198                 if (target == null)
 199                     throw je("tried to put a value to the " + key + " property on the null value");
 200                 if (!(target instanceof JS))
 201                     throw je("tried to put a value to the " + key + " property on a " + target.getClass().getName());
 202                 if (key == null)
 203                     throw je("tried to assign \"" + (val==null?"(null)":val.toString()) + "\" to the null key");
 204                 Trap t = null;
 205                 if (target instanceof JS) {
 206                     t = ((JS)target).getTrap(key);
 207                     while (t != null && t.f.numFormalArgs == 0) t = t.next;
 208                 } else if (target instanceof Trap.TrapScope && key.equals("cascade")) {
 209                     Trap.TrapScope ts = (Trap.TrapScope)target;
 210                     t = ts.t.next;
 211                     ts.cascadeHappened = true;
 212                     while (t != null && t.f.numFormalArgs == 0) t = t.next;
 213                     if (t == null) target = ts.t.trapee;
 214                 }
 215                 if (t != null) {
 216                     stack.push(new CallMarker(this));
 217                     JSArray args = new JSArray();
 218                     args.addElement(val);
 219                     stack.push(args);
 220                     f = t.f;
 221                     scope = new Trap.TrapScope(f.parentScope, t, val);
 222                     pc = -1;
 223                     break;
 224                 }
 225                 ((JS)target).put(key, val);
 226                 if (pausecount > initialPauseCount) { pc++; return null; }   // we were paused
 227                 stack.push(val);
 228                 break;
 229             }
 230
 231             case GET:
 232             case GET_PRESERVE: {
 233                 Object o, v;
 234                 if (op == GET) {
 235                     v = arg == null ? stack.pop() : arg;
 236                     o = stack.pop();
 237                 } else {
 238                     v = stack.pop();
 239                     o = stack.peek();
 240                     stack.push(v);
 241                 }
 242                 Object ret = null;
 243                 if (v == null) throw je("tried to get the null key from " + o);
 244                 if (o == null) throw je("tried to get property \"" + v + "\" from the null object");
 245                 if (o instanceof String || o instanceof Number || o instanceof Boolean) {
 246                     ret = getFromPrimitive(o,v);
 247                     stack.push(ret);
 248                     break;
 249                 } else if (o instanceof JS) {
 250                     Trap t = null;
 251                     if (o instanceof JS) {
 252                         t = ((JS)o).getTrap(v);
 253                         while (t != null && t.f.numFormalArgs != 0) t = t.next;
 254                     } else if (o instanceof Trap.TrapScope && v.equals("cascade")) {
 255                         t = ((Trap.TrapScope)o).t.next;
 256                         while (t != null && t.f.numFormalArgs != 0) t = t.next;
 257                         if (t == null) o = ((Trap.TrapScope)o).t.trapee;
 258                     }
 259                     if (t != null) {
 260                         stack.push(new CallMarker(this));
 261                         JSArray args = new JSArray();
 262                         stack.push(args);
 263                         f = t.f;
 264                         scope = new Trap.TrapScope(f.parentScope, t, null);
 265                         ((Trap.TrapScope)scope).cascadeHappened = true;
 266                         pc = -1;
 267                         break;
 268                     }
 269                     ret = ((JS)o).get(v);
 270                     if (ret == JS.METHOD) ret = new Stub((JS)o, v);
 271                     if (pausecount > initialPauseCount) { pc++; return null; }   // we were paused
 272                     stack.push(ret);
 273                     break;
 274                 }
 275                 throw je("tried to get property " + v + " from a " + o.getClass().getName());
 276             }
 277
 278             case CALL: case CALLMETHOD: {
 279                 int numArgs = JS.toInt(arg);
 280                 Object method = null;
 281                 Object ret = null;
 282                 Object object = stack.pop();
 283
 284                 if (op == CALLMETHOD) {
 285                     if (object == JS.METHOD) {
 286                         method = stack.pop();
 287                         object = stack.pop();
 288                     } else if (object == null) {
 289                         Object name = stack.pop();
 290                         stack.pop();
 291                         throw new JSExn("function '"+name+"' not found");
 292                     } else {
 293                         stack.pop();
 294                         stack.pop();
 295                     }
 296                 }
 297                 Object[] rest = numArgs > 3 ? new Object[numArgs - 3] : null;
 298                 for(int i=numArgs - 1; i>2; i--) rest[i-3] = stack.pop();
 299                 Object a2 = numArgs <= 2 ? null : stack.pop();
 300                 Object a1 = numArgs <= 1 ? null : stack.pop();
 301                 Object a0 = numArgs <= 0 ? null : stack.pop();
 302
 303                 if (object instanceof String || object instanceof Number || object instanceof Boolean) {
 304                     ret = callMethodOnPrimitive(object, method, a0, a1, a2, null, numArgs);
 305
 306                 } else if (object instanceof JSFunction) {
 307                     // FIXME: use something similar to call0/call1/call2 here
 308                     JSArray arguments = new JSArray();
 309                     for(int i=0; i<numArgs; i++) arguments.addElement(i==0?a0:i==1?a1:i==2?a2:rest[i-3]);
 310                     stack.push(new CallMarker(this));
 311                     stack.push(arguments);
 312                     f = (JSFunction)object;
 313                     scope = new JSScope(f.parentScope);
 314                     pc = -1;
 315                     break;
 316
 317                 } else if (object instanceof JS) {
 318                     JS c = (JS)object;
 319                     ret = method == null ? c.call(a0, a1, a2, rest, numArgs) : c.callMethod(method, a0, a1, a2, rest, numArgs);
 320
 321                 } else {
 322                     throw new JSExn("can't call a " + object + " @" + pc + "\n" + f.dump());
 323
 324                 }
 325                 if (pausecount > initialPauseCount) { pc++; return null; }
 326                 stack.push(ret);
 327                 break;
 328             }
 329
 330             case THROW: {
 331                 Object o = stack.pop();
 332                 if(o instanceof JSExn) throw (JSExn)o;
 333                 throw new JSExn(o);
 334             }
 335
 336             case ASSIGN_SUB: case ASSIGN_ADD: {
 337                 Object val = stack.pop();
 338                 Object old = stack.pop();
 339                 Object key = stack.pop();
 340                 Object obj = stack.peek();
 341                 if (val instanceof JSFunction && obj instanceof JSScope) {
 342                     JSScope parent = (JSScope)obj;
 343                     while(parent.getParentScope() != null) parent = parent.getParentScope();
 344                     if (parent instanceof JS) {
 345                         JS b = (JS)parent;
 346                         if (op == ASSIGN_ADD) b.addTrap(key, (JSFunction)val);
 347                         else b.delTrap(key, (JSFunction)val);
 348                         // skip over the "normal" implementation of +=/-=
 349                         pc += ((Integer)arg).intValue() - 1;
 350                         break;
 351                     }
 352                 }
 353                 // use the "normal" implementation
 354                 stack.push(key);
 355                 stack.push(old);
 356                 stack.push(val);
 357                 break;
 358             }
 359
 360             case ADD: {
 361                 int count = ((Number)arg).intValue();
 362                 if(count < 2) throw new Error("this should never happen");
 363                 if(count == 2) {
 364                     // common case
 365                     Object right = stack.pop();
 366                     Object left = stack.pop();
 367                     if(left instanceof String || right instanceof String)
 368                         stack.push(JS.toString(left).concat(JS.toString(right)));
 369                     else stack.push(JS.N(JS.toDouble(left) + JS.toDouble(right)));
 370                 } else {
 371                     Object[] args = new Object[count];
 372                     while(--count >= 0) args[count] = stack.pop();
 373                     if(args[0] instanceof String) {
 374                         StringBuffer sb = new StringBuffer(64);
 375                         for(int i=0;i<args.length;i++) sb.append(JS.toString(args[i]));
 376                         stack.push(sb.toString());
 377                     } else {
 378                         int numStrings = 0;
 379                         for(int i=0;i<args.length;i++) if(args[i] instanceof String) numStrings++;
 380                         if(numStrings == 0) {
 381                             double d = 0.0;
 382                             for(int i=0;i<args.length;i++) d += JS.toDouble(args[i]);
 383                             stack.push(JS.N(d));
 384                         } else {
 385                             int i=0;
 386                             StringBuffer sb = new StringBuffer(64);
 387                             if(!(args[0] instanceof String || args[1] instanceof String)) {
 388                                 double d=0.0;
 389                                 do {
 390                                     d += JS.toDouble(args[i++]);
 391                                 } while(!(args[i] instanceof String));
 392                                 sb.append(JS.toString(JS.N(d)));
 393                             }
 394                             while(i < args.length) sb.append(JS.toString(args[i++]));
 395                             stack.push(sb.toString());
 396                         }
 397                     }
 398                 }
 399                 break;
 400             }
 401
 402             default: {
 403                 Object right = stack.pop();
 404                 Object left = stack.pop();
 405                 switch(op) {
 406
 407                 case BITOR: stack.push(JS.N(JS.toLong(left) | JS.toLong(right))); break;
 408                 case BITXOR: stack.push(JS.N(JS.toLong(left) ^ JS.toLong(right))); break;
 409                 case BITAND: stack.push(JS.N(JS.toLong(left) & JS.toLong(right))); break;
 410
 411                 case SUB: stack.push(JS.N(JS.toDouble(left) - JS.toDouble(right))); break;
 412                 case MUL: stack.push(JS.N(JS.toDouble(left) * JS.toDouble(right))); break;
 413                 case DIV: stack.push(JS.N(JS.toDouble(left) / JS.toDouble(right))); break;
 414                 case MOD: stack.push(JS.N(JS.toDouble(left) % JS.toDouble(right))); break;
 415
 416                 case LSH: stack.push(JS.N(JS.toLong(left) << JS.toLong(right))); break;
 417                 case RSH: stack.push(JS.N(JS.toLong(left) >> JS.toLong(right))); break;
 418                 case URSH: stack.push(JS.N(JS.toLong(left) >>> JS.toLong(right))); break;
 419
 420                 case LT: case LE: case GT: case GE: {
 421                     if (left == null) left = JS.N(0);
 422                     if (right == null) right = JS.N(0);
 423                     int result = 0;
 424                     if (left instanceof String || right instanceof String) {
 425                         result = left.toString().compareTo(right.toString());
 426                     } else {
 427                         result = (int)java.lang.Math.ceil(JS.toDouble(left) - JS.toDouble(right));
 428                     }
 429                     stack.push(JS.B((op == LT && result < 0) || (op == LE && result <= 0) ||
 430                                (op == GT && result > 0) || (op == GE && result >= 0)));
 431                     break;
 432                 }
 433
 434                 case EQ:
 435                 case NE: {
 436                     Object l = left;
 437                     Object r = right;
 438                     boolean ret;
 439                     if (l == null) { Object tmp = r; r = l; l = tmp; }
 440                     if (l == null && r == null) ret = true;
 441                     else if (r == null) ret = false; // l != null, so its false
 442                     else if (l instanceof Boolean) ret = JS.B(JS.toBoolean(r)).equals(l);
 443                     else if (l instanceof Number) ret = JS.toNumber(r).doubleValue() == JS.toNumber(l).doubleValue();
 444                     else if (l instanceof String) ret = r != null && l.equals(r.toString());
 445                     else ret = l.equals(r);
 446                     stack.push(JS.B(op == EQ ? ret : !ret)); break;
 447                 }
 448
 449                 default: throw new Error("unknown opcode " + op);
 450                 } }
 451             }
 452
 453         } catch(JSExn e) {
 454             while(stack.size() > 0) {
 455                 Object o = stack.pop();
 456                 if (o instanceof CatchMarker || o instanceof TryMarker) {
 457                     boolean inCatch = o instanceof CatchMarker;
 458                     if(inCatch) {
 459                         o = stack.pop();
 460                         if(((TryMarker)o).finallyLoc < 0) continue; // no finally block, keep going
 461                     }
 462                     if(!inCatch && ((TryMarker)o).catchLoc >= 0) {
 463                         // run the catch block, this will implicitly run the finally block, if it exists
 464                         stack.push(o);
 465                         stack.push(catchMarker);
 466                         stack.push(e.getObject());
 467                         scope = ((TryMarker)o).scope;
 468                         pc = ((TryMarker)o).catchLoc - 1;
 469                         continue OUTER;
 470                     } else {
 471                         stack.push(e);
 472                         stack.push(new FinallyData(THROW));
 473                         scope = ((TryMarker)o).scope;
 474                         pc = ((TryMarker)o).finallyLoc - 1;
 475                         continue OUTER;
 476                     }
 477                 }
 478                 // no handler found within this func
 479                 if(o instanceof CallMarker) throw e;
 480             }
 481             throw e;
 482         } // end try/catch
 483         } // end for
 484     }
 485
 486
 487
 488     // Markers //////////////////////////////////////////////////////////////////////
 489
 490     public static class CallMarker {
 491         int pc;
 492         JSScope scope;
 493         JSFunction f;
 494         public CallMarker(Interpreter cx) { pc = cx.pc + 1; scope = cx.scope; f = cx.f; }
 495     }
 496
 497     public static class CatchMarker { public CatchMarker() { } }
 498     private static CatchMarker catchMarker = new CatchMarker();
 499
 500     public static class LoopMarker {
 501         public int location;
 502         public String label;
 503         public JSScope scope;
 504         public LoopMarker(int location, String label, JSScope scope) {
 505             this.location = location;
 506             this.label = label;
 507             this.scope = scope;
 508         }
 509     }
 510     public static class TryMarker {
 511         public int catchLoc;
 512         public int finallyLoc;
 513         public JSScope scope;
 514         public TryMarker(int catchLoc, int finallyLoc, JSScope scope) {
 515             this.catchLoc = catchLoc;
 516             this.finallyLoc = finallyLoc;
 517             this.scope = scope;
 518         }
 519     }
 520     public static class FinallyData {
 521         public int op;
 522         public Object arg;
 523         public FinallyData(int op, Object arg) { this.op = op; this.arg = arg; }
 524         public FinallyData(int op) { this(op,null); }
 525     }
 526
 527
 528     // Operations on Primitives //////////////////////////////////////////////////////////////////////
 529
 530     static Object callMethodOnPrimitive(Object o, Object method, Object arg0, Object arg1, Object arg2, Object[] rest, int alength) throws JSExn {
 531         if (o instanceof Number) {
 532             //#switch(method)
 533             case "toFixed": throw new JSExn("toFixed() not implemented");
 534             case "toExponential": throw new JSExn("toExponential() not implemented");
 535             case "toPrecision": throw new JSExn("toPrecision() not implemented");
 536             case "toString": {
 537                 int radix = alength >= 1 ? JS.toInt(arg0) : 10;
 538                 return Long.toString(((Number)o).longValue(),radix);
 539             }
 540             //#end
 541         } else if (o instanceof Boolean) {
 542             // No methods for Booleans
 543             throw new JSExn("attempt to call a method on a Boolean");
 544         }
 545
 546         String s = JS.toString(o);
 547         int slength = s.length();
 548         //#switch(method)
 549         case "substring": {
 550             int a = alength >= 1 ? JS.toInt(arg0) : 0;
 551             int b = alength >= 2 ? JS.toInt(arg1) : slength;
 552             if (a > slength) a = slength;
 553             if (b > slength) b = slength;
 554             if (a < 0) a = 0;
 555             if (b < 0) b = 0;
 556             if (a > b) { int tmp = a; a = b; b = tmp; }
 557             return s.substring(a,b);
 558         }
 559         case "substr": {
 560             int start = alength >= 1 ? JS.toInt(arg0) : 0;
 561             int len = alength >= 2 ? JS.toInt(arg1) : Integer.MAX_VALUE;
 562             if (start < 0) start = slength + start;
 563             if (start < 0) start = 0;
 564             if (len < 0) len = 0;
 565             if (len > slength - start) len = slength - start;
 566             if (len <= 0) return "";
 567             return s.substring(start,start+len);
 568         }
 569         case "charAt": {
 570             int p = alength >= 1 ? JS.toInt(arg0) : 0;
 571             if (p < 0 || p >= slength) return "";
 572             return s.substring(p,p+1);
 573         }
 574         case "charCodeAt": {
 575             int p = alength >= 1 ? JS.toInt(arg0) : 0;
 576             if (p < 0 || p >= slength) return JS.N(Double.NaN);
 577             return JS.N(s.charAt(p));
 578         }
 579         case "concat": {
 580             StringBuffer sb = new StringBuffer(slength*2).append(s);
 581             for(int i=0;i<alength;i++) sb.append(i==0?arg0:i==1?arg1:i==2?arg2:rest[i-3]);
 582             return sb.toString();
 583         }
 584         case "indexOf": {
 585             String search = alength >= 1 ? arg0.toString() : "null";
 586             int start = alength >= 2 ? JS.toInt(arg1) : 0;
 587             // Java's indexOf handles an out of bounds start index, it'll return -1
 588             return JS.N(s.indexOf(search,start));
 589         }
 590         case "lastIndexOf": {
 591             String search = alength >= 1 ? arg0.toString() : "null";
 592             int start = alength >= 2 ? JS.toInt(arg1) : 0;
 593             // Java's indexOf handles an out of bounds start index, it'll return -1
 594             return JS.N(s.lastIndexOf(search,start));
 595         }
 596         case "match": return JSRegexp.stringMatch(s,arg0);
 597         case "replace": return JSRegexp.stringReplace(s,(String)arg0,arg1);
 598         case "search": return JSRegexp.stringSearch(s,arg0);
 599         case "split": return JSRegexp.stringSplit(s,arg0,arg1,alength);
 600         case "toLowerCase": return s.toLowerCase();
 601         case "toUpperCase": return s.toUpperCase();
 602         case "toString": return s;
 603         case "slice": {
 604             int a = alength >= 1 ? JS.toInt(arg0) : 0;
 605             int b = alength >= 2 ? JS.toInt(arg1) : slength;
 606             if (a < 0) a = slength + a;
 607             if (b < 0) b = slength + b;
 608             if (a < 0) a = 0;
 609             if (b < 0) b = 0;
 610             if (a > slength) a = slength;
 611             if (b > slength) b = slength;
 612             if (a > b) return "";
 613             return s.substring(a,b);
 614         }
 615         //#end
 616         throw new JSExn("Attempted to call non-existent method: " + method);
 617     }
 618
 619     static Object getFromPrimitive(Object o, Object key) throws JSExn {
 620         boolean returnJS = false;
 621         if (o instanceof Boolean) {
 622             throw new JSExn("cannot call methods on Booleans");
 623         } else if (o instanceof Number) {
 624             if (key.equals("toPrecision") || key.equals("toExponential") || key.equals("toFixed"))
 625                 returnJS = true;
 626         }
 627         if (!returnJS) {
 628             // the string stuff applies to everything
 629             String s = o.toString();
 630
 631             // this is sort of ugly, but this list should never change
 632             // These should provide a complete (enough) implementation of the ECMA-262 String object
 633
 634             //#switch(key)
 635             case "length": return JS.N(s.length());
 636             case "substring": returnJS = true; break;
 637             case "charAt": returnJS = true; break;
 638             case "charCodeAt": returnJS = true; break;
 639             case "concat": returnJS = true; break;
 640             case "indexOf": returnJS = true; break;
 641             case "lastIndexOf": returnJS = true; break;
 642             case "match": returnJS = true; break;
 643             case "replace": returnJS = true; break;
 644             case "seatch": returnJS = true; break;
 645             case "slice": returnJS = true; break;
 646             case "split": returnJS = true; break;
 647             case "toLowerCase": returnJS = true; break;
 648             case "toUpperCase": returnJS = true; break;
 649             case "toString": returnJS = true; break;
 650             case "substr": returnJS = true; break;
 651            //#end
 652         }
 653         if (returnJS) {
 654             final Object target = o;
 655             final String method = key.toString();
 656             return new JS() {
 657                     public Object call(Object a0, Object a1, Object a2, Object[] rest, int nargs) throws JSExn {
 658                         if (nargs > 2) throw new JSExn("cannot call that method with that many arguments");
 659                         return callMethodOnPrimitive(target, method, a0, a1, a2, rest, nargs);
 660                     }
 661             };
 662         }
 663         return null;
 664     }
 665
 666     private static class Stub extends JS {
 667         private Object method;
 668         JS obj;
 669         public Stub(JS obj, Object method) { this.obj = obj; this.method = method; }
 670         public Object call(Object a0, Object a1, Object a2, Object[] rest, int nargs) throws JSExn {
 671             return ((JS)obj).callMethod(method, a0, a1, a2, rest, nargs);
 672         }
 673     }
 674 }