mnj/lua/BaseLib.java

   1 /*  $Header: //info.ravenbrook.com/project/jili/version/1.1/code/mnj/lua/BaseLib.java#1 $
   2  * Copyright (c) 2006 Nokia Corporation and/or its subsidiary(-ies).
   3  * All rights reserved.
   4  *
   5  * Permission is hereby granted, free of charge, to any person obtaining
   6  * a copy of this software and associated documentation files (the
   7  * "Software"), to deal in the Software without restriction, including
   8  * without limitation the rights to use, copy, modify, merge, publish,
   9  * distribute, sublicense, and/or sell copies of the Software, and to
  10  * permit persons to whom the Software is furnished to do so, subject
  11  * to the following conditions:
  12  *
  13  * The above copyright notice and this permission notice shall be
  14  * included in all copies or substantial portions of the Software.
  15  *
  16  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  17  * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  18  * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
  19  * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR
  20  * ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF
  21  * CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
  22  * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  23  */
  24
  25 package mnj.lua;
  26
  27 import java.io.PrintStream;
  28 import java.io.Reader;
  29 import java.util.Enumeration;
  30
  31 /**
  32  * Contains Lua's base library.  The base library is generally
  33  * considered essential for running any Lua program.  The base library
  34  * can be opened using the {@link #open} method.
  35  */
  36 public final class BaseLib extends LuaJavaCallback
  37 {
  38   // :todo: consider making the enums contiguous so that the compiler
  39   // uses the compact and faster form of switch.
  40
  41   // Each function in the base library corresponds to an instance of
  42   // this class which is associated (the 'which' member) with an integer
  43   // which is unique within this class.  They are taken from the following
  44   // set.
  45   private static final int ASSERT = 1;
  46   private static final int COLLECTGARBAGE = 2;
  47   private static final int DOFILE = 3;
  48   private static final int ERROR = 4;
  49   // private static final int GCINFO = 5;
  50   private static final int GETFENV = 6;
  51   private static final int GETMETATABLE = 7;
  52   private static final int LOADFILE = 8;
  53   private static final int LOAD = 9;
  54   private static final int LOADSTRING = 10;
  55   private static final int NEXT = 11;
  56   private static final int PCALL = 12;
  57   private static final int PRINT = 13;
  58   private static final int RAWEQUAL = 14;
  59   private static final int RAWGET = 15;
  60   private static final int RAWSET = 16;
  61   private static final int SELECT = 17;
  62   private static final int SETFENV = 18;
  63   private static final int SETMETATABLE = 19;
  64   private static final int TONUMBER = 20;
  65   private static final int TOSTRING = 21;
  66   private static final int TYPE = 22;
  67   private static final int UNPACK = 23;
  68   private static final int XPCALL = 24;
  69
  70   private static final int IPAIRS = 25;
  71   private static final int PAIRS = 26;
  72   private static final int IPAIRS_AUX = 27;
  73   private static final int PAIRS_AUX = 28;
  74
  75   // The coroutine functions (which reside in the table "coroutine") are also
  76   // part of the base library.
  77   private static final int CREATE = 50;
  78   private static final int RESUME = 51;
  79   private static final int RUNNING = 52;
  80   private static final int STATUS = 53;
  81   private static final int WRAP = 54;
  82   private static final int YIELD = 55;
  83
  84   private static final int WRAP_AUX = 56;
  85
  86   /**
  87    * Lua value that represents the generator function for ipairs.  In
  88    * PUC-Rio this is implemented as an upvalue of ipairs.
  89    */
  90   private static final Object IPAIRS_AUX_FUN = new BaseLib(IPAIRS_AUX);
  91   /**
  92    * Lua value that represents the generator function for pairs.  In
  93    * PUC-Rio this is implemented as an upvalue of pairs.
  94    */
  95   private static final Object PAIRS_AUX_FUN = new BaseLib(PAIRS_AUX);
  96
  97   /**
  98    * Which library function this object represents.  This value should
  99    * be one of the "enums" defined in the class.
 100    */
 101   private int which;
 102
 103   /**
 104    * For wrapped threads created by coroutine.wrap, this references the
 105    * Lua thread object.
 106    */
 107   private Lua thread;
 108
 109   /** Constructs instance, filling in the 'which' member. */
 110   private BaseLib(int which)
 111   {
 112     this.which = which;
 113   }
 114
 115   /** Instance constructor used by coroutine.wrap. */
 116   private BaseLib(Lua L)
 117   {
 118     this(WRAP_AUX);
 119     thread = L;
 120   }
 121
 122   /**
 123    * Implements all of the functions in the Lua base library.  Do not
 124    * call directly.
 125    * @param L  the Lua state in which to execute.
 126    * @return number of returned parameters, as per convention.
 127    */
 128   public int luaFunction(Lua L)
 129   {
 130     switch (which)
 131     {
 132       case ASSERT:
 133         return assertFunction(L);
 134       case COLLECTGARBAGE:
 135         return collectgarbage(L);
 136       case DOFILE:
 137         return dofile(L);
 138       case ERROR:
 139         return error(L);
 140       case GETFENV:
 141         return getfenv(L);
 142       case GETMETATABLE:
 143         return getmetatable(L);
 144       case IPAIRS:
 145         return ipairs(L);
 146       case LOAD:
 147         return load(L);
 148       case LOADFILE:
 149         return loadfile(L);
 150       case LOADSTRING:
 151         return loadstring(L);
 152       case NEXT:
 153         return next(L);
 154       case PAIRS:
 155         return pairs(L);
 156       case PCALL:
 157         return pcall(L);
 158       case PRINT:
 159         return print(L);
 160       case RAWEQUAL:
 161         return rawequal(L);
 162       case RAWGET:
 163         return rawget(L);
 164       case RAWSET:
 165         return rawset(L);
 166       case SELECT:
 167         return select(L);
 168       case SETFENV:
 169         return setfenv(L);
 170       case SETMETATABLE:
 171         return setmetatable(L);
 172       case TONUMBER:
 173         return tonumber(L);
 174       case TOSTRING:
 175         return tostring(L);
 176       case TYPE:
 177         return type(L);
 178       case UNPACK:
 179         return unpack(L);
 180       case XPCALL:
 181         return xpcall(L);
 182       case IPAIRS_AUX:
 183         return ipairsaux(L);
 184       case PAIRS_AUX:
 185         return pairsaux(L);
 186
 187       case CREATE:
 188         return create(L);
 189       case RESUME:
 190         return resume(L);
 191       case RUNNING:
 192         return running(L);
 193       case STATUS:
 194         return status(L);
 195       case WRAP:
 196         return wrap(L);
 197       case YIELD:
 198         return yield(L);
 199       case WRAP_AUX:
 200         return wrapaux(L);
 201     }
 202     return 0;
 203   }
 204
 205   /**
 206    * Opens the base library into the given Lua state.  This registers
 207    * the symbols of the base library in the global table.
 208    * @param L  The Lua state into which to open.
 209    */
 210   public static void open(Lua L)
 211   {
 212     // set global _G
 213     L.setGlobal("_G", L.getGlobals());
 214     // set global _VERSION
 215     L.setGlobal("_VERSION", Lua.VERSION);
 216     r(L, "assert", ASSERT);
 217     r(L, "collectgarbage", COLLECTGARBAGE);
 218     r(L, "dofile", DOFILE);
 219     r(L, "error", ERROR);
 220     r(L, "getfenv", GETFENV);
 221     r(L, "getmetatable", GETMETATABLE);
 222     r(L, "ipairs", IPAIRS);
 223     r(L, "loadfile", LOADFILE);
 224     r(L, "load", LOAD);
 225     r(L, "loadstring", LOADSTRING);
 226     r(L, "next", NEXT);
 227     r(L, "pairs", PAIRS);
 228     r(L, "pcall", PCALL);
 229     r(L, "print", PRINT);
 230     r(L, "rawequal", RAWEQUAL);
 231     r(L, "rawget", RAWGET);
 232     r(L, "rawset", RAWSET);
 233     r(L, "select", SELECT);
 234     r(L, "setfenv", SETFENV);
 235     r(L, "setmetatable", SETMETATABLE);
 236     r(L, "tonumber", TONUMBER);
 237     r(L, "tostring", TOSTRING);
 238     r(L, "type", TYPE);
 239     r(L, "unpack", UNPACK);
 240     r(L, "xpcall", XPCALL);
 241
 242     L.register("coroutine");
 243
 244     c(L, "create", CREATE);
 245     c(L, "resume", RESUME);
 246     c(L, "running", RUNNING);
 247     c(L, "status", STATUS);
 248     c(L, "wrap", WRAP);
 249     c(L, "yield", YIELD);
 250   }
 251
 252   /** Register a function. */
 253   private static void r(Lua L, String name, int which)
 254   {
 255     BaseLib f = new BaseLib(which);
 256     L.setGlobal(name, f);
 257   }
 258
 259   /** Register a function in the coroutine table. */
 260   private static void c(Lua L, String name, int which)
 261   {
 262     BaseLib f = new BaseLib(which);
 263     L.setField(L.getGlobal("coroutine"), name, f);
 264   }
 265
 266   /** Implements assert.  <code>assert</code> is a keyword in some
 267    * versions of Java, so this function has a mangled name.
 268    */
 269   private static int assertFunction(Lua L)
 270   {
 271     L.checkAny(1);
 272     if (!L.toBoolean(L.value(1)))
 273     {
 274       L.error(L.optString(2, "assertion failed!"));
 275     }
 276     return L.getTop();
 277   }
 278
 279   /** Used by {@link #collectgarbage}. */
 280   private static final String[] CGOPTS = new String[]
 281   {
 282     "stop", "restart", "collect",
 283     "count", "step", "setpause", "setstepmul"};
 284   /** Used by {@link #collectgarbage}. */
 285   private static final int[] CGOPTSNUM = new int[]
 286   {
 287     Lua.GCSTOP, Lua.GCRESTART, Lua.GCCOLLECT,
 288     Lua.GCCOUNT, Lua.GCSTEP, Lua.GCSETPAUSE, Lua.GCSETSTEPMUL};
 289   /** Implements collectgarbage. */
 290   private static int collectgarbage(Lua L)
 291   {
 292     int o = L.checkOption(1, "collect", CGOPTS);
 293     int ex = L.optInt(2, 0);
 294     int res = L.gc(CGOPTSNUM[o], ex);
 295     switch (CGOPTSNUM[o])
 296     {
 297       case Lua.GCCOUNT:
 298       {
 299         int b = L.gc(Lua.GCCOUNTB, 0);
 300         L.pushNumber(res + ((double)b)/1024);
 301         return 1;
 302       }
 303       case Lua.GCSTEP:
 304         L.pushBoolean(res != 0);
 305         return 1;
 306       default:
 307         L.pushNumber(res);
 308         return 1;
 309     }
 310   }
 311
 312   /** Implements dofile. */
 313   private static int dofile(Lua L)
 314   {
 315     String fname = L.optString(1, null);
 316     int n = L.getTop();
 317     if (L.loadFile(fname) != 0)
 318     {
 319       L.error(L.value(-1));
 320     }
 321     L.call(0, Lua.MULTRET);
 322     return L.getTop() - n;
 323   }
 324
 325   /** Implements error. */
 326   private static int error(Lua L)
 327   {
 328     int level = L.optInt(2, 1);
 329     L.setTop(1);
 330     if (Lua.isString(L.value(1)) && level > 0)
 331     {
 332       L.insert(L.where(level), 1);
 333       L.concat(2);
 334     }
 335     L.error(L.value(1));
 336     // NOTREACHED
 337     return 0;
 338   }
 339
 340   /** Helper for getfenv and setfenv. */
 341   private static Object getfunc(Lua L)
 342   {
 343     Object o = L.value(1);
 344     if (Lua.isFunction(o))
 345     {
 346       return o;
 347     }
 348     else
 349     {
 350       int level = L.optInt(1, 1);
 351       L.argCheck(level >= 0, 1, "level must be non-negative");
 352       Debug ar = L.getStack(level);
 353       if (ar == null)
 354       {
 355         L.argRaiseError(1, "invalid level");
 356       }
 357       L.getInfo("f", ar);
 358       o = L.value(-1);
 359       if (Lua.isNil(o))
 360       {
 361         L.error("no function environment for tail call at level " + level);
 362       }
 363       L.pop(1);
 364       return o;
 365     }
 366   }
 367
 368   /** Implements getfenv. */
 369   private static int getfenv(Lua L)
 370   {
 371     Object o = getfunc(L);
 372     if (Lua.isJavaFunction(o))
 373     {
 374       L.push(L.getGlobals());
 375     }
 376     else
 377     {
 378       LuaFunction f = (LuaFunction)o;
 379       L.push(f.getEnv());
 380     }
 381     return 1;
 382   }
 383
 384   /** Implements getmetatable. */
 385   private static int getmetatable(Lua L)
 386   {
 387     L.checkAny(1);
 388     Object mt = L.getMetatable(L.value(1));
 389     if (mt == null)
 390     {
 391       L.pushNil();
 392       return 1;
 393     }
 394     Object protectedmt = L.getMetafield(L.value(1), "__metatable");
 395     if (Lua.isNil(protectedmt))
 396     {
 397       L.push(mt);               // return metatable
 398     }
 399     else
 400     {
 401       L.push(protectedmt);      // return __metatable field
 402     }
 403     return 1;
 404   }
 405
 406   /** Implements load. */
 407   private static int load(Lua L)
 408   {
 409     String cname = L.optString(2, "=(load)");
 410     L.checkType(1, Lua.TFUNCTION);
 411     Reader r = new BaseLibReader(L, L.value(1));
 412     int status;
 413
 414     status = L.load(r, cname);
 415     return load_aux(L, status);
 416   }
 417
 418   /** Implements loadfile. */
 419   private static int loadfile(Lua L)
 420   {
 421     String fname = L.optString(1, null);
 422     return load_aux(L, L.loadFile(fname));
 423   }
 424
 425   /** Implements loadstring. */
 426   private static int loadstring(Lua L)
 427   {
 428     String s = L.checkString(1);
 429     String chunkname = L.optString(2, s);
 430     if (s.startsWith("\033"))
 431     {
 432       // "binary" dumped into string using string.dump.
 433       return load_aux(L, L.load(new DumpedInput(s), chunkname));
 434     }
 435     else
 436     {
 437       return load_aux(L, L.loadString(s, chunkname));
 438     }
 439   }
 440
 441   private static int load_aux(Lua L, int status)
 442   {
 443     if (status == 0)    // OK?
 444     {
 445       return 1;
 446     }
 447     else
 448     {
 449       L.insert(Lua.NIL, -1);      // put before error message
 450       return 2; // return nil plus error message
 451     }
 452   }
 453
 454   /** Implements next. */
 455   private static int next(Lua L)
 456   {
 457     L.checkType(1, Lua.TTABLE);
 458     L.setTop(2);        // Create a 2nd argument is there isn't one
 459     if (L.next(1))
 460     {
 461       return 2;
 462     }
 463     L.push(Lua.NIL);
 464     return 1;
 465   }
 466
 467   /** Implements ipairs. */
 468   private static int ipairs(Lua L)
 469   {
 470     L.checkType(1, Lua.TTABLE);
 471     L.push(IPAIRS_AUX_FUN);
 472     L.pushValue(1);
 473     L.pushNumber(0);
 474     return 3;
 475   }
 476
 477   /** Generator for ipairs. */
 478   private static int ipairsaux(Lua L)
 479   {
 480     int i = L.checkInt(2);
 481     L.checkType(1, Lua.TTABLE);
 482     ++i;
 483     Object v = Lua.rawGetI(L.value(1), i);
 484     if (Lua.isNil(v))
 485     {
 486       return 0;
 487     }
 488     L.pushNumber(i);
 489     L.push(v);
 490     return 2;
 491   }
 492
 493   /** Implements pairs.  PUC-Rio uses "next" as the generator for pairs.
 494    * Jill doesn't do that because it would be way too slow.  We use the
 495    * {@link java.util.Enumeration} returned from
 496    * {@link java.util.Hashtable#keys}.  The {@link #pairsaux} method
 497    * implements the step-by-step iteration.
 498    */
 499   private static int pairs(Lua L)
 500   {
 501     L.checkType(1, Lua.TTABLE);
 502     L.push(PAIRS_AUX_FUN);                   // return generator,
 503     LuaTable t = (LuaTable)L.value(1);
 504     L.push(new Object[] { t, t.keys() });   // state,
 505     L.push(Lua.NIL);                            // and initial value.
 506     return 3;
 507   }
 508
 509   /** Generator for pairs.  This expects a <var>state</var> and
 510    * <var>var</var> as (Lua) arguments.
 511    * The state is setup by {@link #pairs} and is a
 512    * pair of {LuaTable, Enumeration} stored in a 2-element array.  The
 513    * <var>var</var> is not used.  This is in contrast to the PUC-Rio
 514    * implementation, where the state is the table, and the var is used
 515    * to generated the next key in sequence.  The implementation, of
 516    * pairs and pairsaux, has no control over <var>var</var>,  Lua's
 517    * semantics of <code>for</code> force it to be the previous result
 518    * returned by this function.  In Jill this value is not suitable to
 519    * use for enumeration, which is why it isn't used.
 520    */
 521   private static int pairsaux(Lua L)
 522   {
 523     Object[] a = (Object[])L.value(1);
 524     LuaTable t = (LuaTable)a[0];
 525     Enumeration e = (Enumeration)a[1];
 526     if (!e.hasMoreElements())
 527     {
 528       return 0;
 529     }
 530     Object key = e.nextElement();
 531     L.push(key);
 532     L.push(t.getlua(key));
 533     return 2;
 534   }
 535
 536   /** Implements pcall. */
 537   private static int pcall(Lua L)
 538   {
 539     L.checkAny(1);
 540     int status = L.pcall(L.getTop()-1, Lua.MULTRET, null);
 541     boolean b = (status == 0);
 542     L.insert(Lua.valueOfBoolean(b), 1);
 543     return L.getTop();
 544   }
 545
 546   /**
 547    * The {@link PrintStream} used by print.  Makes it more convenient if
 548    * redirection is desired.  For example, client code could implement
 549    * their own instance which sent output to the screen of a JME device.
 550    */
 551   static final PrintStream OUT = System.out;
 552
 553   /** Implements print. */
 554   private static int print(Lua L)
 555   {
 556     int n = L.getTop();
 557     Object tostring = L.getGlobal("tostring");
 558     for(int i=1; i<=n; ++i)
 559     {
 560       L.push(tostring);
 561       L.pushValue(i);
 562       L.call(1, 1);
 563       String s = L.toString(L.value(-1));
 564       if (s == null)
 565       {
 566         return L.error("'tostring' must return a string to 'print'");
 567       }
 568       if (i>1)
 569       {
 570         OUT.print('\t');
 571       }
 572       OUT.print(s);
 573       L.pop(1);
 574     }
 575     OUT.println();
 576     return 0;
 577   }
 578
 579   /** Implements rawequal. */
 580   private static int rawequal(Lua L)
 581   {
 582     L.checkAny(1);
 583     L.checkAny(2);
 584     L.pushBoolean(Lua.rawEqual(L.value(1), L.value(2)));
 585     return 1;
 586   }
 587
 588   /** Implements rawget. */
 589   private static int rawget(Lua L)
 590   {
 591     L.checkType(1, Lua.TTABLE);
 592     L.checkAny(2);
 593     L.push(Lua.rawGet(L.value(1), L.value(2)));
 594     return 1;
 595   }
 596
 597   /** Implements rawset. */
 598   private static int rawset(Lua L)
 599   {
 600     L.checkType(1, Lua.TTABLE);
 601     L.checkAny(2);
 602     L.checkAny(3);
 603     L.rawSet(L.value(1), L.value(2), L.value(3));
 604     return 0;
 605   }
 606
 607   /** Implements select. */
 608   private static int select(Lua L)
 609   {
 610     int n = L.getTop();
 611     if (L.type(1) == Lua.TSTRING && "#".equals(L.toString(L.value(1))))
 612     {
 613       L.pushNumber(n-1);
 614       return 1;
 615     }
 616     int i = L.checkInt(1);
 617     if (i < 0)
 618     {
 619       i = n + i;
 620     }
 621     else if (i > n)
 622     {
 623       i = n;
 624     }
 625     L.argCheck(1 <= i, 1, "index out of range");
 626     return n-i;
 627   }
 628
 629   /** Implements setfenv. */
 630   private static int setfenv(Lua L)
 631   {
 632     L.checkType(2, Lua.TTABLE);
 633     Object o = getfunc(L);
 634     Object first = L.value(1);
 635     if (Lua.isNumber(first) && L.toNumber(first) == 0)
 636     {
 637       // :todo: change environment of current thread.
 638       return 0;
 639     }
 640     else if (Lua.isJavaFunction(o) || !L.setFenv(o, L.value(2)))
 641     {
 642       L.error("'setfenv' cannot change environment of given object");
 643     }
 644     L.push(o);
 645     return 1;
 646   }
 647
 648   /** Implements setmetatable. */
 649   private static int setmetatable(Lua L)
 650   {
 651     L.checkType(1, Lua.TTABLE);
 652     int t = L.type(2);
 653     L.argCheck(t == Lua.TNIL || t == Lua.TTABLE, 2,
 654         "nil or table expected");
 655     if (!Lua.isNil(L.getMetafield(L.value(1), "__metatable")))
 656     {
 657       L.error("cannot change a protected metatable");
 658     }
 659     L.setMetatable(L.value(1), L.value(2));
 660     L.setTop(1);
 661     return 1;
 662   }
 663
 664   /** Implements tonumber. */
 665   private static int tonumber(Lua L)
 666   {
 667     int base = L.optInt(2, 10);
 668     if (base == 10)     // standard conversion
 669     {
 670       L.checkAny(1);
 671       Object o = L.value(1);
 672       if (Lua.isNumber(o))
 673       {
 674         L.pushNumber(L.toNumber(o));
 675         return 1;
 676       }
 677     }
 678     else
 679     {
 680       String s = L.checkString(1);
 681       L.argCheck(2 <= base && base <= 36, 2, "base out of range");
 682       // :todo: consider stripping space and sharing some code with
 683       // Lua.vmTostring
 684       try
 685       {
 686         int i = Integer.parseInt(s, base);
 687         L.pushNumber(i);
 688         return 1;
 689       }
 690       catch (NumberFormatException e_)
 691       {
 692       }
 693     }
 694     L.push(Lua.NIL);
 695     return 1;
 696   }
 697
 698   /** Implements tostring. */
 699   private static int tostring(Lua L)
 700   {
 701     L.checkAny(1);
 702     Object o = L.value(1);
 703
 704     if (L.callMeta(1, "__tostring"))    // is there a metafield?
 705     {
 706       return 1; // use its value
 707     }
 708     switch (L.type(1))
 709     {
 710       case Lua.TNUMBER:
 711         L.push(L.toString(o));
 712         break;
 713       case Lua.TSTRING:
 714         L.push(o);
 715         break;
 716       case Lua.TBOOLEAN:
 717         if (L.toBoolean(o))
 718         {
 719           L.pushLiteral("true");
 720         }
 721         else
 722         {
 723           L.pushLiteral("false");
 724         }
 725         break;
 726       case Lua.TNIL:
 727         L.pushLiteral("nil");
 728         break;
 729       default:
 730         L.push(o.toString());
 731         break;
 732     }
 733     return 1;
 734   }
 735
 736   /** Implements type. */
 737   private static int type(Lua L)
 738   {
 739     L.checkAny(1);
 740     L.push(L.typeNameOfIndex(1));
 741     return 1;
 742   }
 743
 744   /** Implements unpack. */
 745   private static int unpack(Lua L)
 746   {
 747     L.checkType(1, Lua.TTABLE);
 748     LuaTable t = (LuaTable)L.value(1);
 749     int i = L.optInt(2, 1);
 750     int e = L.optInt(3, t.getn());
 751     int n = e - i + 1;  // number of elements
 752     if (n <= 0)
 753     {
 754       return 0;         // empty range
 755     }
 756     // i already initialised to start index, which isn't necessarily 1
 757     for (; i<=e; ++i)
 758     {
 759       L.push(t.getnum(i));
 760     }
 761     return n;
 762   }
 763
 764   /** Implements xpcall. */
 765   private static int xpcall(Lua L)
 766   {
 767     L.checkAny(2);
 768     Object errfunc = L.value(2);
 769     L.setTop(1);        // remove error function from stack
 770     int status = L.pcall(0, Lua.MULTRET, errfunc);
 771     L.insert(Lua.valueOfBoolean(status == 0), 1);
 772     return L.getTop();  // return status + all results
 773   }
 774
 775   /** Implements coroutine.create. */
 776   private static int create(Lua L)
 777   {
 778     Lua NL = L.newThread();
 779     Object faso = L.value(1);
 780     L.argCheck(Lua.isFunction(faso) && !Lua.isJavaFunction(faso), 1,
 781         "Lua function expected");
 782     L.setTop(1);        // function is at top
 783     L.xmove(NL, 1);     // move function from L to NL
 784     L.push(NL);
 785     return 1;
 786   }
 787
 788   /** Implements coroutine.resume. */
 789   private static int resume(Lua L)
 790   {
 791     Lua co = L.toThread(L.value(1));
 792     L.argCheck(co != null, 1, "coroutine expected");
 793     int r = auxresume(L, co, L.getTop() - 1);
 794     if (r < 0)
 795     {
 796       L.insert(Lua.valueOfBoolean(false), -1);
 797       return 2; // return false + error message
 798     }
 799     L.insert(Lua.valueOfBoolean(true), L.getTop()-(r-1));
 800     return r + 1;       // return true + 'resume' returns
 801   }
 802
 803   /** Implements coroutine.running. */
 804   private static int running(Lua L)
 805   {
 806     if (L.isMain())
 807     {
 808       return 0; // main thread is not a coroutine
 809     }
 810     L.push(L);
 811     return 1;
 812   }
 813
 814   /** Implements coroutine.status. */
 815   private static int status(Lua L)
 816   {
 817     Lua co = L.toThread(L.value(1));
 818     L.argCheck(co != null, 1, "coroutine expected");
 819     if (L == co)
 820     {
 821       L.pushLiteral("running");
 822     }
 823     else
 824     {
 825       switch (co.status())
 826       {
 827         case Lua.YIELD:
 828           L.pushLiteral("suspended");
 829           break;
 830         case 0:
 831           {
 832             Debug ar = co.getStack(0);
 833             if (ar != null)       // does it have frames?
 834             {
 835               L.pushLiteral("normal");    // it is running
 836             }
 837             else if (co.getTop() == 0)
 838             {
 839               L.pushLiteral("dead");
 840             }
 841             else
 842             {
 843               L.pushLiteral("suspended"); // initial state
 844             }
 845           }
 846           break;
 847         default:        // some error occured
 848           L.pushLiteral("dead");
 849       }
 850     }
 851     return 1;
 852   }
 853
 854   /** Implements coroutine.wrap. */
 855   private static int wrap(Lua L)
 856   {
 857     create(L);
 858     L.push(wrapit(L.toThread(L.value(-1))));
 859     return 1;
 860   }
 861
 862   /** Helper for wrap.  Returns a LuaJavaCallback that has access to the
 863    * Lua thread.
 864    * @param L the Lua thread to be wrapped.
 865    */
 866   private static LuaJavaCallback wrapit(Lua L)
 867   {
 868     return new BaseLib(L);
 869   }
 870
 871   /** Helper for wrap.  This implements the function returned by wrap. */
 872   private int wrapaux(Lua L)
 873   {
 874     Lua co = thread;
 875     int r = auxresume(L, co, L.getTop());
 876     if (r < 0)
 877     {
 878       if (Lua.isString(L.value(-1)))      // error object is a string?
 879       {
 880         String w = L.where(1);
 881         L.insert(w, -1);
 882         L.concat(2);
 883       }
 884       L.error(L.value(-1));     // propagate error
 885     }
 886     return r;
 887   }
 888
 889   private static int auxresume(Lua L, Lua co, int narg)
 890   {
 891     // if (!co.checkStack...
 892     if (co.status() == 0 && co.getTop() == 0)
 893     {
 894       L.pushLiteral("cannot resume dead coroutine");
 895       return -1;        // error flag;
 896     }
 897     L.xmove(co, narg);
 898     int status = co.resume(narg);
 899     if (status == 0 || status == Lua.YIELD)
 900     {
 901       int nres = co.getTop();
 902       // if (!L.checkStack...
 903       co.xmove(L, nres);        // move yielded values
 904       return nres;
 905     }
 906     co.xmove(L, 1);   // move error message
 907     return -1;        // error flag;
 908   }
 909
 910   /** Implements coroutine.yield. */
 911   private static int yield(Lua L)
 912   {
 913     return L.yield(L.getTop());
 914   }
 915 }