lparser.c

Lua 语言解释器源码

        lh->v.aux = extra;  /* previous assignment will use safe copy */
      }
    }
  }
  if (conflict) {
    luaK_codeABC(fs, OP_MOVE, fs->freereg, v->info, 0);  /* make copy */
    luaK_reserveregs(fs, 1);
  }
}


static void assignment (LexState *ls, struct LHS_assign *lh, int nvars) {
  expdesc e;
  check_condition(ls, VLOCAL <= lh->v.k && lh->v.k <= VINDEXED,
                      "syntax error");
  if (testnext(ls, ',')) {  /* assignment -> `,' primaryexp assignment */
    struct LHS_assign nv;
    nv.prev = lh;
    primaryexp(ls, &nv.v);
    if (nv.v.k == VLOCAL)
      check_conflict(ls, lh, &nv.v);
    assignment(ls, &nv, nvars+1);
  }
  else {  /* assignment -> `=' explist1 */
    int nexps;
    check(ls, '=');
    nexps = explist1(ls, &e);
    if (nexps != nvars) {
      adjust_assign(ls, nvars, nexps, &e);
      if (nexps > nvars)
        ls->fs->freereg -= nexps - nvars;  /* remove extra values */
    }
    else {
      luaK_setcallreturns(ls->fs, &e, 1);  /* close last expression */
      luaK_storevar(ls->fs, &lh->v, &e);
      return;  /* avoid default */
    }
  }
  init_exp(&e, VNONRELOC, ls->fs->freereg-1);  /* default assignment */
  luaK_storevar(ls->fs, &lh->v, &e);
}


static void cond (LexState *ls, expdesc *v) {
  /* cond -> exp */
  expr(ls, v);  /* read condition */
  if (v->k == VNIL) v->k = VFALSE;  /* `falses' are all equal here */
  luaK_goiftrue(ls->fs, v);
  luaK_patchtohere(ls->fs, v->t);
}


/*
** The while statement optimizes its code by coding the condition
** after its body (and thus avoiding one jump in the loop).
*/

/*
** maximum size of expressions for optimizing `while' code
*/
#ifndef MAXEXPWHILE
#define MAXEXPWHILE	100
#endif

/*
** the call `luaK_goiffalse' may grow the size of an expression by
** at most this:
*/
#define EXTRAEXP	5

static void whilestat (LexState *ls, int line) {
  /* whilestat -> WHILE cond DO block END */
  Instruction codeexp[MAXEXPWHILE + EXTRAEXP];
  int lineexp;
  int i;
  int sizeexp;
  FuncState *fs = ls->fs;
  int whileinit, blockinit, expinit;
  expdesc v;
  BlockCnt bl;
  next(ls);  /* skip WHILE */
  whileinit = luaK_jump(fs);  /* jump to condition (which will be moved) */
  expinit = luaK_getlabel(fs);
  expr(ls, &v);  /* parse condition */
  if (v.k == VK) v.k = VTRUE;  /* `trues' are all equal here */
  lineexp = ls->linenumber;
  luaK_goiffalse(fs, &v);
  luaK_concat(fs, &v.f, fs->jpc);
  fs->jpc = NO_JUMP;
  sizeexp = fs->pc - expinit;  /* size of expression code */
  if (sizeexp > MAXEXPWHILE) 
    luaX_syntaxerror(ls, "`while' condition too complex");
  for (i = 0; i < sizeexp; i++)  /* save `exp' code */
    codeexp[i] = fs->f->code[expinit + i];
  fs->pc = expinit;  /* remove `exp' code */
  enterblock(fs, &bl, 1);
  check(ls, TK_DO);
  blockinit = luaK_getlabel(fs);
  block(ls);
  luaK_patchtohere(fs, whileinit);  /* initial jump jumps to here */
  /* move `exp' back to code */
  if (v.t != NO_JUMP) v.t += fs->pc - expinit;
  if (v.f != NO_JUMP) v.f += fs->pc - expinit;
  for (i=0; i<sizeexp; i++)
    luaK_code(fs, codeexp[i], lineexp);
  check_match(ls, TK_END, TK_WHILE, line);
  leaveblock(fs);
  luaK_patchlist(fs, v.t, blockinit);  /* true conditions go back to loop */
  luaK_patchtohere(fs, v.f);  /* false conditions finish the loop */
}


static void repeatstat (LexState *ls, int line) {
  /* repeatstat -> REPEAT block UNTIL cond */
  FuncState *fs = ls->fs;
  int repeat_init = luaK_getlabel(fs);
  expdesc v;
  BlockCnt bl;
  enterblock(fs, &bl, 1);
  next(ls);
  block(ls);
  check_match(ls, TK_UNTIL, TK_REPEAT, line);
  cond(ls, &v);
  luaK_patchlist(fs, v.f, repeat_init);
  leaveblock(fs);
}


static int exp1 (LexState *ls) {
  expdesc e;
  int k;
  expr(ls, &e);
  k = e.k;
  luaK_exp2nextreg(ls->fs, &e);
  return k;
}


static void forbody (LexState *ls, int base, int line, int nvars, int isnum) {
  BlockCnt bl;
  FuncState *fs = ls->fs;
  int prep, endfor;
  adjustlocalvars(ls, nvars);  /* scope for all variables */
  check(ls, TK_DO);
  enterblock(fs, &bl, 1);  /* loop block */
  prep = luaK_getlabel(fs);
  block(ls);
  luaK_patchtohere(fs, prep-1);
  endfor = (isnum) ? luaK_codeAsBx(fs, OP_FORLOOP, base, NO_JUMP) :
                     luaK_codeABC(fs, OP_TFORLOOP, base, 0, nvars - 3);
  luaK_fixline(fs, line);  /* pretend that `OP_FOR' starts the loop */
  luaK_patchlist(fs, (isnum) ? endfor : luaK_jump(fs), prep);
  leaveblock(fs);
}


static void fornum (LexState *ls, TString *varname, int line) {
  /* fornum -> NAME = exp1,exp1[,exp1] DO body */
  FuncState *fs = ls->fs;
  int base = fs->freereg;
  new_localvar(ls, varname, 0);
  new_localvarstr(ls, "(for limit)", 1);
  new_localvarstr(ls, "(for step)", 2);
  check(ls, '=');
  exp1(ls);  /* initial value */
  check(ls, ',');
  exp1(ls);  /* limit */
  if (testnext(ls, ','))
    exp1(ls);  /* optional step */
  else {  /* default step = 1 */
    luaK_codeABx(fs, OP_LOADK, fs->freereg, luaK_numberK(fs, 1));
    luaK_reserveregs(fs, 1);
  }
  luaK_codeABC(fs, OP_SUB, fs->freereg - 3, fs->freereg - 3, fs->freereg - 1);
  luaK_jump(fs);
  forbody(ls, base, line, 3, 1);
}


static void forlist (LexState *ls, TString *indexname) {
  /* forlist -> NAME {,NAME} IN explist1 DO body */
  FuncState *fs = ls->fs;
  expdesc e;
  int nvars = 0;
  int line;
  int base = fs->freereg;
  new_localvarstr(ls, "(for generator)", nvars++);
  new_localvarstr(ls, "(for state)", nvars++);
  new_localvar(ls, indexname, nvars++);
  while (testnext(ls, ','))
    new_localvar(ls, str_checkname(ls), nvars++);
  check(ls, TK_IN);
  line = ls->linenumber;
  adjust_assign(ls, nvars, explist1(ls, &e), &e);
  luaK_checkstack(fs, 3);  /* extra space to call generator */
  luaK_codeAsBx(fs, OP_TFORPREP, base, NO_JUMP);
  forbody(ls, base, line, nvars, 0);
}


static void forstat (LexState *ls, int line) {
  /* forstat -> fornum | forlist */
  FuncState *fs = ls->fs;
  TString *varname;
  BlockCnt bl;
  enterblock(fs, &bl, 0);  /* block to control variable scope */
  next(ls);  /* skip `for' */
  varname = str_checkname(ls);  /* first variable name */
  switch (ls->t.token) {
    case '=': fornum(ls, varname, line); break;
    case ',': case TK_IN: forlist(ls, varname); break;
    default: luaX_syntaxerror(ls, "`=' or `in' expected");
  }
  check_match(ls, TK_END, TK_FOR, line);
  leaveblock(fs);
}


static void test_then_block (LexState *ls, expdesc *v) {
  /* test_then_block -> [IF | ELSEIF] cond THEN block */
  next(ls);  /* skip IF or ELSEIF */
  cond(ls, v);
  check(ls, TK_THEN);
  block(ls);  /* `then' part */
}


static void ifstat (LexState *ls, int line) {
  /* ifstat -> IF cond THEN block {ELSEIF cond THEN block} [ELSE block] END */
  FuncState *fs = ls->fs;
  expdesc v;
  int escapelist = NO_JUMP;
  test_then_block(ls, &v);  /* IF cond THEN block */
  while (ls->t.token == TK_ELSEIF) {
    luaK_concat(fs, &escapelist, luaK_jump(fs));
    luaK_patchtohere(fs, v.f);
    test_then_block(ls, &v);  /* ELSEIF cond THEN block */
  }
  if (ls->t.token == TK_ELSE) {
    luaK_concat(fs, &escapelist, luaK_jump(fs));
    luaK_patchtohere(fs, v.f);
    next(ls);  /* skip ELSE (after patch, for correct line info) */
    block(ls);  /* `else' part */
  }
  else
    luaK_concat(fs, &escapelist, v.f);
  luaK_patchtohere(fs, escapelist);
  check_match(ls, TK_END, TK_IF, line);
}


static void localfunc (LexState *ls) {
  expdesc v, b;
  FuncState *fs = ls->fs;
  new_localvar(ls, str_checkname(ls), 0);
  init_exp(&v, VLOCAL, fs->freereg);
  luaK_reserveregs(fs, 1);
  adjustlocalvars(ls, 1);
  body(ls, &b, 0, ls->linenumber);
  luaK_storevar(fs, &v, &b);
  /* debug information will only see the variable after this point! */
  getlocvar(fs, fs->nactvar - 1).startpc = fs->pc;
}


static void localstat (LexState *ls) {
  /* stat -> LOCAL NAME {`,' NAME} [`=' explist1] */
  int nvars = 0;
  int nexps;
  expdesc e;
  do {
    new_localvar(ls, str_checkname(ls), nvars++);
  } while (testnext(ls, ','));
  if (testnext(ls, '='))
    nexps = explist1(ls, &e);
  else {
    e.k = VVOID;
    nexps = 0;
  }
  adjust_assign(ls, nvars, nexps, &e);
  adjustlocalvars(ls, nvars);
}


static int funcname (LexState *ls, expdesc *v) {
  /* funcname -> NAME {field} [`:' NAME] */
  int needself = 0;
  singlevar(ls, v, 1);
  while (ls->t.token == '.')
    luaY_field(ls, v);
  if (ls->t.token == ':') {
    needself = 1;
    luaY_field(ls, v);
  }
  return needself;
}


static void funcstat (LexState *ls, int line) {
  /* funcstat -> FUNCTION funcname body */
  int needself;
  expdesc v, b;
  next(ls);  /* skip FUNCTION */
  needself = funcname(ls, &v);
  body(ls, &b, needself, line);
  luaK_storevar(ls->fs, &v, &b);
  luaK_fixline(ls->fs, line);  /* definition `happens' in the first line */
}


static void exprstat (LexState *ls) {
  /* stat -> func | assignment */
  FuncState *fs = ls->fs;
  struct LHS_assign v;
  primaryexp(ls, &v.v);
  if (v.v.k == VCALL) {  /* stat -> func */
    luaK_setcallreturns(fs, &v.v, 0);  /* call statement uses no results */
  }
  else {  /* stat -> assignment */
    v.prev = NULL;
    assignment(ls, &v, 1);
  }
}


static void retstat (LexState *ls) {
  /* stat -> RETURN explist */
  FuncState *fs = ls->fs;
  expdesc e;
  int first, nret;  /* registers with returned values */
  next(ls);  /* skip RETURN */
  if (block_follow(ls->t.token) || ls->t.token == ';')
    first = nret = 0;  /* return no values */
  else {
    nret = explist1(ls, &e);  /* optional return values */
    if (e.k == VCALL) {
      luaK_setcallreturns(fs, &e, LUA_MULTRET);
      if (nret == 1) {  /* tail call? */
        SET_OPCODE(getcode(fs,&e), OP_TAILCALL);
        lua_assert(GETARG_A(getcode(fs,&e)) == fs->nactvar);
      }
      first = fs->nactvar;
      nret = LUA_MULTRET;  /* return all values */
    }
    else {
      if (nret == 1)  /* only one single value? */
        first = luaK_exp2anyreg(fs, &e);
      else {
        luaK_exp2nextreg(fs, &e);  /* values must go to the `stack' */
        first = fs->nactvar;  /* return all `active' values */
        lua_assert(nret == fs->freereg - first);
      }
    }
  }
  luaK_codeABC(fs, OP_RETURN, first, nret+1, 0);
}


static void breakstat (LexState *ls) {
  /* stat -> BREAK [NAME] */
  FuncState *fs = ls->fs;
  BlockCnt *bl = fs->bl;
  int upval = 0;
  next(ls);  /* skip BREAK */
  while (bl && !bl->isbreakable) {
    upval |= bl->upval;
    bl = bl->previous;
  }
  if (!bl)
    luaX_syntaxerror(ls, "no loop to break");
  if (upval)
    luaK_codeABC(fs, OP_CLOSE, bl->nactvar, 0, 0);
  luaK_concat(fs, &bl->breaklist, luaK_jump(fs));
}


static int statement (LexState *ls) {
  int line = ls->linenumber;  /* may be needed for error messages */
  switch (ls->t.token) {
    case TK_IF: {  /* stat -> ifstat */
      ifstat(ls, line);
      return 0;
    }
    case TK_WHILE: {  /* stat -> whilestat */
      whilestat(ls, line);
      return 0;
    }
    case TK_DO: {  /* stat -> DO block END */
      next(ls);  /* skip DO */
      block(ls);
      check_match(ls, TK_END, TK_DO, line);
      return 0;
    }
    case TK_FOR: {  /* stat -> forstat */
      forstat(ls, line);
      return 0;
    }
    case TK_REPEAT: {  /* stat -> repeatstat */
      repeatstat(ls, line);
      return 0;
    }
    case TK_FUNCTION: {
      funcstat(ls, line);  /* stat -> funcstat */
      return 0;
    }
    case TK_LOCAL: {  /* stat -> localstat */
      next(ls);  /* skip LOCAL */
      if (testnext(ls, TK_FUNCTION))  /* local function? */
        localfunc(ls);
      else
        localstat(ls);
      return 0;
    }
    case TK_RETURN: {  /* stat -> retstat */
      retstat(ls);
      return 1;  /* must be last statement */
    }
    case TK_BREAK: {  /* stat -> breakstat */
      breakstat(ls);
      return 1;  /* must be last statement */
    }
    default: {
      exprstat(ls);
      return 0;  /* to avoid warnings */
    }
  }
}


static void chunk (LexState *ls) {
  /* chunk -> { stat [`;'] } */
  int islast = 0;
  enterlevel(ls);
  while (!islast && !block_follow(ls->t.token)) {
    islast = statement(ls);
    testnext(ls, ';');
    lua_assert(ls->fs->freereg >= ls->fs->nactvar);
    ls->fs->freereg = ls->fs->nactvar;  /* free registers */
  }
  leavelevel(ls);
}

/* }====================================================================== */