Function codeconcat

xrepo/packages/l/lua/port/lua/src/lcode.c:1640–1654

** Create code for '(e1 .. e2)'. ** For '(e1 .. e2.1 .. e2.2)' (which is '(e1 .. (e2.1 .. e2.2))', ** because concatenation is right associative), merge both CONCATs. */

** because concatenation is right associative), merge both CONCATs.
*/
static void codeconcat (FuncState *fs, expdesc *e1, expdesc *e2, int line) {
  Instruction *ie2 = previousinstruction(fs);
  if (GET_OPCODE(*ie2) == OP_CONCAT) {  /* is 'e2' a concatenation? */
    int n = GETARG_B(*ie2);  /* # of elements concatenated in 'e2' */
    lua_assert(e1->u.info + 1 == GETARG_A(*ie2));
    freeexp(fs, e2);
    SETARG_A(*ie2, e1->u.info);  /* correct first element ('e1') */
    SETARG_B(*ie2, n + 1);  /* will concatenate one more element */
  }
  else {  /* 'e2' is not a concatenation */
    luaK_codeABC(fs, OP_CONCAT, e1->u.info, 2, 0);  /* new concat opcode */
    freeexp(fs, e2);
    luaK_fixline(fs, line);
  }
}


/*