Re: Behavior of logical operators

[Gavin Wraith <gavin@...>]

In message <AANLkTinA5F+hOtmWB+qD+vWSt-UYN4ScadytB3R=q3A4@mail.gmail.com> you wrote:

> 2011/3/13 Axel Kittenberger <axkibe@gmail.com>
>
> > > I would expect this expression to return "true". What am I missing?
> >
> > This is a known bug. See http://www.lua.org/bugs.html#5.1.4-3
> >
> > Personally I consider this a very grave bug if basic operations go
> > wrong, and its been a year. When can we expect an official version
> > with logical operators fixed?
> >
> > and it happens in lua5.2-alpha, too.

I use lua5.2-alpha with the following patch (marked by
#if 0 ... #endif) in lcode.c which seems to cure the problem:

/ ---- begin code -------
void luaK_goiftrue (FuncState *fs, expdesc *e) {
  int pc;  /* pc of last jump */
  luaK_dischargevars(fs, e);
  switch (e->k) {
#if 0
      case VK: case VKNUM: case VTRUE: {
      pc = NO_JUMP;  /* always true; do nothing */
      break;
    }
#endif
    case VJMP: {
      invertjump(fs, e);
      pc = e->u.info;
      break;
    }
#if 0
    case VFALSE: {
      if (!hasjumps(e)) {
        pc = luaK_jump(fs);  /* always jump */
        break;
      }
      /* else go through */
    }
#endif
    default: {
      pc = jumponcond(fs, e, 0);
      break;
    }
  }
  luaK_concat(fs, &e->f, pc);  /* insert last jump in `f' list */
  luaK_patchtohere(fs, e->t);
  e->t = NO_JUMP;
}


static void luaK_goiffalse (FuncState *fs, expdesc *e) {
  int pc;  /* pc of last jump */
  luaK_dischargevars(fs, e);
  switch (e->k) {
#if 0
    case VNIL: case VFALSE: {
      pc = NO_JUMP;  /* always false; do nothing */
      break;
    }
#endif
    case VJMP: {
      pc = e->u.info;
      break;
    }
#if 0
    case VTRUE: {
      if (!hasjumps(e)) {
        pc = luaK_jump(fs);  /* always jump */
        break;
      }
      /* else go through */
    }
#endif
    default: {
      pc = jumponcond(fs, e, 1);
      break;
    }
  }
  luaK_concat(fs, &e->t, pc);  /* insert last jump in `t' list */
  luaK_patchtohere(fs, e->f);
  e->f = NO_JUMP;
}
/ ------- end code --------

-- 
Gavin Wraith (gavin@wra1th.plus.com)
Home page: http://www.wra1th.plus.com/