Small enhancement for os lib, Was: re: libext

[Rici Lake <lua@...>]

On 5-Aug-04, at 1:03 PM, Alex Sandro Queiroz e Silva wrote:

>    Similarly, when you read the Lua Manual you know that everything 
> there holds for every ANSI C-compliant platform. There is no need to 
> test for anything. But if you need os.ext.delay, you know you must 
> test if it exists because of the "ext" in the name. In the end, I 
> think the clarity of the name pays off.

Not really. For example, the ANSI C library does not insist that
system() do anything other than return an error message, but
it provides a way for the caller to determine whether there is
any string which would work: (see second sentence)

> int system(const char *s);
>
> If s is not a null pointer, the function passes the string  s to be
> executed by a command processor, supplied by the target environment,
> and returns the status reported by the command processor. If s is a
> null pointer, the function returns nonzero only if the target
> environment supplies a command processor. Each implementation defines
> what strings its command processor accepts.

Unfortunately, the current implementation of os.execute does not reflect
this definition very well; there is no way to do the indicated test.

Similarly, ANSI C does not presuppose that the machine actually has any
notion of the current time: "The function returns the current calendar 
time, if the target environment can determine it; otherwise, it returns 
-1."

Lua's os.time() simply hands this error value back to the caller,
although it tests for the error code in the case where mktime()
is called.

Possible changes:

Current implementation:

static int io_execute (lua_State *L) {
  lua_pushnumber(L, system(luaL_checkstring(L, 1)));
  return 1;
}

Replace with some variation on:

static int io_execute (lua_State *L) {
  const char *cmd = NULL;
  int status;
  if (!lua_isnoneornil(L, 1)) cmd = luaL_checkstring(L, 1);
  system(cmd);
  lua_pushboolean(L, status == 0);
  lua_pushnumber(L, (lua_Number)status);
  return 2;
}

and:

static int io_time (lua_State *L) {
  if (lua_isnoneornil(L, 1))  /* called without args? */
    lua_pushnumber(L, time(NULL));  /* return current time */
  else {
    time_t t;
/* SNIP */
    t = mktime(&ts);
    if (t == (time_t)(-1))
      lua_pushnil(L);
    else
      lua_pushnumber(L, t);
  }
  return 1;
}

Replace with:

static int io_time (lua_State *L) {
  time_t t;
  if (lua_isnoneornil(L, 1))  /* called without args? */
    t = time(NULL);  /* return current time */
  else {
/* SNIP */
    t = mktime(&ts);
  }
  if (t == (time_t)(-1))
    lua_pushnil(L);
  else
    lua_pushnumber(L, t);
  return 1;
}

Sorry about not providing real patch files :(

Rici