Re: Lua 5.2, setfenv and the C API

[steve donovan <steve.j.donovan@...>]

On Mon, Jan 11, 2010 at 1:42 AM, Leo Razoumov <slonik.az@gmail.com> wrote:
> Taking this statement at its face value could one simply create a
> module fenv that exports lua_getfenv/lua_setenv as Lua functions and
> get back 5.1 behavior by simply doing require "fenv" ??

Indeed!

/* Exporting getfenv/setfenv in Lua 5.2
    Note: this is basically the same code that is included if LUA_COMPAT_FENV
    is enabled (default is off)
    See lbaselib.c, search for LUA_COMPAT_FENV.
   Steve Donovan, 2010, MIT/X11
*/
#include "lua.h"
#include "lauxlib.h"
#include "lualib.h"

static void getfunc (lua_State *L, int opt) {
  if (lua_isfunction(L, 1)) lua_pushvalue(L, 1);
  else {
    lua_Debug ar;
    int level = opt ? luaL_optint(L, 1, 1) : luaL_checkint(L, 1);
    luaL_argcheck(L, level >= 0, 1, "level must be non-negative");
    if (lua_getstack(L, level, &ar) == 0)
      luaL_argerror(L, 1, "invalid level");
    lua_getinfo(L, "f", &ar);
  }
}

static int l_getfenv (lua_State *L) {
  getfunc(L, 1);
  if (lua_iscfunction(L, -1))  /* is a C function? */
    lua_pushglobaltable(L);  /* return the global env. */
  else
    lua_getfenv(L, -1);
  return 1;
}

static int l_setfenv (lua_State *L) {
  luaL_checktype(L, 2, LUA_TTABLE);
  getfunc(L, 0);
  lua_pushvalue(L, 2);
  if (lua_iscfunction(L, -2) || lua_setfenv(L, -2) == 0)
    return luaL_error(L,
             LUA_QL("setfenv") " cannot change environment of given object");
  return 1;
}

static const luaL_reg fenv[] = {
    {"getfenv",l_getfenv},
    {"setfenv",l_setfenv},
    {NULL,NULL}
};

LUALIB_API int luaopen_fenv(lua_State *L)
{
    luaL_register (L, "fenv", fenv);
    return 1;
}