Re: cons cells for Lua

[Roberto Ierusalimschy <roberto@...>]

To add more fun to the discussion, follows a small C module that adds
tuples to Lua. In some quick tests, they outperform tables both in
space and creation time, but are slower to access.

Manual:

  a = newtuple(v1, v2, ..., vn)   -- creates a new tuple
  a(i)   --> returns vi
  a()    --> returns v1, v2, ... vn

-- Roberto


#include <lua.h>
#include <lauxlib.h>



static int tuple_access (lua_State *L) {
  int a = luaL_optint(L, 1, 0);
  if (a == 0) {  /* returns all elements? */
    int i;
    for (i=1; lua_type(L, lua_upvalueindex(i)) != LUA_TNONE; i++)
      lua_pushvalue(L, lua_upvalueindex(i));
    return i-1;
  }
  else {
    luaL_argcheck(L, 1 <= a && lua_type(L, lua_upvalueindex(a)) != LUA_TNONE,
                     1, "invalid index");
    lua_pushvalue(L, lua_upvalueindex(a));
    return 1;
  }
}


static int tuple_new (lua_State *L) {
  int n = lua_gettop(L);
  luaL_argcheck(L, n <= LUA_MINSTACK, n, "too many fields");
  lua_pushcclosure(L, tuple_access, n);
  return 1;
}


int luaopen_tuple (lua_State *L) {
  lua_register(L, "newtuple", tuple_new);
  return 0;
}