new module 'auxlib' centralizes functions to get/check parameters.

auxlib.c

@@ -0,0 +1,47 @@
+char *rcs_auxlib="$Id: $";
+
+#include <stdio.h>
+
+#include "lua.h"
+
+
+void luaL_arg_check(int cond, char *funcname, int numarg, char *extramsg)
+{
+  if (!cond) {
+    char buff[100];
+    if (extramsg == NULL)
+      sprintf(buff, "bad argument #%d to function `%s'", numarg, funcname);
+    else
+      sprintf(buff, "bad argument #%d to function `%s' (%s)",
+                      numarg, funcname, extramsg);
+    lua_error(buff);
+  }
+}
+
+char *luaL_check_string (int numArg, char *funcname)
+{
+  lua_Object o = lua_getparam(numArg);
+  luaL_arg_check(lua_isstring(o), funcname, numArg, "string expected");
+  return lua_getstring(o);
+}
+
+char *luaL_opt_string (int numArg, char *def, char *funcname)
+{
+  return (lua_getparam(numArg) == LUA_NOOBJECT) ? def :
+                              luaL_check_string(numArg, funcname);
+}
+
+double luaL_check_number (int numArg, char *funcname)
+{
+  lua_Object o = lua_getparam(numArg);
+  luaL_arg_check(lua_isnumber(o), funcname, numArg, "number expected");
+  return lua_getnumber(o);
+}
+
+
+double luaL_opt_number (int numArg, double def, char *funcname)
+{
+  return (lua_getparam(numArg) == LUA_NOOBJECT) ? def :
+                              luaL_check_number(numArg, funcname);
+}
+