These functions can be called with any acceptable index.

The lua_is* functions return 1 if the object is compatible with the given type, and 0 otherwise. lua_isboolean is an exception to this rule: It succeeds only for boolean values (otherwise it would be useless, as any value has a boolean value). They always return 0 for a non-valid index. lua_isnumber accepts numbers and numerical strings; accepts strings and numbers (see ); lua_isfunction accepts both Lua functions and C functions; and lua_isuserdata accepts both full and light userdata. To distinguish between Lua functions and C functions, you can use lua_iscfunction. To distinguish between full and light userdata, you can use lua_islightuserdata. To distinguish between numbers and numerical strings, you can use lua_type.

lua_equal and lua_lessthan are equivalent to their counterparts in Lua (see 2.5.2). compares the values for primitive equality, without metamethods. These functions return 0 (false) if any of the indices are non-valid.