Question

Loads the given module.
The function starts by looking into the table package.loaded
to determine whether modname is already loaded.
If it is, then require returns the value stored
at package.loaded[modname].
Otherwise, it tries to find a loader for the module.

To find a loader,
first require queries package.preload[modname].
If it has a value,
this value (which should be a function) is the loader.
Otherwise require searches for a Lua loader using the
path stored in package.path.
If that also fails, it searches for a C loader using the
path stored in package.cpath.
If that also fails,
it tries an all-in-one loader (see below).

When loading a C library,
require first uses a dynamic link facility to link the
application with the library.
Then it tries to find a C function inside this library to
be used as the loader.
The name of this C function is the string "luaopen_"
concatenated with a copy of the module name where each dot
is replaced by an underscore.
Moreover, if the module name has a hyphen,
its prefix up to (and including) the first hyphen is removed.
For instance, if the module name is a.v1-b.c,
the function name will be luaopen_b_c.

If require finds neither a Lua library nor a
C library for a module,
it calls the all-in-one loader.
This loader searches the C path for a library for
the root name of the given module.
For instance, when requiring a.b.c,
it will search for a C library for a.
If found, it looks into it for an open function for
the submodule;
in our example, that would be luaopen_a_b_c.
With this facility, a package can pack several C submodules
into one single library,
with each submodule keeping its original open function.

Once a loader is found,
require calls the loader with a single argument, modname.
If the loader returns any value,
require assigns it to package.loaded[modname].
If the loader returns no value and
has not assigned any value to package.loaded[modname],
then require assigns true to this entry.
In any case, require returns the
final value of package.loaded[modname].

If there is any error loading or running the module,
or if it cannot find any loader for the module,
then require signals an error.