I was curious to see <https://man.netbsd.org/lua.4> in action, so I decided to perform some quick test.

■ printing a "hello, world!" script
First of all, load the relevant kernel modules:

$ modload lua
$ modload luasystm
  
To have them loaded automatically at boot:

printf '%s\n%s\n' 'lua' 'luasystm' >> /etc/modules.conf

If everything's right the kernel buffer will show:

 lua0: Lua 5.3.5  Copyright (C) 1994-2018 Lua.org, PUC-Rio

And `modstat` will return:

NAME                    CLASS    SOURCE   FLAG  REFS    SIZE REQUIRES 
lua                     misc     filesys  -        1       - -
luasystm                misc     filesys  -        0       - lua

Let's enhance the verbosity of the lua(4) module:

$ sysctl -w kern.lua.verbose=1
kern.lua.verbose: 0 -> 1

Without further ado, we can now proceed to test the built-in kernel parser, using  (https://man.netbsd.org/luactl.8):
1.  create a state to load our scripts
$ luactl create s1 testing
s1 created
$ luactl
Name             Creator  Description
s1               user     testing

2. load luasystm bindings on state s1 (required for print()) 
$ luactl require s1 systm
systm required by s1

3. Write a sample 'hello world' script:

$ cat << eof > hello.lua
>> -- hello world!
>> systm.print("hello world!\n")
>> eof
$ luactl load s1 ./hello.lua
./hello.lua loaded into s1
$ dmesg | tail -1
 hello world!

Notice that the absolute path is required for luactl to read the script

■ more testing
1. parsing simple functions-- sum func
function add(x, y)
  return x + y
end
systm.print("the sum of 16 and 32 is:\n")
systm.print (add(16, 32))

systm.print ("\n")

-- factorial func
function fact (n)
  if n == 0 then
    return 1
  else
    return n * fact(n-1)
  end
end
systm.print("the factorial of 7 is:\n")
systm.print (fact(7))

  

$ luactl load s1 ./sample.lua
./sample.lua loaded into s1
 $ dmesg | grep -A 5 sample
 lua0: loading ./sample.lua into state s1
 the sum of 16 and 32 is:
 48
 the factorial of 7 is:
 5040

2. displaying OS info

-- print system info
function uname()
  tbl = {"copyright", "cpu_model", "machine", "machine_arch", "osrelease", "os
type", "kernel_ident", "version"}
  for i = 1, #tbl do
    systm.print(systm] .. "\n")
  end
end

uname()

Which produces:
 lua0: loading ./sys.lua into state s1
 Copyright (c) 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005,
     2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017,
     2018, 2019, 2020 The NetBSD Foundation, Inc.  All rights reserved.
 Copyright (c) 1982, 1986, 1989, 1991, 1993
     The Regents of the University of California.  All rights reserved.

 raspberrypi,3-model-b
 evbarm
 aarch64
 9.2_STABLE
 NetBSD
 GENERIC64
 NetBSD 9.2_STABLE (GENERIC64) #0: Fri Aug 20 19:33:44 UTC 2021
 mkrepro@mkrepro.NetBSD.org:/usr/src/sys/arch/evbarm/compile/GENERIC64

3. display hostname

function hostname()
  local f = io.popen ("/bin/hostname")
  local host = f:read("*a") or ""
  f:close()
  host =string.gsub(host, "\n$", "")
  systm.print (host)
end
systm.print("Welcome to:\n")
hostname()