Lua: module 'castl.runtime' not found - lua

Question

I am new to Lua. I compiled a JS file to lua 5.2 using castl:
castl -o script.js
This created a file named script.js.lua. This is the first line of my new lua file:
local _ENV = require("castl.runtime");
I tried running that file with lua52 script.js.lua, but I got this error:
C:\Program Files\lua-5.2.4_Win64_bin\lua52.exe: script.js.lua:1: module 'castl.runtime' not found:
no field package.preload['castl.runtime']
no file 'C:\Program Files\lua-5.2.4_Win64_bin\lua\castl\runtime.lua'
no file 'C:\Program Files\lua-5.2.4_Win64_bin\lua\castl\runtime\init.lua'
no file 'C:\Program Files\lua-5.2.4_Win64_bin\castl\runtime.lua'
no file 'C:\Program Files\lua-5.2.4_Win64_bin\castl\runtime\init.lua'
no file '.\castl\runtime.lua'
no file 'C:\Program Files\lua-5.2.4_Win64_bin\castl\runtime.dll'
no file 'C:\Program Files\lua-5.2.4_Win64_bin\loadall.dll'
no file '.\castl\runtime.dll'
no file 'C:\Program Files\lua-5.2.4_Win64_bin\castl\runtime52.dll'
no file '.\castl\runtime52.dll'
no file 'C:\Program Files\lua-5.2.4_Win64_bin\castl.dll'
no file 'C:\Program Files\lua-5.2.4_Win64_bin\loadall.dll'
no file '.\castl.dll'
no file 'C:\Program Files\lua-5.2.4_Win64_bin\castl52.dll'
no file '.\castl52.dll'
stack traceback:
[C]: in function 'require'
script.js.lua:1: in main chunk
[C]: in ?
What am I missing? I am on Windows 10.

Answer 1

To answer your question
What am I missing?
Your problem is that you use a function require, but you don't know what this function does. Therefore, you cannot understand the errors it throws when it fails to do what you're expecting it to do.
So first refer to the Lua manual:
https://www.lua.org/manual/5.3/manual.html#pdf-require
There you'll find:
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 package.searchers).
and https://www.lua.org/manual/5.3/manual.html#pdf-package.path
The path used by require to search for a Lua loader.
At start-up, Lua initializes this variable with the value of the
environment variable LUA_PATH_5_3 or the environment variable LUA_PATH
or with a default path defined in luaconf.h, if those environment
variables are not defined. Any ;; in the value of the environment
variable is replaced by the default path.
For additional reading:
https://www.lua.org/pil/8.1.html
Entering "Lua require" into any web search will also result in plenty of solutions to your problem.
As hjpotter92 already stated in his comment, you have to tell your computer where to look for the files you want to require unless they are already located in the default folders.
Add the file's location to your LUA_PATH environment variable or add it to the package.path string before calling the respective require.

Answer 2

I'll leave an answer here since I believe that answer provided is actually not helping to someone who does not know anything about Lua ecosystem.
In order to require("castl.runtime") to be resolved one need to set LUA_PATH, in this case, for the sake of simplicity let's assume that castl distrib is located at /Users/me/castl, then you can:
export LUA_PATH="/Users/me/castl/lua/?.lua"
Now if you'll run Lua script it will be executed properly.