Example project for the purescript-lua

This project exists to demonstrate usage of the PureScript compiler backend for Lua.

One possible usage of Lua scripts is within the NGINX server, one can implement a backend application serving HTTP requests.

How to build / use

The project relies on nix to build dependencies.

1. Initialize nix shell:

   • Using direnv: direnv allow.
   • Using nix develop command.

2. Nix shell makes 2 executable ./scripts available on your path:

   • serve - starts Nginx and binds http://localhost:58080
   • build - compile PureScript sources to web/main.lua

3. Open one terminal for building, then execute:

$ build
Building...
PS Lua: compiling ...
Wrote linked modules to /home/yura/projects/purescript/purescript-lua/example/web/main.lua

1. Open other terminal for serving content with Nginx, run:

$ serve
NGINX: Listening on port 58080
nginx: [alert] lua_code_cache is off; this will hurt performance in web/conf/nginx.conf:13
2023/07/05 12:30:12 [notice] 1859398#1859398: using the "epoll" event method
2023/07/05 12:30:12 [notice] 1859398#1859398: openresty/1.21.4.1
2023/07/05 12:30:12 [notice] 1859398#1859398: built by gcc 12.3.0 (GCC)
2023/07/05 12:30:12 [notice] 1859398#1859398: OS: Linux 6.1.34
2023/07/05 12:30:12 [notice] 1859398#1859398: getrlimit(RLIMIT_NOFILE): 524288:524288
2023/07/05 12:30:12 [notice] 1859398#1859398: start worker processes
2023/07/05 12:30:12 [notice] 1859398#1859398: start worker process 1859399

lua_code_cache is off alert means that nginx isn't going to cache the lua script, but instead will re-read it from disk upon every HTTP request, which is exactly what we want in the development mode: it allows to re-build PS sources in the first terminal and not to restart nginx in order to see the changes.

1. Open browser and navigate to http://localhost:58080 or use httpie:

http :58080
HTTP/1.1 200 OK
Connection: keep-alive
Content-Type: text/html
Date: Tue, 16 Apr 2024 07:58:23 GMT
Server: openresty/1.21.4.3
Transfer-Encoding: chunked

Hello from "PureScript/Lua"!

How to run a compiled script

lua -e 'dofile("web/main.lua")'

but it will fail when using Nginx as there is no global variable ngx which is only defined when script is executed by nginx:

lua: web/main.lua:208: attempt to index a nil value (global 'ngx')
stack traceback:
        web/main.lua:208: in function <web/main.lua:206>
        web/main.lua:206: in main chunk
        [C]: in function 'dofile'
        (command line):1: in main chunk
        [C]: in ?