Embedding Lua in Go

I embedded lua in my leatherman so that I could add even weirder features without too much effort. It was awesome.

In order to not stress about … everything … last night I decided that a sufficiently interesting and challenging task would be to embed a lua interpreter into my leatherman, such that my discord bot that reacts to messages with emoji could easily be driven without recompilation

It was tricky; maybe the hardest part being that there are at least three major implementations of lua in Go (an abandoned Lua 5.3 VM from microsoft, a 5.2 VM from shopify, and a 5.1 VM from some rando)

I ended up selecting the 5.1 VM because the interface was slightly simpler and the error messages were good. I’d be down to use the shopify one if I could get the error messages to be more clear.

The actual change is here. I should have written it with tests etc but I didn’t feel like it. I hope this is a safe space!

I documented the API a little this evening. For the first time I am thinking that a single generated README may be a mistake.

Here’s how my older data driven api looked:

  {
    "emoji": "🇳",
    "jsonre": "^cute",
    "required": true
  },
  {
    "emoji": "🇪",
    "jsonre": "^cute",
    "required": true
  },
  {
    "emoji": "🇦",
    "jsonre": "^cute",
    "required": true
  },
  {
    "emoji": "🇹",
    "jsonre": "^cute",
    "required": true
  },

Here’s how the newer lua driven api looks:

if es:messagematches("^neat") and not es:messagematches("^neat\\s*cute") then
        es:addrequired("🇨")
        es:addrequired("🇺")
        es:addrequired("🇹")
        es:addrequired("🇪")
end

I’ve wanted to do something like this for ages. It’s not often that scripting your code is warranted, but this felt like a pretty good use-case. A non-trivial reason is that I wanted to build in more weird easter eggs without my friends being able to read the code and anticipate them.

I know for a fact that there are things I could be doing to make the code faster, like only compile the script once, rather than each time a message is received. I might do a follow up post on that if I find it interesting enough.

Hope you enjoyed this as much as me!

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Recently Brendan Gregg’s Systems Performance got its second edition released. He wrote about it here. I am hoping to get a copy myself soon. I loved the first edition and think the second will be even more useful.

At the end of 2019 I read BPF Performance Tools. It was one of my favorite tech books I read in the past five years. Not only did I learn how to (almost) trivially see deeply inside of how my computer is working, but I learned how that works via the excellent detail Gregg added in each chapter. Amazing stuff.

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