Ngoc M Tran

key-clash-erlang-learning

Key Clash! A typing battle game built with Erlang.

My initial plan for Seven Languages in Seven Weeks was to have a capstone weekend project for each language that showcase its essence. Coming up with such a project for each language turned out to be quite hard. It has to be small enough that a complete beginner can do it over a weekend, and interesting enough that I would want to do it specifically in that language (and not, say, constantly wishing that I’m writing a web app in Javascript). For prolog I was happy with the Zebra Puzzle. But I yearned for a more complex project.

Tada! Entered erlang and the Key Clash game.

Key Clash is like a real-time, two-player Tetris battle but for typing. Two players race through a document on separate computers, typing as fast and accurately as possible. As they progress, they build up Super Power, which can be unleashed to send a Challenge line to their opponent, making their job harder.

The project was an excellent fit for a beginner. Simple enough that I could finish a first version over a weekend. Interesting enough that I did some code refactor (gasp!) for a version 2 before running out of steam. And just complex enough that I found the excellent book Learn You Some Erlang very helpful.

Here’s a player review. 

Q: Do you like the game? 
A: Yes

Q: What do you like about it? 
A: When I get to do a super power and type silly messages. 

Q: Any features that you wish for? 
A: I feel like the score is a bit hard to see. Would be nice if it was bigger or more noticable. 

Q: Who do you want to play this game with? 
A: Grandpa. 

Q: What would you say to Grandpa when you have the super power? 
A: silllly grandpa siiiiilly grandpa

All in all, we had fun. If you play it and have suggestions, let me know! I hope that other Erlang learners might find it interesting to fork. Here’s the code with a laundry list of improvement ideas.

Erlang: the pros

I have always wondered if one can use Prolog for “normal” programming (not just solving constrained problems over finite fields). Erlang was a satisfying answer. Learning Erlang after Prolog was great. I had no troubles with the syntax, concepts, mindset. Without Prolog, I would recommend Learn You Some Erlang.

I love Erlang one-process-one-thread and let-it-crash philosophy. I like functional languages in general. I like how front-and-center the process ID is. Up until a week ago, my top three use cases for PIDs were the following.

  1. Locate the offending process that needs to be kill (90% of use cases).
  2. Nervously monitor some process that is gradually chewing up resources (more % at work, less at home)
  3. Follow some complex recipe online that says look for the PID of such-and-such service while pulling my hair out, wondering if it’s faster to handcopy that 10-page long document instead of forcing a ten-year-old printer to work on Linux. (This happens every month, about).

In short, I had an aversion for PIDs. Erlang cured that magnificently. I’m proud to have built something that can send messages across two computers. Wohoo!

Erlang: the cons

I hate the lack of an easy Erlang UI package. Initially I wanted to have a typing game that listens to keystrokes and colors the matching letters in real time. But everyone told me that Erlang + KeyListener = Horror (and I confirmed this after half a day of wrangling with wxerlang and cooked vs raw terminals). Which seems like a real, real shame. Gaming is the most exciting application to showcase concurrency imho, and few games can survive without KeyListeners.

After the initial messy implementation, I rewrote using OTP gen_server. It’s a tad cleaner, but not hugely so. I had imagined some ruby level of syntatic sugar and beauty, but nope. Probably this means I’m still an Erlang newbie and the codes could do with a lot more refactor, or that I need to add more features to appreciate the full power of the Erlang OTP.

Finally, debugging. I still find that quite confusing. We have an Arch and a Nix computer. With net_adm:ping, somehow Nix must ping Arch first, otherwise Arch cannot ping Nix, and I still cannot figure out why. Yes epmd is running on both, yes they are listening to 4369. Documentation is a bit sparse, and GPT4 (generally very good with these sorts of bugs) couldn’t help. Oh well.

Conclusion

Erlang was bult for telecom purposes, and I think it really excels at that. I would reach for Erlang as my first choice if I want to write the backend for simple network tools, manage workers, queues, chat applications, and the likes.