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150k lines of vibe coded Elixir: The good, the bad and the ugly
- logicprog 8mo agoIt's interesting that Claude is able to effectively write Elixir, even if it isn't super idiomatic without established styles in the codebase, considering Elixir is a pretty niche and relatively recent language. What I'd really like to see though is experiments on whether you can few shot prompt an AI to in-context-learn a new language with any level of success.
- ch4s3 8mo agoYou can accurately describe elixir syntax in a few paragraphs, and the semantics are pretty straightforward. I’d imagine doing complex supervision trees falls flat.
- dist-epoch 8mo agoUnless that new language has truly esoteric concepts, it's trivial to pattern-match it to regular programming constructs (loops, functions, ...)
- d3ckard 8mo agoI would argue effectiveness point. It's certainly helpful, but has a tendency to go for very non idiomatic patterns (like using exceptions for control flow). Plus, it has issues which I assume are the effect of reinforcement learning - it struggles with letting things crash and tends to silence things that should never fail silently.
- troupo 8mo ago> has a tendency to go for very non idiomatic patterns (like using exceptions for control flow). It tends to always write Java even if it's Elixir. Usage rules help: https://hexdocs.pm/usage_rules/readme.html https://hexdocs.pm/usage_rules/readme.html
- majoe 8mo agoI tried different LLMs with various languages so far: Python, C++, Julia, Elixir and JavaScript. The SOTA models come do a great job for all of them, but if I had to rank the capabilities for each language it would look like this: JavaScript, Julia > Elixir > Python > C++ That's just a sample size of one, but I suspect, that for all but the most esoteric programming languages there is more than enough code in the training data.
- ogig 8mo agoI've used CC with TypeScript, JavaScript and Python. Imo TypeScript gives best results. Many times CC will be alerted and act based on the TypeScript compile process, another useful layer in it's context.
- dnautics 8mo agoI gave a talk about this. Without evidence, I suspect it's due to the "poisoning" phenomenon, only a few examples (~250 IIRC) is enough to push the needle, seemingly independent of LLM parameter count. Elixir has some really high quality examples available so, there is likely a "positive poisoning" effect.
- botacode 8mo agoGreat article that concretizes a lot of intuitions I've had while vibe coding in Elixir. We don't 100% AI it but this very much matches our experience, especially the bits about defensiveness. Going to do some testing this week to see if a better agents file can't improve some of the author's testing struggles.
- jonator 8mo agoI can attest to everything. Using Tidewave MCP to give your agent access to the runtime via REPL is a superpower, especially with Elixir being functional. It's able to proactively debug and get runtime feedback on your modular code as it's being written. It can also access the DB via your ORM Ecto modules. It's a perfect fit and incredibly productive workflow.
- manmal 8mo agoIs an MCP really required for this?
- dnautics 8mo agosure, you could in principle write a script that calls into the running vm, executes code, and just make this a text-based command attached to a script + skill. 6 of one one-half dozen of the other. At the point where you have a phoenix project in dev, you're already exposing an http endpoint, so the infra to not have to do a full on "attach to the VM and do RPCs" is nice, and you just pull tidewave in as a single dependency, instead of downloading a bunch of scripts, etc.
- ch4s3 8mo agoWhich models are you using? I’ve had mixed luck with GPT 5.2.
- jonator 8mo agoI've been using Opus 4.5 via Claude Code
- barkerja 8mo agoOpus 4.5 with Elixir has been remarkably good for me. I've been writing Elixir in production since ~2018 and it continues to amaze me at the quality of code it produces. I've been tweaking my skills to avoid nested cases, better use of with/do to control flow, good contexts, etc.
- 8mo ago
- tossandthrow 8mo agoIt seems like the 100% vibe coded is an exaggeration given that Claude fails at certain tasks. The new generation of code assistants are great. But when I dogmatically try to only let the AI work on a project it usually fails and shots itself in its proverbial feet. If this is indeed 100% vibe coded, then there is some magic I would love to learn!
- ogig 8mo agoMy last two projects have been 100% coded using Claude, and one has certain complexity. I don't think there is coming back for me.
- tossandthrow 8mo agoWhat is your secret sauce? How do you organize your project?
- ogig 8mo agoI decided to really learn what is going on, started with: https://karpathy.ai/zero-to-hero.html https://karpathy.ai/zero-to-hero.html That give a useful background into understanding what the tool can do, what context is, and how models are post trained. Context management is an important concept. Then I gave a shot to several tools, including copilot and gemini, but followed the general advice to use Claude Code. It's way better that the rest at the moment. And then I dive deep into Claude Code documentation and different youtube videos, there is plenty of good content out there. There are some ways to customize and increase the determinism of the process by using the tools properly. Overall my process is, define a broad spec, including architecture. Heavy usage of standard libraries and frameworks is very helpful, also typed languages. Create skills according to your needs, and use MCP to give CC a feedback mechanism, playwright is a must for web development. After the environment and initial seed is in place in the form of a clear spec, it's process of iteration via conversation. My session tend to go "Lets implement X, plan it", CC offers a few route, I pick what makes most sense, or on occasions I need to explain the route I want to take. After the feature is implemented we go into a cleanup phase, we check if anything might be going out of hand, recheck security stuff, and create testing. Repeat. Pick small battles, instead of huge features. I'm doing quite a lot of hand handling at the moment, saying a lots of "no", but the process is on another level with what I was doing before, and the speed I can get features out is insane.
- pmontra 8mo ago> In Elixir tests, each test runs in a database transaction that rolls back at the end. Tests run async without hitting each other. No test data persists. And it confuses Claude. This way of running tests is also what Rails does, and AFAIK Django too. Tests are isolated and can be run in random order. Actually, Rails randomizes the order so if the are tests that for any reason depend on the order of execution, they will eventually fail. To help debug those cases, it prints the seed and it can be used to rerun those tests deterministically, including the calls to methods returning random values. I thought that this is how all test frameworks work in 2026.
- netghost 8mo agoI did too, and I've had a challenging time convincing people outside of those ecosystems that this is possible, reasonable, we've been doing it for over a decade.
- vmg12 8mo agoWhy not just write to the db? Just make every test independent, use uuids / random ids for ids.
- szundi 8mo ago[dead]
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- mystifyingpoi 8mo ago> Just make every test independent That's easier said than done. Simple example: API that returns a count of all users in the database. The obvious correct implementation that will work would be just to `select count(*) from users`. But if some other test touches users table beforehand, it won't work. There is no uuid to latch onto here.
- epolanski 8mo agoI'm a bit lost on few bad and ugly points. They could've been sorted with precise context injection of claude.md files and/or dedicated subagents, no? My experience using Claude suggests you should spend a good amount of time scaffolding its instructions in documents it can follow and refer to if you don't want it to end in the same loops over and over. Author hasn't written on whether this was tried.
- viktorcode 8mo agoIt's the second time today when I see that the higher number of LoC is served as something positive. I would put it strictly in "Ugly" category. I understand the business logic that says that as long as you can vibe code away from any problems, what's the point of even looking at the code.
- esafak 8mo agoThink of it as 60 man-years of work.
- idle_zealot 8mo agoIf that's true then I can ship 60 man-years of work with yes 'println("a very important and useful line of code");' >> main.c in under a second!
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- esafak 8mo agoHow is that 60 man-years of work? You are not going to replicate what the LLM generated in under a second without the LLM.
- njhnjhnjh 8mo ago[flagged]
- quietbritishjim 8mo agoGenuinely hard to tell if satire. Just in case not, consider whether the short function def is_even(x): return (x%2) == 0 Handles a wider range of input conditions than the higher LOC function def is_even(x): if x == 0: return True if x == 2: return True if x == 4: return True ... return False
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- alecco 8mo agoAsync or mildly complex thread stuff is like kryptonite for LLMs.
- catlifeonmars 8mo agoAlso for humans.
- omnicognate 8mo ago[flagged]
- phplovesong 8mo ago"It writes 100% of our code" - Silently closes the tab, and makes a remark to avoid given software at any cost.
- Ronsenshi 8mo agoYou're not missing much. Seems to me like they wrote 150k lines of code for some glorified photo app with ChatGPT in the backend for image processing. Oh and some note-taking it seems.
- deadbabe 8mo agoEveryone always ends these articles with “I expect it will get better” What if it doesnt? What if LLMs just stay mostly the same level of usefulness they are now, but the costs continue to rise as subsidization wears off? Is it still worth it? Maybe, but not worth abandoning having actual knowledge of what you’re doing.
- solumunus 8mo agoI expect the costs at source will go down even if model performance doesn’t improve much, and hopefully that will offset the unraveling of subsidisation. I’d be happy enough with that outcome, I don’t really need them to be any better although of course it would be nice. I would love for them to be faster and cheaper.
- CyberDildonics 8mo agoIf it's not working now when extravagant amounts of money are being put into it, it might be time to just accept what it is and work around that instead of keeping all the grand predictions. Anyone can sell the future.
- deadbabe 8mo agoAll the money in the present has been taken, you can now only make money from the future.
- te_chris 8mo agoThe imperative thing is so frustrating. Even the latest models still write elixir like a JS developer, checking nils, maybe_do_blah helper functions everywhere. 30 lines when 8 would do.
- cpursley 8mo agoTry these: - https://github.com/agoodway/.claude/blob/main/skills/elixir-genius/SKILL.md https://github.com/agoodway/.claude/blob/main/skills/elixir-... - https://github.com/agoodway/.claude/blob/main/agents/elixir-expert.md https://github.com/agoodway/.claude/blob/main/agents/elixir-... - https://github.com/agoodway/.claude/blob/main/agents/elixir-qa.md https://github.com/agoodway/.claude/blob/main/agents/elixir-... Getting pretty good results so far.
- barkerja 8mo agoThese should get added to https://skills.sh/?q=elixir https://skills.sh/?q=elixir
- cpursley 8mo agohttps://skills.sh/agoodway/.claude/elixir-genius https://skills.sh/agoodway/.claude/elixir-genius
- simmanian 8mo agoHaven't used skills so far -- do you simply store them in your skills directory and have them automatically get used or do you have to specify one of the skills every time?
- cpursley 8mo agoYes regarding directory. They merged the concept of slash commands so I often do /elixir-genius to force it. Or if I just need subagents tell it to use "elixir-expert" or "elixir-qa" in parallel with other appropriate subagents. Also helps to put a mention in the Claude.md file.
- calvinmorrison 8mo agoI dont know erlang. My hobby LLM project is having it write a fully featured ERP in Erlang. An ERP is practically an OS. It now has - pluggable modules with a core system - Users/Roles/ACLs/etc. - an event system (IE so we can roll up Sales Order journal entries into the G/L) - G/L, SO, AR, AP - rollback/retries on transactions i havent written a line of code
- Sharlin 8mo agoI don’t understand how the author can simultaneously argue that Claude is great at Elixir because it’s a small language with only one paradigm, and also that Claude is bad at Elixir, spewing out non-idiomatic code that makes little sense in the functional paradigm?
- davidclark 8mo agoThe secret is that the author is also Claude.
- dnautics 8mo agook, so im "vibe-" building out my company's lab notebook in elixir ahead of the first funding check coming in. im doing some heavy duty shit, almost everything is routed through a custom CQRS-style events table before rollup into the db tables (the events are sequentially hashed for lab notebook integrity). editing is done through a custom implementation of quill js's delta OT. 100% of my tests are async. I've never once run into the ecto issues mentioned. I haven't had issues with genservers (but i have none* in my project). claude knows oban really well. Honestly I was always afraid to use oban until claude just suggesting "let's use oban" gave me the courage. I'll be sending Parker and Shannon a first check when the startup's check comes in. article is absolutely spot on on everything else. I think at this point what I've built in a month-ish would have taken me years to build out by myself. biggest annoyance is the over-defensiveness mentioned, and that Claude keeps trying to use Jason instead of JSON. Also, Claude has some bad habits around aliases that it does even though it's pretty explicitly mentioned in CLAUDE.md, other annoying things like doing `case functioncall() do nil -> ... end` instead of `if var = functioncall() do else` *none that are written, except liveviews, and one ETS table cache. [0] CQRS library: https://hexdocs.pm/spector/Spector.html https://hexdocs.pm/spector/Spector.html [1] Quill impl: https://hexdocs.pm/otzel/Otzel.html https://hexdocs.pm/otzel/Otzel.html
- andnand 8mo agoIm so confused by this. Watching the demos it seems like they just do some OCR to fill in a form? Then grab an email and linkedin url? The demo takes ~10s to do that.