It'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.
> Remember, there used to be a time programmers productivity was measured in LoC per hour.
Do you remember such a time or company? I have been developing professionally since the early 1990's (and hobbyist before then), and this "truth" has been a meme even back then.
I'm sure it happened, but I'm not sure it was ever as widespread as this legend would make it sound.
But, there were decades of programmers programming before I started, so maybe it just predated even me.
Yes, as we all know, when evaluating which programming language to use, you should get a line count of the compiler's repo. More lines = more capabilities.
Why would I ever want a language with less capabilities?
> 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.
I 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.
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.
Frankly this is the better solution for async tests. If the app can handle multiple users interacting with it simultaneously, then it can handle multiple tests. If it can’t, then the dev has bigger problems.
As for assertions, it’s not that hard to think of a better way to check if you made an insertion or not into the db without writing “assert user_count() == 0”
I 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.
Some MCP's do give the models superpowers. Adding playwright MCP changed my CC from mediocre frontend skills, to really really good. Also, it gives CC a way to check what it's done, and many times correct obvious errors before coming back at you. Big leap.
sure, 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.
Opus 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.
ok, 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.
It 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!
I think by 100% vibe coded most people on hn mean that 100% of the code is written not by hand. The hand only does the delete key and prompting. We're mostly not talking about amateurs with no CS background just prompting and shitting out software with all sorts of bugs they would never be able to see.
I 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?
It'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.
I 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.
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.
I 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.
I'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.
You can accurately describe elixir syntax in a few paragraphs, and the semantics are pretty straightforward. I’d imagine doing complex supervision trees falls flat.
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.
The 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.
Haven'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?
I 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 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.
You'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.
It'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.
Think of it as 60 man-years of work.
If that's true then I can ship 60 man-years of work with
in under a second!
Remember, there used to be a time programmers productivity was measured in LoC per hour.
As such, this is high productivity! /s
> Remember, there used to be a time programmers productivity was measured in LoC per hour.
Do you remember such a time or company? I have been developing professionally since the early 1990's (and hobbyist before then), and this "truth" has been a meme even back then.
I'm sure it happened, but I'm not sure it was ever as widespread as this legend would make it sound.
But, there were decades of programmers programming before I started, so maybe it just predated even me.
2 replies →
[flagged]
Yes, as we all know, when evaluating which programming language to use, you should get a line count of the compiler's repo. More lines = more capabilities.
Why would I ever want a language with less capabilities?
1 reply →
> to the extent that our systems' world models are effectively indistinguishable from the real world.
https://genius.com/Jorge-luis-borges-on-exactitude-in-scienc...
Genuinely hard to tell if satire.
Just in case not, consider whether the short function
Handles a wider range of input conditions than the higher LOC function
'Means' according to what? Put some (laughtable) reference so I can laught louder.
> 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.
I 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.
Story of my life in so many dimensions.
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> And it confuses Claude.
I've never had this problem.
Why not just write to the db? Just make every test independent, use uuids / random ids for ids.
> 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.
3 replies →
Frankly this is the better solution for async tests. If the app can handle multiple users interacting with it simultaneously, then it can handle multiple tests. If it can’t, then the dev has bigger problems.
As for assertions, it’s not that hard to think of a better way to check if you made an insertion or not into the db without writing “assert user_count() == 0”
[dead]
I 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.
Some MCP's do give the models superpowers. Adding playwright MCP changed my CC from mediocre frontend skills, to really really good. Also, it gives CC a way to check what it's done, and many times correct obvious errors before coming back at you. Big leap.
Is an MCP really required for this?
sure, 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.
Which models are you using? I’ve had mixed luck with GPT 5.2.
Opus 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.
1 reply →
I've been using Opus 4.5 via Claude Code
Great 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.
ok, 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
[1] Quill impl: https://hexdocs.pm/otzel/Otzel.html
It 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!
I think by 100% vibe coded most people on hn mean that 100% of the code is written not by hand. The hand only does the delete key and prompting. We're mostly not talking about amateurs with no CS background just prompting and shitting out software with all sorts of bugs they would never be able to see.
My last two projects have been 100% coded using Claude, and one has certain complexity. I don't think there is coming back for me.
What is your secret sauce? How do you organize your project?
3 replies →
I 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?
The secret is that the author is also Claude.
It'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.
I 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.
I 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.
> 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
I 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.
I'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.
You can accurately describe elixir syntax in a few paragraphs, and the semantics are pretty straightforward. I’d imagine doing complex supervision trees falls flat.
Unless that new language has truly esoteric concepts, it's trivial to pattern-match it to regular programming constructs (loops, functions, ...)
I'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.
Async or mildly complex thread stuff is like kryptonite for LLMs.
Also for humans.
[flagged]
The 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.
Try these:
- https://github.com/agoodway/.claude/blob/main/skills/elixir-...
- https://github.com/agoodway/.claude/blob/main/agents/elixir-...
- https://github.com/agoodway/.claude/blob/main/agents/elixir-...
Getting pretty good results so far.
Haven'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?
1 reply →
These should get added to https://skills.sh/?q=elixir
[flagged]
Are you trolling ?
I 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
Everyone 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.
I 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.
"It writes 100% of our code"
- Silently closes the tab, and makes a remark to avoid given software at any cost.
You'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.
I await (also doubt) the day this produces something truly useful and not just generic derivative functionality glued together