I’m just a lightweight Cursor user building webapps. I rarely ask the AI to code Elixir for me. I often find myself unhappy with the result, or it simply takes more time to steer the AI into the right direction than it takes to write the code myself. Adding the Tidewave MCP server helped improve the workflow with the AI agent quite a bit, but I still find it lacking.

The hallucinations and stubbornness of the AI is a real problem for me. I have had repeated “arguments” trying to convince it that a function it hallucinated doesn’t exist…just to have it go “Oh you’re right, I’m so sorry…here’s a version that is guaranteed to work: produces similar output with hallucinated functions still there”

However, I do get real value out of Cursor when it comes to doing the stuff I don’t know that well - especially CSS. An oversimplified example might be me selecting a block of HTML, ctrl+k → “center this horizontally”, and Cursor spits out the correct Tailwind CSS to center the content (which varies based on context).

Claude doesn’t really know how to write OTP code by default. And I’m not a senior OTP dev by any means, not even a junior one yet. But, I have studied OTP, and with my limited background, it’s obvious that Claude really prefers (as of Sonnet and Opus 4) to write crappy OTP, when unrestricted.

Without explicit direction, Claude will sneak in brittle tests with concurrency issues, unsupervised processes, overuse of potentially runaway atoms, and all sorts of other beginner-level gotchas.

I’m working on enhancing credo checks to help enforce OTP compliance. You want to spawn? Is it supervised? Robust specification for OTP compliance are a must, for every context. The issues I’ve faced are also related to not having explicit definitions of the OTP design in-context. Going back to having the design worked out in advance, with the supervision tree worked out, clearly specified in the prompts, has been working better for me in testing. Going to try this approach again on the next go-around for my OTP app. Vibe coding for these scenarios isn’t really feasible at this time, except to prototype, sketch, or learn (how not to do things).

As for prompting, the best success I’ve had is to have Claude break down a complicated set of technical documents into self-contained prompts that, for each, assume no previous context, and include all required reading. Even then, I have to review the prompt file to ensure that all of the refs are self contained. Then it’s just a matter of ensuring all dialyzer/warnings/failures/credo issues are resolved before moving onto the next prompt. But, still, Claude will take shortcuts from time to time, so a skilled human reviewer ensuring Claude stays on track is still worth a lot.

Once the prompt is finished, I either /clear or just restart Claude Code from scratch for the next prompt.

Short prompts are better (in the sense of fewer TODO’s per prompt, all else equal). It might seem to take longer because now you’re recontextualizing on relatively smaller changes, but the shorter the context, the better. Less drift.

Another thought I had is that long sets of rules to follow don’t work consistently. Simply saying, “here are my OTP rules, build robust OTP” has mixed results. “Don’t use sleep to solve concurrency issues” works, until it drifts (happens faster than you’d expect, due to fighting the grain on Claude’s preferences). On my next go, the design will be worked out in advance with tight audit/checks for every prompt to ensure compliance. Just because all of your tests pass doesn’t mean the code is good. Just reiterating this main point: generalized guidelines at length will fall apart.

My Claude Code has tried to deploy to Fly.io without asking. But it didn’t use the “mix deploy” alias that would have actually worked.

And related to silent failures with your Map.get/3 example, it really likes to do defensive coding. As in it wants to check for both atom and string values.

I don’t think comparisons to junior/mid/high-level developers are useful. It’s all three at once. As in you can discuss design at the architectural level.

I love the idea of using an Obsidian vault for the docs!

I am using Amp Code with a curated AGENT.md file - the results are pretty dramatic - I’m regularly posting examples on X: https://x.com/mikehostetler

Amp allows sharing threads - so you can see my prompt and the entire flow here:

https://x.com/mikehostetler/status/1940794759398006957

Here’s another one with a link to the thread and the PR it produced

https://x.com/mikehostetler/status/1942223175787430245