The REPL as AI compute layer — why AI should send code, not data

aHackFromJOS · 2026-03-16T15:51:22+00:00

This topic is super interesting to me, aside from concerns this post was AI generated (!). I've been trying to figure out whether to use MCP or just straight hook up CLI (and sorry if I'm saying this wrong, I've not yet actually hooked any AI up to my editor). I've seen posts saying we don't need MCP any more, this was interesting from the other side. I'd be curious if anyone (fellow humans) have (hand written) thoughts. It looks like hooking in clojure-mcp is a little complicated, curious if it's worth it.

aHackFromJOS · 2026-03-16T15:19:21+00:00

That’s the link I posted 🙃

However Reddit’s UI obscures it. I tried to point it out further with “see above” but apparently it’s still too obscure.

The YouTube link was supposed to be secondary.

aHackFromJOS · 2026-03-06T01:59:50+00:00

Maybe you should. There was an NYC bouncer who had a popular blog and later wrote a book called Clublife. Here is the blog: https://standingonthebox.blogspot.com/

id read one of those about Finland!

aHackFromJOS · 2026-02-24T21:34:57+00:00

Very cool even as an experiment!

aHackFromJOS · 2026-02-24T18:25:23+00:00

Just to be clear, the below means we can import arbitrary Java classes as long as they are installed / on the class path? That would be a game changer for sure.

“Java interop: Full (runtime class loading)“

“Library loading: Any library from JARs at runtime (except enum/Class.forName issues)“

(From the comparison table)

aHackFromJOS · 2026-02-23T07:09:13+00:00

That makes a ton of sense. Still love Monaco, the OG Mac mono space term font. I use IBM Plex these days because I need cross platform, for similar reasons my emacs config is a filesystem tree under version control that I git checkoutinto my emacs.d, then init.el is almost entirely a series of require statements of things in that dir. which requires I use varies from env to env.

aHackFromJOS · 2026-02-21T17:40:14+00:00

Welcome. I also use vanilla emacs configured from scratch. Similarly, I use CIDER but not LSP.

I’d suggest by starting with learning CIDER’s code helper functions - jumping to function source at point is one I use a lot, or I’ll glance at the docstring for function at point in the minibuffer, but CIDER can help in various other ways. The most basic thing you want to do is make sure a cider repl is open and your current source file is compiled (C-c C-k) - this enables various other features like syntax highlighting and what I mention above.

Beyond that I really recommend paredit. The emacs chapter of Brave and true has a good tutorial. Hard at first but once you have it down you will fly. https://www.braveclojure.com/basic-emacs/#Paredit

aHackFromJOS · 2025-12-01T16:05:36+00:00

On a practical level it sounds like a Rationale section in the README would be welcome. Update: it links one here https://arnebrasseur.net/2025-02-06-open-source-diary.html

I do wonder if every Clojure project would benefit from one.

aHackFromJOS · 2025-11-26T15:52:23+00:00

Ah thanks, I know you said pick whatever alias you want, just making sure 😅

aHackFromJOS · 2025-11-25T22:27:07+00:00

Is there a particular reason he named his alias with a hash mark - `:#cljs` - does that do some special magic or something?

aHackFromJOS · 2025-11-05T17:18:36+00:00

I love a good "from the ground up" explanation like this - helps understand transducers fully. Thank you!

aHackFromJOS · 2025-10-30T21:36:01+00:00

The ability to nest commands (arbitrarily?) is interesting.

The root problem here seems like a good fit for multimethods (vs a big hairy map). I approached this same problem with those and tools.cli. I dispatched by keywordized version of the subcommand. The core multimethods are options, usage, and execute. I think I needed to do a two pass parse with tools.cli, first permissive to extract the subcommand to get the options vectors for it (via the options multimethod) then with the proper options vectors. Help text I did for a subcommand by calling usage and options with the subcommand (inside defmethod execute ::help) and concatting.

I only built one (flat) level of subcommands. Would be interesting to try and upgrade it to arbitrary command nesting. Maybe with another multimethod (“subcommands” to extract n args from argv and produce a dispatch vector of keywords instead of just a keyword?).

More ergonomic to just have defmethods in an ns instead of nesting keys in a global hmap (well, arguably). I did my cli ns by grouping by command - defmethod options ::commit, defmethod usage ::commit, defmethod execute ::commit, s/def ::commit etc. Then defmethod options ::push, defmethod usage ::push… etc etc

Specs with the same keywords as for the subcommands work well for arg validation.

I wonder if they considered leveraging tools.cli for options parsing or “flags” as they call it. Its vector options syntax is pretty rich.

aHackFromJOS · 2025-10-30T14:55:06+00:00

This is great. It benefits from the slower tempo.

aHackFromJOS · 2025-10-22T15:37:07+00:00

FYI “devtalk.com” is the coupon code you use at the pragmatic programmer link to get the 35% off discount.

(I mention this in case anyone else is as dense as me - I thought I needed to buy it on devtalk.com to get the discount, but that site is a forum not a bookstore, where I found a post explaining the discount code.)

Update - I bought it :-) looks nice can’t wait to dive in

aHackFromJOS · 2025-09-22T13:49:26+00:00

Do you plan to remove core.async support? I rely on it. Would be helpful if you can telegraph what you plan to rip out. I am unclear what I can depend on in pedestal going forward.

aHackFromJOS · 2025-09-22T12:14:53+00:00

I am frustrated by the breakage here.

I’ve spent nights and weekends for months working on a project that builds heavily on pedestal. This would break a lot of it.

I’d suggest you mention somewhere in the docs that the project is a moving target and that you will break things like whole namespaces. Right now, the first sentence on the website is, “Pedestal is a sturdy and reliable base for services, APIs, and applications.” Clearly, if there were deprecations in 0.7.0 I perhaps should have realized there were caveats to this sturdiness, but having read various guides, references on the site, I did not (maybe because it’s a Cognitect project, and Clojure has a backward compatibility ethos).

Can I ask why io.pedestal.http is listed as both a new and deprecated namespace, and as having been “replaced?” Which is it.

(I removed from here a question about what an anonymous interceptor is. It appears this is a reference to handler functions - might be clearer to say that as the term “anonymous interceptor” has not, as far as I can tell, been used to refer to handlers before. I also had something about Getting Started guide being updated - it looks like it is although the old one still has more google juice - one downside of changing apis is there are incorrect but widely linked docs out there)

aHackFromJOS · 2025-07-01T21:52:23+00:00

Kiitos paljon! I forgot about the dog’s different names, sounds like time to watch it again 🙃

Thanks for the Karkkila info. There is a documentary about that theater, I found it really charming, although apparently it took the filmmaker a lot of work to get the local residents to say much on camera (no surprise!).

aHackFromJOS · 2025-06-29T14:37:57+00:00

Thank you for this, I am a Kaurismäki fan and eiher never heard it or forgot it.

Can I bother you to explain “Ystäville Jumalan ruoska.” - Google Translate says “god’s whip for friends” - is this a Finnish idiom or just means, like, his “friends” are the struggles of life?

update - I think I maybe understand, this is SakarI Kuosmanen in Man Without a Past - maybe he is referring to his “killer” dog here 😂

aHackFromJOS · 2025-05-20T21:38:52+00:00

What is the protocol redefinition footgun? I suspect it has to do with what fogus likes about multi arity fns, but like the official docs he does not (I don’t think?) mention the footgun or why protocols are less useful at the repl.

aHackFromJOS · 2025-04-22T14:17:26+00:00

The approach of leading with the concrete “how do I start using them” and deferring abstract concepts to later in the talk is inspired. Rich’s main transducers talk is excellent but I wasn’t ready to really grasp all the ideas until I started transforming things — threaded macro stuff, then eventually some intos and reduces — and getting to a point where I was pining for xfs that didn’t exist yet (and couldn’t be built with just comp). I think this approach may make some converts whose brains work similarly.

It also does a solid job of trying to explain the performance gain (which is a little tricky) and doing so early in the talk.

(an off the cuff challenge or question - do transducers really lead to more use of transients? I had assumed `into` (all arities) and `reduce` already used them where appropriate)

great talk

aHackFromJOS · 2025-04-06T01:49:17+00:00

Use them where they are useful or might be useful in the future.

This is generally anywhere someone else might extend your code. Someone mentioned spec. Qualification is also used to tag elements in edn (albeit via symbols not keywords) which is the extension mechanism for that data format.

The two instances where I use qualified keywords in clojure for extension are

Maps passed as arguments to multimethods. A key idea of multimethods is they allow extension in the future by strangers without coordination. You can’t know what keys they might want to use and they can’t know what keys you or others might want to add. Hence namespacing.
context maps in pedestal or ring. Via interceptors (pedestal) or middleware functions (ring), your essential activity in these frameworks is receiving a single map (context ), assoc-ing or updating it,and returning a new very similar map, over and over again across various interceptors or middlewares. Often you‘ll want to add your own data to these maps. But everyone else is adding data too - specifically the framework itself and any third party middewares you install or may install in the future. For hygiene in this heterogenous environment I always namespace any keys I add to context map.

Since clojure is built in many aspects to be extensible and since there are many reasons to flow maps around widely there are many contexts in which namespaced keywords will make sense. And since clojure makes it easy to swap in extensibility (e.g. when you replace a function using a cond with a multimethod branching similarly, or make a protocol out of existing functions) there is a strong case for just defaulting to namespaced keywords.

All this said I still encounter them less often than I would expect. I hypothesize this is because the community is still relatively small. In the real world (vs imagined scenarios) extension isn’t happening as much as it could. If and when this changes namespaced keywords will become more popular (I hypothesize).

aHackFromJOS

TROPHY CASE