Older HN users may recall when busy discussions had comments split across several pages. This is because the Arc [1] language that HN runs on was originally hosted on top of Racket [2] and the implementation was too slow to handle giant discussions at HN scale. Around September 2024 Dang et al finished porting Arc to SBCL, and performance increased so much that even the largest discussions no longer need splitting. The server is unresponsive/restarting a lot less frequently since these changes, too, despite continued growth in traffic and comments:

https://news.ycombinator.com/item?id=41679215

[1] https://paulgraham.com/arc.html

[2] https://racket-lang.org/

• rayiner

  today at 8:46 PM

  I love this comment:

  "Btw, we rolled this out over 3 weeks ago and I think you're the first person to ask about it on HN. There was one earlier question by email. I think that qualifies as a splash-free dive."

  I had no idea and I'm an HN addict!

  • dang

    today at 9:01 PM

    The "splash-free dive" metaphor came from the greatly missed sctb and was the springboard for much fun conversation at HNHQ.

    https://hn.algolia.com/?dateRange=all&page=0&prefix=true&que...

    • ashton314

      today at 9:18 PM

      I’m curious: was Arc running Racket BC or CS? I understand it got a big performance boost after switching to Chez Scheme.

  • philipkglass

    today at 8:56 PM

    I was the person who emailed him about it earlier.

    2024-09-05, me:

    On another topic, I just noticed that the 700+ comments on https://news.ycombinator.com/item?id=41445413 all render on a single page. Hurray! Is the pagination approach obsolete now? I know that you've commented several times about wanting to optimize the code so pagination wasn't necessary. I don't know if that's finished or if pagination will have to go on the next time there's a big breaking story.

    Dan G:

    Yes: the performance improvements I've been working on for years finally got deployed, so pagination is turned off for now.

    (In case you're curious, the change is that Arc now runs over SBCL instead of Racket.)

    ...

    Btw you're the only person I know of who's noticed this and pointed it out so far!

    I have very mixed feelings about how much I know about this site.

• e12e

  today at 9:11 PM

  I suppose this version of Arc for sbcl is different from what hn runs on?:

  https://github.com/pauek/arc-sbcl

  And there's no version of Anarki that runs on sbcl?:

  https://arclanguage.github.io/

• today at 8:47 PM

How come it is named like that? It's a product of some old school consortium?

I know that ford,gm etc also made some R&D into software

• kej

  today at 9:23 PM

  From the About page:

  >SBCL derives most of its code from CMU CL, created at Carnegie Mellon University. Radical changes have been made to some parts of the system (particularly bootstrapping) but many fundamentals (like the mapping of Lisp abstractions onto the underlying hardware, the basic architecture of the compiler, and much of the runtime support code) are only slightly changed. Enough changes have been made to the interface and architecture that calling the new system CMU Common Lisp would cause confusion - the world does not need multiple incompatible systems named CMU CL. But it's appropriate to acknowledge the descent from the CMU hackers (and post-CMU CMU CL hackers) who did most of the heavy lifting to make the system work. So the system is named Steel Bank after the industries where Andrew Carnegie and Andrew Mellon, respectively, made the big bucks.

• p_l

  today at 9:43 PM

  In addition to the official reference to CMU, there is a second origin for the name.

    SBCL - Sanely Bootstrappable Common Lisp
  

  You see, when SBCL was forked from CMU, a major effort was done so that it could be compiled using any reasonably complete Common Lisp implementation, unlike CMU CL. Because CMU CL essentially could only be compiled by itself, preferably in the same version, which meant compiling and especially cross-compiling was complex process that involved bringing the internal state of CMUCL process to "new version".

  SBCL redid the logic heavily into being able to host the core SBCL compiler parts in any mostly-complete (does not have to be complete!) ANSI CL implementation, then uses that to compile the complete form.

  Meaning you can grab SBCL source tarball, plus one of GNU clisp, ECL, Clozure CL, even GNU Common Lisp at one point, or any of the commercial implementations, including of course CMUCL, and C compiler (for the thin runtime support) and build a complete and unproblematic SBCL release with few commands

While great option, LispWorks and Allegro Common Lisp should not be overlooked, too many focus on SBCL + Emacs and then complain about Lisp tooling.

• cultofmetatron

  today at 8:30 PM

  > too many focus on SBCL + Emacs and then complain about Lisp tooling.

  well yea, lispworks and allegro are expensive commercial projects. I wish sbcl, the defacto best open source option had better tooling. emacs is great and all for the true believers but I'm an unwashed vscode user. For plenty of reasons I can't justify it in my startup but I'd love to spend more time working with common lisp for personal projects but my time is limited so I prefer clojure or rust.

• stackghost

  today at 8:59 PM

  I use emacs regularly (in fact I have it running right now) and I think the complaints against it are perfectly valid. Emacs is awesome in lots of ways, but it also really, really sucks in lots of other ways.

  But putting emacs aside, the SBCL tooling seems reasonable to me. The real reason I rarely reach for lisp these days is not the tooling, but because the Common Lisp library ecosystem is a wasteland of partial implementations and abandoned code bases.

  It's also been my experience that LLMs are better at writing more mainstream languages, especially "newbie-proof" languages like Go.

  In any case, I don't see why one would reach for Allegro or Lispworks over SBCL unless one really enjoys writing lisp by hand and needs specific features they offer that SBCL doesn't. I would imagine those features are vanishingly few.

Can we get a "(1999)" date on this, please? Only half joking becuase I see Common Lisp and, sure, I upvote ... but honestly, what's the purpose of this HN submission without context?

SBCL is obviously fantastic but let's contrast with another popular implementation: Embeddable Common Lisp. https://ecl.common-lisp.dev/

Top marks for SBCL performance but ECL can be a better fit for embedding into mobile applications, running on lighter weight hardware, and in the browser.

• tosh

  today at 7:33 PM

  nb: there is a SBCL release at end of every month: https://www.sbcl.org/all-news.html

  • dang

    today at 9:03 PM

    We upgraded to 2.6.1 about a week ago and switched to using the new(ish) parallel(ish) garbage collector. I still can't tell what the impact has been.

    Claude Code (which is a wizard at analyzing log files but also, I fear, an incorrigible curve-fitter) insisted that it was a real breakthrough and an excellent choice! On the other hand there was a major slowdown last night, ending in SBCL dying from heap exhaustion. I haven't had a chance to dig into that yet.

    • stackghost

      today at 9:42 PM

      >SBCL dying from heap exhaustion

      Due to hitting the cap, or to framentation? My understanding is the new parallel GC compacts the heap rather infrequently.

  • emptybits

    today at 7:59 PM

    Thanks. Your link gives more insight into "why submit now?" Appreciate it.

My favorite bit of SBCL trivia is the name: this is descended from Carnegie Mellon's build.

Steel. Bank.

• giraffe_lady

  today at 8:02 PM

  That's very fun and makes so much more sense than my half guess that it was from a defunct regional mid 20th century bank I had never heard of.

• wiz21c

  today at 7:45 PM

  I don't get it :-(

  • wk_end

    today at 7:50 PM

    I think it's just that Andrew Carnegie made his fortune in the steel industry, and the Mellons made their fortune in banking.

    • PantaloonFlames

      today at 8:19 PM

      Yes and

      Carnegie Technical Schools was founded in 1900 based on a $1m donation from Andrew Carnegie,

      Mellon Institute of Industrial Research was originally founded in 1913 by Andrew and Richard Mellon.

      Carnegie Mellon was created by combining the two institutions in 1967.

the HN migration from Racket to SBCL is probably the best real-world case study for SBCLs native code compiler quality. going from pages of comments needing pagination to rendering everything in one shot is not a minor optimization - thats an order of magnitude improvement in throughput for a real production workload.

what doesnt get mentioned enough is SBCLs type inference. if you add type declarations to hot paths, the compiler generates code that rivals hand-optimized C. the REPL-driven development workflow where you can redefine functions in a running system is still unmatched by anything in the modern tooling ecosystem.

What about it?

• tmtvl

  today at 8:16 PM

  It's awesome and the lucky 10,000 deserve to be introduced to it?

  • mikestorrent

    today at 8:48 PM

    A well known quantum computing company's entire stack runs on SBCL, with Emacs in production... works really well, don't knock it until you've tried it. Phenomenal REPL.

    • iainctduncan

      today at 9:23 PM

      Would this be the same place that Coalton came out of? (just curious)

• oytis

  today at 7:46 PM

  It's a recurrent event when someone on HN discovers some well-known piece of technology.

  • jjtheblunt

    today at 8:55 PM

    agreed, but "tosh" posted numerous times on SBCL over the last 7 years, so it's a valid question.

    https://hn.algolia.com/?q=tosh+sbcl