OCaml running on a 1960s UNIVAC 1219B

Community
1

Hi!

I’ve been meaning to post a recent-ish project of mine where I ran OCaml (and much more) on a 1960s UNIVAC 1219B! The demo I chose to run was a sudoku solver. In short, this was done by compiling OCaml to C, C to RISC-V, and then emulating RISC-V on the UNIVAC.

Full UNIVAC toolchain: Writeup, and source. Please see the my comment below for the other links! I’m unable to post more than two links in a post.

I also ran an OCaml program submitted by a friend that computed factors of numbers. At one point we thought the program crashed, but we were delighted when the program resumed ~5 minutes later. Turns out garbage collecting is slow on this machine :slight_smile:

Oh, and it works with OxCaml too!

Enjoy! Below are some pictures. (Disregard the earlier output, that was a run of ELIZA :slight_smile:)

image
image1920×2560 517 KB

image
image1920×1440 625 KB

27 Likes
2

OCaml to C: Writeup, and source

5 Likes
3

Sudoku solver source: OCaml, and compiled to C

4 Likes
4

Very cool to see OCaml on retro hardware like this!

2 Likes
5

Fantastic :heart_eyes: I need to try to adapt this for compilation for AVR microcontrollers (just for fun).

But why do you use Core? In my opinion, it’s overkill for everything except Jane Street itself.

6

After a few tweaks, I managed to get c_of_ocaml working to compile firmware for AVR microcontrollers! I went ahead and forked your project, completely refactoring it to support the latest version of the js_of_ocaml compiler.

open Hal

let () =
  gpio_mode 13 1;
  while true do
    led_on 13;
    delay_ms 1000;
    led_off 13;
    delay_ms 1000
  done
3 Likes
7

Thanks for sharing! I hadn’t seen c_of_ocaml before.

It was a tedious (but fun) evening project to rework your efforts to run OCaml on my Xbox 360:

ide
ide709×460 29.9 KB

Screenshot 2026-10-01 204948
Screenshot 2026-10-01 2049481065×631 111 KB

My teenage self would be very pleased.

5 Likes