Foundations for hacking on OCaml
10 Nov 2025How do you acquire the fundamental computer skills to hack on a complex systems project like OCaml? What’s missing and how do you go about bridging the gap?
How do you acquire the fundamental computer skills to hack on a complex systems project like OCaml? What’s missing and how do you go about bridging the gap?
Can we have OCaml notebooks as pure client-side code? Can these notebooks have rich editor support (highlighting, formatting, types on hover, autocompletion, inline diagnostics, etc.)? Can you take packages from OPAM and use them in these notebooks?
The answer to all of these turns out to be a resounding yes thanks for
x-ocaml. This post is my experiment playing
with x-ocaml and integrating that into this blog.
In the last post, we looked at uniqueness mode and how uniqueness may be used to optimise. As we will see, uniqueness alone is insufficient in practice, and we also need a concept of linearity for uniqueness to be useful.
Jane Street has been developing modal types for OCaml – an extension to the type system where modes track properties of values, such as their scope, thread sharing, and aliasing. These modes restrict which operations are permitted on values, enabling safer and more efficient systems programming. In this post, I focus on the uniqueness mode, which tracks aliasing, and show how it can eliminate certain runtime checks.
Recently, I posted on X and LinkedIn that I am always looking for excellent people to join my group. I received a lot of enquiries, some of which led to internship hires (yay!). But mostly, I seemed to offer similar advice. I thought I’d write a post that summarise my responses.
Off-CPU analysis is where the program behavior when it is not running is
recorded and analysed. See Brendan Gregg’s eBPF based off-CPU
analysis. While on-CPU
performance monitoring tools such as perf give you an idea of where the
program is actively spending its time, they won’t tell you where the program
is spending time blocked waiting for an action. Off-CPU analysis reveals
information about where the program is spending time passively.
A number of folks who regularly use OCaml were surprised to learn that you can reasonably debug OCaml programs using gdb. The aim of the post is to show the first steps in using gdb on OCaml programs.
Last semester at IIT Madras, I taught a revamped core course CS3100 Paradigms of Programming, which introduces 3rd-year students to functional and logic programming paradigms. While the course had been traditionally offered in Lisp and Prolog, I introduced OCaml instead of Lisp. All of the lectures were delivered through interactive Jupyter notebooks. The assignments were also distributed as Jupyter notebooks and evaluated through autograder facility in Jupyter. There has since been several requests to replicate this setup elsewhere. Hence, I thought I should write about the set up and experience of teaching through Jupyter notebooks.
Multiple Research Software Engineer positions are available in the Department of Computer Science and Engineering at the Indian Institute of Technology, Madras to develop Multicore OCaml and enable Tezos ecosystem to benefit from Multicore OCaml.
Multicore OCaml comes with a concurrent garbage collector, where the garbage collector and the mutator threads run concurrently. Debugging concurrent GC bugs has been the most frustrating / satisfying (when fixed) part of Multicore OCaml development. rr, a record and replay tool has made debugging concurrent GC bugs a sustainable exercise. In this short post, I’ll describe why.