https://patrick.sirref.org/part-ii-geocaml/ part-ii-geocaml /part-ii-geocaml/ Effective Geospatial Code in OCaml This project is co-supervised with Michael Dales. Geospatial processing is critical in environmental science and is used in a range of environmental scenarios, both in areas of carbon accounting like digital Monitoring, Reporting and Verification in Reforestation Carbon Removal, and also biodiversity analysis like calculating worldwide extinction rates. I will write a non-blocking library for reading GeoTIFF files in OCaml (built on top of the WIP OCaml-TIFF library1 written by one of my supervisors, Patrick Ferris). I will then use OCaml to write an embedded Domain Specific Language (eDSL) which will be used to interact with geospatial data in a declarative way. References Context 2024 9 10 https://patrick.sirref.org/part-ii-2024/ part-ii-2024 /part-ii-2024/ Part II Students 2024 In the final year of the Cambridge undergraduate degree in computer science, students undertake a coding project with an accompanying dissertation. https://patrick.sirref.org/part-ii-hazel/ part-ii-hazel /part-ii-hazel/ Type Error Debugging in Hazel This project will add some features to the Hazel language. Hazel is a functional research language that makes use of gradual types to support unusual features such as: holes (code place-holders) to give type meaning to incomplete programs. Importantly for this project, all Hazel programs, even ill-typed or incomplete programs, are evaluable. This allows dynamic reasoning about ill-typed programs via evaluation traces with the potential to improve the user’s understanding of why ill-typed programs go wrong. This project aims to exploit further this potential by providing some extra features to both: aid with finding values/inputs that demonstrate why type-errors were found (type-error witnesses) and linking the evaluation traces back to source code. https://patrick.sirref.org/part-ii-udsl/ part-ii-udsl /part-ii-udsl/ A Universal Data Access DSL The design and implementation of a jq-like EDSL allowing programmers to abstract away the format in which data is stored (YAML, EXIF metadata etc.) and the file system being used – e.g. could mean "fields c, d in YAML file b of ZIP file a", or it could mean "fields b.c, b.d in JSON file a". My project would statically examine the filesystem to decide which case we're in, giving data scientists an easy way to declare the shape of the data they depend on. Success criteria include projection (correctly reading the data based on the file type), subtyping (e.g. JSON-LD is a child of JSON) and perhaps some compiler optimisations related to parsing (e.g. only loading a JSON library if the file is actually JSON). https://patrick.sirref.org/part-ii-paraeff/ part-ii-paraeff /part-ii-paraeff/ Implementing Parallel Algebraic Effect Handlers in OCaml Algebraic effects are becoming increasingly common, but it can be difficult to use them in parallel computations. Xie et al. (2024) present a new structure for effect handlers which allows parallel subcomputations to perform effects independently without synchronisation. I plan to implement the traverse handler in OCaml 5 and evaluate its performance against equivalent programs which do not use effects using a variety of benchmark programs. As extensions, I will devise similar handlers for other types of parallelism, possibly including a more general form which works for many types simultaneously, and investigate how to improve its real-world performance. https://patrick.sirref.org/part-ii-geocaml/ part-ii-geocaml /part-ii-geocaml/ Effective Geospatial Code in OCaml This project is co-supervised with Michael Dales. Geospatial processing is critical in environmental science and is used in a range of environmental scenarios, both in areas of carbon accounting like digital Monitoring, Reporting and Verification in Reforestation Carbon Removal, and also biodiversity analysis like calculating worldwide extinction rates. I will write a non-blocking library for reading GeoTIFF files in OCaml (built on top of the WIP OCaml-TIFF library1 written by one of my supervisors, Patrick Ferris). I will then use OCaml to write an embedded Domain Specific Language (eDSL) which will be used to interact with geospatial data in a declarative way. Backlinks Patrick Ferris 2026 9 30 https://patrick.sirref.org/weekly-2026-w39/ weekly-2026-w39 /weekly-2026-w39/ Weekly 2026 w39 Patrick Ferris 2026 9 30 Shells Work on the msh paper continued this week. One interesting result (for an appendix) was seeing what were the most commonly used commands in the Dockerfile dataset: Which again, leads to some notion of overkill in terms of using a shell as the means to create container images when all we do is move some files around and install packages! I'm wondering if we're missing a real opportunity to streamline this process via something like the package calculus -- a package manager-agnostic means for declaring your dependencies. Embed that as a programmable notion in your container image language alongside a container image-aware HTTP GET tool (to replace a vast majority of curl calls) and a handful of busybox commands, and you are left with (nearly) the raw shell only being used for the long tail of domain-specific things (e.g. invoking a build system). Patrick Ferris 2026 9 30 Joy in old documents I'll talk about the joy I found in reading some historical bits and bobs tracking down information about shells, containers and operating systems more generally. Part of this archaeological effort was trying to find when CHROOT was introduced into UNIX. Various online tools, including AI summaries, point to UNIX v7 but the system call is not obviously defined there. A bit more digging reveals it is listed under CHDIR(2) and not on its own. Anyway, flicking through the manual was somewhat of a joy. The preface reads: This new form of the Seventh Edition manual attests to the gratifying popularity of the UNIX Operating System. Delivered with no support and with an amateurishly published manual, this elegant and productive system has nevertheless earned worldwide respect, sometimes bordering on adulation... Thousands of users today work from faint reproductions of reproductions of the original manual, whose ragged pages dangle and slide out of beat-up ring binders... This bordering-on-poetic prose reminds me of some passages written for the MULTICS manual too (which I have talked about before). All to say, I'm often thinking about the importance of writing these days and injecting some personality into it. Patrick Ferris 2026 9 30 Part II Discussions I am hopefully going to supervise a part II project this year either on a fun ergonomic frontend to eBPF programs or a new spin on the geospatial DSL. More to follow once things are finalised. Patrick Ferris 2026 9 30 Upstreaming Forester Pretty-printer I finally got around to upstreaming the Forester pretty-printing API I have been using in Graft. This allows you to print, hopefully, syntactically correct Forester code directly from the AST (a Code.t in forester parlance). Happily, this all took place on tangled. It will be nice to keep this updated alongside Forester and point Graft to it. It feels like many people are moving away from a community-oriented model of software development, instead building a hybrid bazaarian cathedral monorepo powered by AI. I'm not here to really say what is right and what is wrong, but it seems to me that the sense of community is fragmenting and undue stress is being placed on many maintainers who no longer enjoy their job. Patrick Ferris 2026 9 30 https://patrick.sirref.org/ppx_deriving_yamlx-release/ ppx_deriving_yamlx-release /ppx_deriving_yamlx-release/ New release of ppx_deriving_ Raphael has proposed a new yamlx backend for ppx_deriving_yaml. It seems Ahrefs have been using his patch. I rejigged that PR to parameterise ppx_deriving_yaml over a small set of constructors and patterns so that the core codec logic could be reused. I am fairly pleased with this abstraction. It allows any data format that supports objects and list to reuse the codec. For example, it would be trivial now to add a ppx_deriving_cbor. Related https://patrick.sirref.org/mdales/ mdales /mdales/ Michael W. Dales https://digitalflapjack.com Contributions