# \#core **URL:** https://discuss.ocaml.org/tag/core/61.md [Latest](https://discuss.ocaml.org/latest.md) · [Categories](https://discuss.ocaml.org/categories.md) · [Tags](https://discuss.ocaml.org/tags.md) --- ## [Jane Street Libraries (base/core/async/etc) with 5.5](https://discuss.ocaml.org/t/jane-street-libraries-base-core-async-etc-with-5-5/18469)
**Author:** [@smuenzel](https://discuss.ocaml.org/u/smuenzel)\ **Replies:** 1\ **Last updated:** [August 25, 2026, 12:06pm UTC](https://discuss.ocaml.org/t/jane-street-libraries-base-core-async-etc-with-5-5/18469 "2026-08-25T12:06:01Z")
(Note: much of the linked repos are modified with the the help of LLMs, so please do check the diff to the upstream version before installing. Most diffs are very small. Also, this release is not affiliated with Jane Str… --- ## [Where are the docs for core, async?](https://discuss.ocaml.org/t/where-are-the-docs-for-core-async/17783)
**Author:** [@vivanov](https://discuss.ocaml.org/u/vivanov)\ **Replies:** 5\ **Last updated:** [February 7, 2026, 10:55pm UTC](https://discuss.ocaml.org/t/where-are-the-docs-for-core-async/17783 "2026-02-07T22:55:27Z")
There are no docs on the web page any more. E.g. core v0.17.1 (latest) · OCaml Package --- ## [SSL certificates error with websockets client connecting to localhost](https://discuss.ocaml.org/t/ssl-certificates-error-with-websockets-client-connecting-to-localhost/17787)
**Author:** [@vivanov](https://discuss.ocaml.org/u/vivanov)\ **Replies:** 3\ **Last updated:** [February 7, 2026, 10:27pm UTC](https://discuss.ocaml.org/t/ssl-certificates-error-with-websockets-client-connecting-to-localhost/17787 "2026-02-07T22:27:50Z")
Hey, I am getting an error when using the cohttp\_async\_websocket package. I am connecting to localhost (monitor.ml.Error (Ssl\_error ("error:0A000086:SSL routines::certificate verify failed") src/ssl.ml:201:20) ("Cal… --- ## [Testing with different number of lines of the same file](https://discuss.ocaml.org/t/testing-with-different-number-of-lines-of-the-same-file/17785)
**Author:** [@vivanov](https://discuss.ocaml.org/u/vivanov)\ **Replies:** 2\ **Last updated:** [February 7, 2026, 2:42pm UTC](https://discuss.ocaml.org/t/testing-with-different-number-of-lines-of-the-same-file/17785 "2026-02-07T14:42:10Z")
Hey, I have a 10 million line file I run tests with. I test with different number of lines there, e.g. first with 1k lines, then 100k lines, then 1m lines. Rather than creating several files with different amount of line… --- ## [\[Real world Ocaml\] How do I import core\_unix time?](https://discuss.ocaml.org/t/real-world-ocaml-how-do-i-import-core-unix-time/15964)
**Author:** [@nvm](https://discuss.ocaml.org/u/nvm)\ **Replies:** 2\ **Last updated:** [October 27, 2025, 3:58am UTC](https://discuss.ocaml.org/t/real-world-ocaml-how-do-i-import-core-unix-time/15964 "2025-10-27T03:58:58Z")
So, I’ve been following Real World OCaml, the 2nd edition and I hit a block I’m afraid I cannot overcome with google, documentation or AI help. The code in question: open Core let () = Out\_channel.output\_string stdo… --- ## [JaneStreet's OCaml Core library's Hashtbl interfaces](https://discuss.ocaml.org/t/janestreets-ocaml-core-librarys-hashtbl-interfaces/15323)
**Author:** [@s.t.s](https://discuss.ocaml.org/u/s.t.s)\ **Replies:** 16\ **Last updated:** [September 28, 2024, 9:59pm UTC](https://discuss.ocaml.org/t/janestreets-ocaml-core-librarys-hashtbl-interfaces/15323 "2024-09-28T21:59:56Z")
Available Hash Table APIs The question is about which approach to constructing a hash table in Core is preferable. I noticed that the JaneStreet’s Core Hashtbl library provides several interfaces to creating hash table… --- ## [Any benefit in using Async when reading a file?](https://discuss.ocaml.org/t/any-benefit-in-using-async-when-reading-a-file/15220)
**Author:** [@vivanov](https://discuss.ocaml.org/u/vivanov)\ **Replies:** 1\ **Last updated:** [August 31, 2024, 1:56am UTC](https://discuss.ocaml.org/t/any-benefit-in-using-async-when-reading-a-file/15220 "2024-08-31T01:56:08Z")
Hi. I read a file line by line and do some processing for each line. If I were to use Async to read line by line instead of ordinary reading a file via an Inchannel.input\_line, will there be any difference in performance… --- ## [Why does ppx\_base 0.17 not support windows installation while 0.16 does?](https://discuss.ocaml.org/t/why-does-ppx-base-0-17-not-support-windows-installation-while-0-16-does/14897)
**Author:** [@MaxHaydenChiz](https://discuss.ocaml.org/u/MaxHaydenChiz)\ **Replies:** 4\ **Last updated:** [July 4, 2024, 8:30pm UTC](https://discuss.ocaml.org/t/why-does-ppx-base-0-17-not-support-windows-installation-while-0-16-does/14897 "2024-07-04T20:30:02Z")
I was toying around with the new opam’s windows support and tried to use to it to install core. Core depends on ppx\_base. But opam kept wanting to install 0.16.x and would then fail at compiling it. (I think it fails bec… --- ## [Asking for the correct way to use Core module with functor and \`sexp\`](https://discuss.ocaml.org/t/asking-for-the-correct-way-to-use-core-module-with-functor-and-sexp/13163)
**Author:** [@arbipher](https://discuss.ocaml.org/u/arbipher)\ **Replies:** 3\ **Last updated:** [October 5, 2023, 11:37pm UTC](https://discuss.ocaml.org/t/asking-for-the-correct-way-to-use-core-module-with-functor-and-sexp/13163 "2023-10-05T23:37:07Z")
I have this code that works. open Core module Int = struct module T = struct type t = int \[@@deriving compare, sexp\] end include T include Comparator.Make (T) end type m = string Map.M(Int).t \[@@deriving … --- ## [Where to find Heaps in Core?](https://discuss.ocaml.org/t/where-to-find-heaps-in-core/11191)
**Author:** [@Neypot](https://discuss.ocaml.org/u/Neypot)\ **Replies:** 2\ **Last updated:** [January 16, 2023, 1:11am UTC](https://discuss.ocaml.org/t/where-to-find-heaps-in-core/11191 "2023-01-16T01:11:35Z")
Since there are no heaps in the standard library, I did a bit of research to find a usable module. This post on StackOverflow mentionned a submodule Heap in the Core.Std module. However, this module does not exist anymor… --- ## [How to get access to \`Map.Tree\` in Core v0.15.0?](https://discuss.ocaml.org/t/how-to-get-access-to-map-tree-in-core-v0-15-0/10950)
**Author:** [@grievejia](https://discuss.ocaml.org/u/grievejia)\ **Replies:** 3\ **Last updated:** [December 13, 2022, 8:01pm UTC](https://discuss.ocaml.org/t/how-to-get-access-to-map-tree-in-core-v0-15-0/10950 "2022-12-13T20:01:09Z")
I’m trying to upgrade core to v0.15.0 today and ran into issues with breaking API changes. Specifically, the Core.Map.Tree module seems to be gone (is this documented anywhere?). I saw there’s this new Core.Map.Make\_tre… --- ## [How to use Core.Command monadic operator cleanly (with many arguments function](https://discuss.ocaml.org/t/how-to-use-core-command-monadic-operator-cleanly-with-many-arguments-function/9018)
**Author:** [@Wulfman](https://discuss.ocaml.org/u/Wulfman)\ **Replies:** 10\ **Last updated:** [December 16, 2021, 10:33pm UTC](https://discuss.ocaml.org/t/how-to-use-core-command-monadic-operator-cleanly-with-many-arguments-function/9018 "2021-12-16T22:33:32Z")
I’m writing a CLI with Core.command and to write the command I need to apply a function f : 'a1 -\> 'a2 -\> ... -\> 'an -\> unit -\> unit to arguments 'a1 t, 'a2 t, ... 'an t after trying some stuff, I ended up finding monadi… --- ## [Jane Street packages: dropping support for 32-bit](https://discuss.ocaml.org/t/jane-street-packages-dropping-support-for-32-bit/8621)
**Author:** [@Arseniy\_Alekseyev](https://discuss.ocaml.org/u/Arseniy_Alekseyev)\ **Replies:** 23\ **Last updated:** [November 5, 2021, 8:12pm UTC](https://discuss.ocaml.org/t/jane-street-packages-dropping-support-for-32-bit/8621 "2021-11-05T20:12:53Z")
In Jane Street we plan to stop maintaining the compatibility of our open source packages with 32-bit architectures. This includes everything published on Jane Street · GitHub. We are not going to deliberately break thi… --- ## [Goodbye Core\_kernel](https://discuss.ocaml.org/t/goodbye-core-kernel/8393)
**Author:** [@jeremiedimino](https://discuss.ocaml.org/u/jeremiedimino)\ **Replies:** 7\ **Last updated:** [August 31, 2021, 4:11pm UTC](https://discuss.ocaml.org/t/goodbye-core-kernel/8393 "2021-08-31T16:11:26Z")
Hi, just a heads up that the Core\_kernel library from Jane Street will eventually disappear, leaving place to only Base and Core. More details in this blog post on our website: This change is good but is not backward … --- ## [Advantage of Int63 compared to Int64?](https://discuss.ocaml.org/t/advantage-of-int63-compared-to-int64/7465)
**Author:** [@mudrz](https://discuss.ocaml.org/u/mudrz)\ **Replies:** 13\ **Last updated:** [March 16, 2021, 4:51pm UTC](https://discuss.ocaml.org/t/advantage-of-int63-compared-to-int64/7465 "2021-03-16T16:51:20Z")
this is probably a stupid question, but - why does Base have Int63? the docs have a description: https://ocaml.janestreet.com/ocaml-core/latest/doc/base/Base/Int63/index.html The size of Int63 is always 63 bits. On a… --- ## [Is Core Nano\_mutex a replacement for Mutex from stdlib?](https://discuss.ocaml.org/t/is-core-nano-mutex-a-replacement-for-mutex-from-stdlib/6986)
**Author:** [@BikalGurung](https://discuss.ocaml.org/u/BikalGurung)\ **Replies:** 7\ **Last updated:** [December 17, 2020, 4:31pm UTC](https://discuss.ocaml.org/t/is-core-nano-mutex-a-replacement-for-mutex-from-stdlib/6986 "2020-12-17T16:31:59Z")
Is Core Nano\_mutex a replacement for Mutex from stdlib when using core ? Nano Mutex --- ## [How to prevent incomming async\_rpc's from delaying/starving high priority jobs](https://discuss.ocaml.org/t/how-to-prevent-incomming-async-rpcs-from-delaying-starving-high-priority-jobs/6686)
**Author:** [@Cjen1](https://discuss.ocaml.org/u/Cjen1)\ **Replies:** 16\ **Last updated:** [November 2, 2020, 6:59pm UTC](https://discuss.ocaml.org/t/how-to-prevent-incomming-async-rpcs-from-delaying-starving-high-priority-jobs/6686 "2020-11-02T18:59:01Z")
I’m working on a paxos implementation and am currently using the Async\_rpc library for my communcation layer. The issue I’m having is that when the system is under load, the client requests coming in mean that the data g… --- ## [Async writer, how do writes and fsync interleve](https://discuss.ocaml.org/t/async-writer-how-do-writes-and-fsync-interleve/6541)
**Author:** [@Cjen1](https://discuss.ocaml.org/u/Cjen1)\ **Replies:** 2\ **Last updated:** [October 4, 2020, 7:11am UTC](https://discuss.ocaml.org/t/async-writer-how-do-writes-and-fsync-interleve/6541 "2020-10-04T07:11:38Z")
Yet another how to async question :slight\_smile: I’m trying to write a relatively low latency write ahead log. I had it running in Lwt but after seeing how high performance the rpc library was I am porting it over to As… --- ## [Async rpc: how to make a persistant rpc connection](https://discuss.ocaml.org/t/async-rpc-how-to-make-a-persistant-rpc-connection/6536)
**Author:** [@Cjen1](https://discuss.ocaml.org/u/Cjen1)\ **Replies:** 2\ **Last updated:** [October 1, 2020, 5:12pm UTC](https://discuss.ocaml.org/t/async-rpc-how-to-make-a-persistant-rpc-connection/6536 "2020-10-01T17:12:16Z")
Hi all I’m trying to get my head around how the Async ecosystem connects together. I’m aiming to have a persistant rpc connection to some set of services. I can see that there is a way to create persistant connections: P… --- ## [Core\_kernel Comparator and polymorphism](https://discuss.ocaml.org/t/core-kernel-comparator-and-polymorphism/6173)
**Author:** [@milo](https://discuss.ocaml.org/u/milo)\ **Replies:** 4\ **Last updated:** [July 31, 2020, 7:19pm UTC](https://discuss.ocaml.org/t/core-kernel-comparator-and-polymorphism/6173 "2020-07-31T19:19:25Z")
OCaml newbie here. I’ve run into a problem I’m struggling to resolve. I’m working on an existing codebase, and I’d like to refactor one of its functions, which has the interface: let do\_something (l : 'a list) : 'a lis… --- ## [In Core, how does the \`compare\` function (of keys) affect the performance of a hash table?](https://discuss.ocaml.org/t/in-core-how-does-the-compare-function-of-keys-affect-the-performance-of-a-hash-table/5661)
**Author:** [@trungta](https://discuss.ocaml.org/u/trungta)\ **Replies:** 3\ **Last updated:** [May 1, 2020, 4:18pm UTC](https://discuss.ocaml.org/t/in-core-how-does-the-compare-function-of-keys-affect-the-performance-of-a-hash-table/5661 "2020-05-01T16:18:50Z")
Hi, I’m using the module Hashtbl of Core to create a hash table whose key is of the type Llvm.llvalue. Here is the function Hashtbl.create: let create ?growth\_allowed ?size m = create ~hashable:(Hashable.of\_key m) ?g… --- ## [Can't run example code from the chapter on concurrent programming from RWO](https://discuss.ocaml.org/t/cant-run-example-code-from-the-chapter-on-concurrent-programming-from-rwo/5678)
**Author:** [@ppargc1a](https://discuss.ocaml.org/u/ppargc1a)\ **Replies:** 4\ **Last updated:** [May 1, 2020, 12:23pm UTC](https://discuss.ocaml.org/t/cant-run-example-code-from-the-chapter-on-concurrent-programming-from-rwo/5678 "2020-05-01T12:23:17Z")
I’m reading the chapter on concurrent programming in RWO but I can’t seem to run the example code. I copy pasted it but whenever I try to build with dune build main.exe it always gives this error: Error: Unbound value C… --- ## [When did Core remove polymorphic comparison operators in recent OCaml?](https://discuss.ocaml.org/t/when-did-core-remove-polymorphic-comparison-operators-in-recent-ocaml/5633)
**Author:** [@trungta](https://discuss.ocaml.org/u/trungta)\ **Replies:** 6\ **Last updated:** [April 27, 2020, 5:49pm UTC](https://discuss.ocaml.org/t/when-did-core-remove-polymorphic-comparison-operators-in-recent-ocaml/5633 "2020-04-27T17:49:36Z")
Hi, I’m using the Core library in a project, and recently when I upgraded my OCaml from 4.08.1 to 4.10.0, plenty of compilation errors suddenly appear for comparison expressions like: if (xs = \[\]) then ... or if (x … --- ## [Functorial vs "comparator" container interfaces?](https://discuss.ocaml.org/t/functorial-vs-comparator-container-interfaces/5384)
**Author:** [@jjb](https://discuss.ocaml.org/u/jjb)\ **Replies:** 12\ **Last updated:** [April 16, 2020, 11:05am UTC](https://discuss.ocaml.org/t/functorial-vs-comparator-container-interfaces/5384 "2020-04-16T11:05:36Z")
I wonder if there has been any performance evaluation, of e.g. Set and Map, that compares the functorial (Stdlib Make functor style) versus “comparator” (Base-style) interfaces? To be concrete, suppose we define a Make f… --- ## [Why is the Command module part of Core/Core\_Kernel and not Base](https://discuss.ocaml.org/t/why-is-the-command-module-part-of-core-core-kernel-and-not-base/5111)
**Author:** [@gainhad](https://discuss.ocaml.org/u/gainhad)\ **Replies:** 2\ **Last updated:** [February 3, 2020, 1:22am UTC](https://discuss.ocaml.org/t/why-is-the-command-module-part-of-core-core-kernel-and-not-base/5111 "2020-02-03T01:22:59Z")
Out of curiosity, does anyone know why the Command module is part of Core\_Kernel and not Base? It seems like something really nice to have in Base, and is often the only reason I have to pull in Core or Core\_Kernel inste… --- ## [Upcoming breaking change in Base/Core v0.14](https://discuss.ocaml.org/t/upcoming-breaking-change-in-base-core-v0-14/4806)
**Author:** [@bcc32](https://discuss.ocaml.org/u/bcc32)\ **Replies:** 2\ **Last updated:** [December 3, 2019, 2:04pm UTC](https://discuss.ocaml.org/t/upcoming-breaking-change-in-base-core-v0-14/4806 "2019-12-03T14:04:36Z")
We’re changing functions in Base that used to use the polymorphic variant type \[ \`Fst of 'a | \`Snd of 'b \] to use ('a, 'b) Either.t instead. As well as enabling the use of all of the functions in the Either module, t… --- ## [How to get code completion in spacemacs for OCaml Jane Street Core library?](https://discuss.ocaml.org/t/how-to-get-code-completion-in-spacemacs-for-ocaml-jane-street-core-library/4464)
**Author:** [@abhi18av](https://discuss.ocaml.org/u/abhi18av)\ **Replies:** 5\ **Last updated:** [October 1, 2019, 6:24am UTC](https://discuss.ocaml.org/t/how-to-get-code-completion-in-spacemacs-for-ocaml-jane-street-core-library/4464 "2019-10-01T06:24:10Z")
Hello everyone, I’m a beginner with OCaml and am making my way through the wonderful RealWorldOCaml book. I’m using Emacs via Spacemacs flavor and I like the simplicity of the interface as opposed to an IDE. However, I… --- ## [Destructive substitution: is it possible to replace a type constructor with a monomorphic type?](https://discuss.ocaml.org/t/destructive-substitution-is-it-possible-to-replace-a-type-constructor-with-a-monomorphic-type/1830)
**Author:** [@smolkaj](https://discuss.ocaml.org/u/smolkaj)\ **Replies:** 4\ **Last updated:** [July 30, 2019, 10:05am UTC](https://discuss.ocaml.org/t/destructive-substitution-is-it-possible-to-replace-a-type-constructor-with-a-monomorphic-type/1830 "2019-07-30T10:05:01Z")
I have often wanted something like the following: open Core (\* K.t -\> V.t \*) type t = (K.t, V.t, K.comparator\_witness) Map.t include Map.Make(K) Unfortunately, the include statement fails because Map.Make(K) defines t… --- ## [Performance of \`Printf.sprintf\`](https://discuss.ocaml.org/t/performance-of-printf-sprintf/3936)
**Author:** [@tcoopman](https://discuss.ocaml.org/u/tcoopman)\ **Replies:** 10\ **Last updated:** [June 17, 2019, 7:31pm UTC](https://discuss.ocaml.org/t/performance-of-printf-sprintf/3936 "2019-06-17T19:31:06Z")
With core\_bench I’ve discovered a hot path in my code, namely formatting a date to string was rather slow with Calendar (https://github.com/ocaml-community/calendar/issues/24). Then I went searching for some faster imple… --- ## [How to specialize \`Core.Map\` to a \`Map (K) (V)\` functor?](https://discuss.ocaml.org/t/how-to-specialize-core-map-to-a-map-k-v-functor/3876)
**Author:** [@Saswat\_Padhi](https://discuss.ocaml.org/u/Saswat_Padhi)\ **Replies:** 4\ **Last updated:** [June 1, 2019, 11:24pm UTC](https://discuss.ocaml.org/t/how-to-specialize-core-map-to-a-map-k-v-functor/3876 "2019-06-01T23:24:51Z")
Hello, I understand that a Core.Map is polymorphic over the value type: # module S = Map.Make (String) ;; # let s\_int = S.add\_exn S.empty ~key:"0" ~data:0 ;; # let s\_str = S.add\_exn S.empty ~key:"0" ~data:"zero" ;; Ho… [Next page](https://discuss.ocaml.org/tag/core/61.md?match_all_tags=true&page=1&tags%5B%5D=core)