The release of OCaml 5.0.0 is drawing near.
The standard library has been stabilized and many opam packages already
work with this release.
After two alpha releases, we have released the first beta version to help you update your software and libraries ahead of the release (see below for the installation instructions).
If you find any bugs, please report them on GitHub issues.
Compared to the last alpha release, this beta contains many small, internal
runtime fixes (in particular in the
At the user level, the interface of the Domain and Effect module has been tweaked to be (hopefully) more forward-compatible:
- Exceptions related to effects are now defined in the Effecŧ module.
- The value
Domain.recommended_domain_count is no longer a constant and the function
Domain.at_each_spawn has been removed.
With those changes, the standard library should be stable now.
If you are interested in the ongoing list of bug fixes, the
updated change log for OCaml 5.0.0 is available on GitHub.
You can also follow the state of the opam ecosystem on this
opam-repository issues, and at check.ocamllabs.io
A short summary of the changes since the last alpha release is also available
The base compiler can be installed as an opam switch with the following commands
on opam 2.1:
opam switch create 5.0.0~beta1
For previous versions of opam, the switch creation command line is slightly more verbose:
opam switch create 5.0.0~beta1 --repositories=default,beta=git+https://github.com/ocaml/ocaml-beta-repository.git
It might also be interesting to check the new support for parallelism by installing
domainslib library with
opam install domainslib
The source code for the beta release is also available at these addresses:
Fine-Tuned Compiler Configuration
If you want to tweak the configuration of the compiler, you can switch to the option variant with:
opam switch create <switch_name> ocaml-variants.5.0.0~beta1+options <option_list>
option_list is a comma-separated list of
ocaml-option-* packages. For instance, for a
opam switch create 5.0.0~beta1+flambda+nffa ocaml-variants.5.0.0~beta1+options ocaml-option-flambda ocaml-option-no-flat-float-array
The command line above is slightly more complicated for opam versions before 2.1:
opam switch create <switch_name> --packages=ocaml-variants.5.0.0~beta1+options,<option_list> --repositories=default,beta=git+https://github.com/ocaml/ocaml-beta-repository.git
In both cases, all available options can be listed with
opam search ocaml-option.
Optional opam Alpha Repository
During the beta release, if your dependencies are not yet compatible with OCaml 5.0.0,
you might want to check the alpha opam repository: https://github.com/kit-ty-kate/opam-alpha-repository.
Which can be installed with
opam repo add alpha git+https://github.com/kit-ty-kate/opam-alpha-repository.git
You can check that the alpha repository has been correctly installed with
$ opam repo
<><> Repository configuration forswitch<><><><><><><><><><><><><>
This alpha repository contains various fixes that are in the process of being upstreamed,
but it should be less and less required with the progress of the beta release.
See full changelog
Changes Since Last Alpha Release
- #11309, #11424, #11427, +#11545: Add Domain.recommended_domain_count.
(Christiano Haesbaert, Konstantin Belousov, review by David Allsopp,
KC Sivaramakrishnan, Gabriel Scherer, Nicolas Ojeda Bar)
#11423: Move the effect exceptions to the Effect module
(KC Sivaramakrishnan, Xavier Leroy, Florian Angeletti, review by
Florian Angeletti, Xavier Leroy, and KC Sivaramakrishnan)
#11593: Remove Domain.at_each_spawn
(Florian Angeletti, review by Guillaume Munch-Maccagnoni
and KC Sivaramakrishnan)
#11303: Ensure that GC is not invoked from bounds check failures
(Stephen Dolan, review by Sadiq Jaffer and Xavier Leroy)
#5299, #4787, #11138, #11272, #11506: To help debugging,
now dynamically checks that the domain lock is held and fails
otherwise (with a fatal error at most entry points of the C API, or
systematically in debug mode). A new variable
introduced and is
NULL when the domain lock is not held. This
allows to test from C code if the current thread holds its domain lock.
(Guillaume Munch-Maccagnoni, review by Florian Angeletti, Damien
Doligez, Sadiq Jaffer, Xavier Leroy, and Gabriel Scherer)
#11223: The serialisation format of custom blocks changed in 4.08,
but the deserialiser would still support the pre-4.08 format. OCaml
5.x removed support for this old format and provided a clear error message
in this case.
(Hugo Heuzard, review by Gabriel Scherer)
#11504, #11522: Use static allocation for
no-flat-float-array mode, it's more efficient and avoids a race condition
(Xavier Leroy, report by Guillaume Munch-Maccagnoni, review by David Allsopp)
#11461, #11466: Fix
gethostbyaddr for IPv6 arguments and make it domain-safe
(Olivier Nicole, Nicolás Ojeda Bär, David Allsopp and Xavier Leroy,
review by the same)
#11479: Make Unix.symlink domain-safe on Windows
(Olivier Nicole, review by Xavier Leroy and David Allsopp)
#11294: Switch minimum required autoconf to 2.71.
(David Allsopp, review by Xavier Leroy)
#11370, #11373: Don't pass CFLAGS to flexlink during configure.
(David Allsopp, report by William Hu, review by Xavier Leroy and
#11487: Thwart FMA test optimization during configure
(William Hu, review by David Allsopp and Sébastien Hinderer)
#11468: Fix regression from #10186 (OCaml 4.13) detecting IPv6 on Windows for
mingw-w64 i686 port.
(David Allsopp, review by Xavier Leroy and Sébastien Hinderer)
#11482, #11542: Fix random crash in large closure allocation
(Damien Doligez, report by Thierry Martinez and Vincent Laviron, review by
#11508, #11509: make Bytes.escaped domain-safe
(Christiano Haesbaert and Gabriel Scherer,
review by Xavier Leroy,
report by Jan Midtgaard and Tom Kelly)
#11516, #11524: Fix the
(Chris Casinghino, review by Nicolás Ojeda Bär and Florian Angeletti)
#11576: Fix bug in Bigarray.Genarray.init in the the case of zero-dimensional
(Nicolás Ojeda Bär, Jeremy Yallop, report by Masayuki Takeda, review by Jeremy
Yallop and Florian Angeletti)
#11587: Prevent integer comparison from being used on pointers
(Vincent Laviron, review by Gabriel Scherer)
- #11093: Add tutorials on parallelism features and the relaxed memory model
(KC Sivaramakrishnan, review by Damien Doligez, Anil Madhavapeddy, Gabriel
Scherer, Thomas Leonard, Tom Ridge, Xavier Leroy, Luc Maranget, Fabrice
Buoro, Olivier Nicole, Guillaume Munch-Maccagnoni, Jacques-Henri Jourdan)