The stabilisation of OCaml 5.0 has been progressing well during the last month.
We have thus released a first normal alpha release of OCaml 5.0.0 to help
fellow hackers join us early in our bug hunting and opam ecosystem fixing fun
(see below for the installation instructions).
You can follow the progress in stabilising the opam ecosystem on
If you find any bugs, please report them here:
Compared to the zeroth alpha release, this alpha release restores the support
for the bytecode debugger, and integrates a change of type in the FFI API that
might trigger some warnings in FFI code.
We also have a change in the installed files: the compiler distributes now its
own META files rather than relying on either findlib or dune to provide those
files. This should simplify the tasks of both tools in future version.
Note there are still some changes expected in the Effect module before the next
candidate release. Generally, both the Effect and Domain modules are still
experimental and might change API even during the beta releases.
If you are interested by the ongoing list of bug fixes, the
updated change log for OCaml 5.0.0 is available at:
A short summary of the changes since the zeroth alpha release is also available
The base compiler can be installed as an opam switch with the following commands
on opam 2.1:
opam update opam switch create 5.0.0~alpha1
For previous version of opam, the switch creation command line is slightly more verbose:
opam update opam switch create 5.0.0~alpha1 --repositories=default,beta=git+https://github.com/ocaml/ocaml-beta-repository.git
If you want to test this version, it is strongly advised to install the alpha
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 for switch 5.0.0~alpha1 <><><><><><><><><><><><><> 1 alpha git+https://github.com/kit-ty-kate/opam-alpha-repository.git 2 default https://opam.ocaml.org
This alpha repository contains various fixes in the process of being upstreamed which
vastly increases the number of opam packages currently compatible with OCaml 5.0.0 .
If you want to tweak the configuration of the compiler, you can switch to the option variant with:
opam update opam switch create <switch_name> ocaml-variants.5.0.0~alpha1+options <option_list>
option_list is a comma separated list of
ocaml-option-* packages. For instance, for a flambda and no-flat-float-array switch:
opam switch create 5.0.0~alpha1+flambda+nffa ocaml-variants.5.0.0~alpha1+options ocaml-option-flambda ocaml-option-no-flat-float-array
The command line above is slightly more complicated for opam version anterior to 2.1:
opam update opam switch create <switch_name> --packages=ocaml-variants.5.0.0~alpha1+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.
The source code for the alpha is also available at these addresses:
#11400: Runtime events counters fixes
Fixes mismatch between OCaml and C APIs, removes events from 4.x that
are not present in the 5.0 GC and adds some missing probes.
(Sadiq Jaffer, review by Gabriel Scherer, Florian Angeletti)
#11368: Runtime events buffer size OCAMLRUNPARAMS fix
The runtime events buffer size can now be set via the ‘e’ OCAMLRUNPARAM.
This is previously mistakenly enabled/disabled tracing instead.
(Sadiq Jaffer, review by KC Sivaramakrishnan, David Allsopp, Damien Doligez)
#11304: Fix data race on Windows file descriptors
(Olivier Nicole and Xavier Leroy, review by Xavier Leroy, David Allsopp,
and Sadiq Jaffer)
- (breaking change) #11337: pass ‘flags’ metadata to root scanners, to optimize stack
scanning in the bytecode interpreter.
Changes the interface of user-provided root-scanning hooks.
(Gabriel Scherer, review by Xavier Leroy,
Guillaume Munch-Maccagnoni, Sadiq Jaffer and Tom Kelly)
#11144: Restore frame-pointers support for amd64
(Fabrice Buoro, review by Frederic Bour and KC Sivaramakrishnan)
- (breaking change) #11255: in the C interface,
&Field(v, i)now has type
volatile value *
value *in OCaml 4. This makes the memory model
for mixed OCaml/C code better defined, but can cause warnings or type
errors in user C code.
(KC Sivaramakrishnan, review by Xavier Leroy, Gabriel Scherer and
Guillaume Munch-Maccagnoni, additional discussions with Stephen
Dolan and Luc Maranget)
#10867, +#11345: Remove deprecated values:
…, the infix operator (.[ ]<-).
(Nicolás Ojeda Bär, review by Damien Doligez)
#11309, #11424, #11427: Add Domain.recommended_domain_count.
(Christiano Haesbaert, Konstantin Belousov, review by David Allsopp,
KC Sivaramakrishnan, Gabriel Scherer, Nicolas Ojeda Bar)
#11065: Port the bytecode debugger to 5.0, adding support for effect handlers.
(Damien Doligez and fabbing, review by fabbing and Xavier Leroy)
#11382: OCamlmktop use a new initialization module “OCamlmktop_init” to
preserve backward-compatibility with user-module provided modules that install
(Florian Angeletti, review by Gabriel Scherer and David Allsopp)
#11007, #11399: META files for the stdlib, compiler-libs and other libraries
(unix, dynlink, str, runtime_events, threads, ocamldoc) are now installed
along with the compiler.
(David Allsopp, Florian Angeletti, Nicolás Ojeda Bär and Sébastien Hinderer,
review by Daniel Bünzli, Kate Deplaix, Anil Madhavapeddy and Gabriel Scherer)
#10790: don’t drop variance and injectivity annotations when pretty printing
withconstraints (for example,
with type +!'a t = ...).
(Florian Angeletti, report by Luke Maurer, review by Matthew Ryan and
#11387, module type with constraints no longer crash the compiler in presence
of both shadowing warnings and the
(Florian Angeletti, report by Christophe Raffalli, review by Gabriel Scherer)