Dear OCaml users, 

Five months after the initial merge of the multicore branch into the mainline 
OCaml and three months after the release of OCaml 4.14.0, OCaml 5.0.0 is 
starting to take shape. 

I am thus happy to announce an exceptional zeroth alpha release of 
OCaml 5.0.0 (see below for the installation instructions). 

This alpha release is expected to be rougher than an usual alpha release, 
due to the full rewrite of the OCaml runtime. In particular, the bytecode 
debugger will only be available in the next alpha release. Similarly, there 
will be some changes to the internal C runtime API and to the files installed 
by the compiler package in the next alpha release. 

Moreover, this zeroth alpha release is the occasion to remind everyone that 
OCaml 5.0 itself is expected to be a more experimental release than usual. 
Notably, the native compiler will only be available on the ARM64 and 
x86-64 architectures in this 5.0 release. 

Nevertheless, this zeroth alpha version is already stable enough for fellow 
hackers eager to join us in our early bug hunting and opam ecosystem fixing fun, 
or to venture in the new era of parallelism and (experimental) effects. 

You can follow the progresses in stabilising the opam ecosystem on 

https://github.com/ocaml/opam-repository/issues/21526 

A brief summary is that at least dune, merlin, ppxlib, utop, ocamlfind, 
and ocamlbuild work (potentially by using patches from the 
alpha opam repository). 

If you find any bugs, please report them here: 

https://github.com/ocaml/ocaml/issues 

In particular, any sequential OCaml 4 library or program should be valid in 
OCaml 5 (except for deprecated modules and functions). Please don't hesitate 
to report any forward-compatibility bugs! 

If you are interested by the ongoing list of bug fixes, the 
updated change log for OCaml 5.0.0 is available at: 

https://github.com/ocaml/ocaml/blob/5.0/Changes 

Happy hacking, 
Florian Angeletti for the OCaml team. 

Installation instructions 
------------------------- 
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~alpha0 

For previous version of opam, the switch creation command line is slightly more verbose: 

opam update 
opam switch create 5.0.0~alpha0 --repositories=default,beta=git+https://github.com/ocaml/ocaml-beta-repository.git 

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~alpha0+options <option_list> 

where <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~alpha0+flambda+nffa ocaml-variants.5.0.0~alpha0+options ocaml-option-flambda ocaml-option-no-flat-float-array 

The command line above is slightly more complicated for an opam version anterior to opam 2.1: 

opam update 
opam switch create <switch_name> --packages=ocaml-variants.5.0.0~alpha0+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". 

If you want to test this version, it is strongly advised to install the alpha 
opam repository 

https://github.com/kit-ty-kate/opam-alpha-repository 

with 

opam repo add alpha git://github.com/kit-ty-kate/opam-alpha-repository.git 

This alpha repository contains various fixes in the process of being upstreamed. 

The source code for the alpha is also available at these addresses: 

https://github.com/ocaml/ocaml/archive/5.0.0-alpha0.tar.gz 
https://caml.inria.fr/pub/distrib/ocaml-5.0/ocaml-5.0.0~alpha0.tar.gz