On Fri, Mar 11, 2016 at 3:48 PM, Yotam Barnoy <yotambarnoy@gmail.com> wrote:

Another question: how will 4.03 be handled with regard to OPAM? The way I see it, the majority of users will want Flambda activated by default. Companies or individuals that depend on OCaml for their business will probably want to start off with Flambda turned off, and turn it on as needed. Additionally, to get Flambda tested by as many people as possible, I believe we want people to use it by default.

One of the (many) things I think is done right in OPAM is the `opam switch ...` framework, so you can have multiple compilers installed easily and handle them on a simple switching framework.

Operationally, I'd put it on an Ocaml 4.03+flambda and then in point-release .1 or .2 I'd make it the default once it has seen some use by the early adopters, having an ocaml 4.03+no-flambda option for those who are behind on schedule. This would allow people to gracefully roll forward one release, and gracefully roll backward once the switch happens which lessens the strain on a lot of stuff operationally.

The more risky alternative is to just make flambda the default in 4.03 and have a no-flambda option for those in the know, but this risks introducing regressions at a greater extent and should be balanced by the knowledge of how stable flambda has proven to be. If, for instance, it has seen major use inside Janes St. for some time and has been generally stable, this is a far more viable option.