Hello, I’ve just installed the ocaml dev environment on a windows 11 system, using opam 2.2.
Trying the hello world example using Dune i found that on first run, the executable takes more than 20 secs to start. Successive run starts immediately.
I remember that utop did the same thing on first run. Any hints?
That sounds like Windows Defender or some other malware/anti-virus checker on your machine doing a scan. If it is, eventually it will get worse; you will start running into your executables randomly being deleted. Try adding a folder exclusion to your development directory (ex. C:\source) in Defender/Norton/whatever you have; Add an exclusion to Windows Security - Microsoft Support (edit) has instructions for Defender.
@jbeckford That page 404s for me.
The link is fixed. Thanks!
Thank you, I’m running Avira AV, excuded the project folder and the problem seems to be solved.
Do you think I have to exclude some other folder or file?
You should add the opam root folder as well. Run:
opam var root
to show the folder.
Done, just one more question,
Should I rerun “opam init” to use different shell (PowerShell, Win11 prompt, cygwin)?
PS: Have a nice Halloween night 
The opam init is independent of the shell, except perhaps under Cygwin. (Someone from the opam team will need to answer that)
I typically use PowerShell inside Windows Terminal or inside Visual Studio Code for OCaml development. That makes it easy to copy and paste commands from Unix-oriented sites … without having to translate / into \, etc.
Ok, thanks again I’m going to install and configure VSCode in the evening, ITA time.