[unstruktured]

There is absolutely no reason to use double semicolons in practice. The only place you really should see it is when using the repl.

[sigzero]

Yeah, it makes me think he doesn't understand them in OCaml.

[acjohnson55]

I worked in OCaml for a year and I couldn't tell you by memory what the difference was. I remember being very annoyed by OCaml's many language quirks.