Using a package before it is #require'd will result in unbound module errors even after it is later #require'd.

[ciaran16]

For example, Core.Std.printf "Hello world" results in Error: Unbound module Core as expected. However if I then do #require "core.top" and then rerun the above, I still get Unbound module Core.

If I restart iocaml and make sure to #require a package first, then it works fine.

[andrewray]

That is something I have seen before. There was some logic I didn't get working (related to something like Btype.snap or somesuch) which might be related.

FWIW rather than restart iocaml, you can just restart the kernel with 'ctrl+m .'