Question

If I compile the following module into a dll

namespace MyNs
module SomeModule =
    do printfn "module loading"
    let x = 23

then reference the dll in FSI and execute the command open MyNs.SomeModule “module loading” does not print immediately. It only prints when I access x which causes all the top level let and do bindings to execute (normal behavior I know in the .NET world). Is there any way, perhaps via an attribute on the module, I can indicate that module should load immediately upon opening in FSI?

Answer 1

Opening a module never does anything at runtime. It just puts all the symbols in the opened namespace in scope for unqualified access below the open statement.

Section 12.5 of the language spec is what you want to read – this details when the static initialization of a module will run.

Given that, the only time when this initialization is run automatically, as far as I know, is for last module in an exe.

I.e. I don’t think there is a direct way to accomplish what you want.

If you have reflective access to the module:

ModuleType.TypeInitializer.Invoke(null, null)

will invoke the static initialization.