F# does type inference like this:

    let x = 1;

x is now an integer. Now you can't do

    printfn "%s" x;

Only

    printfn "%i" x;

So it has strong static typing, but most of the time you don't need to be explicit about them. It can even infer function types.

If you use FSI (F# interactive( it will always print the signatures in between, so that it's really easy to explore interfaces.