How to correctly add new entity with F# on MonoTouch

How to correctly add new entity with F# on MonoTouch

I would like to know how to correctly add new objects to a CoreData
datastore. The following code works, but I'm a bit surprised that I have
to use new NSString and new NSNumber to set the values. Besides that I'm
afraid that my code would lead to memory leaks.
let ed = NSEntityDescription.InsertNewObjectForEntityForName("Document",
context)
ed.SetValueForKey(new NSString("title"), new NSString("title"))
ed.SetValueForKey(new NSString("file"), new NSString("file"))
ed.SetValueForKey(new NSString("base_name"), new NSString("base_name"))
ed.SetValueForKey(new NSNumber(123), new NSString("question_count"))
ed.SetValueForKey(new NSString("revision"), new NSString("revision"))
ed.SetValueForKey(new NSString("valid"), new NSString("valid"))
let error = context.Save()