Yikes, editing race-conditions. I'll fork this off into a different reply.
I presumed that without "USE: io" that "Hello World" was not being sent to the standard output
Actually, that line's like an import statement in Haskell. I would say it's like load in Arc, but that's not really true; USE: and import have to do with module systems, which Arc doesn't have. If you're already familiar with modules, you can skip this stupid explanation, but...
Basically, modules let you structure your functions into different places so that they don't mess with each other. As a silly example, maybe you write a text adventure in Arc and name a function get, as in (get 'ye-flask). But Arc already defines a function called get, as in (map (get 'a) list-of-hash-tables). You want to be able to use both of them at the same time, but would rather not rename your new function. If Arc had modules, you could qualify the function name with the name of the module in which it's defined. Something like
But when you don't want to use Arc's get, you could still overwrite it with the text adventure's get and not need to prefix it with the module name.
This is a vast oversimplification, of course, but that's essentially what they do. So, in languages like Factor, all the I/O routines are in a module called "io". In the io library is a function called print. If you don't need to print things, you don't need to USE: io, which helps keep the "surface area" of your code small.
i.e. With arc I could load/run a file/script with (pr "Hello World") and it would output "Hello World", but with Factor?...
Because Arc doesn't separate anything into modules, you don't need to import things like pr since it's already there by default. The reason the Haskell code in my other reply could do without the import is that putStrLn is similarly defined in Haskell by default: it's in the so-called "standard prelude". That's what the Prelude> prompt tells you in GHCi. You can import other libraries in GHCi, and the prompt will tell you what you're using:
