For example, see SLIB, the portable Scheme library http://www-swiss.ai.mit.edu/~jaffer/SLIB.html . It is designed to work with R5RS Scheme and before, thus it can't use any module systems. Instead, it uses a naming convention, which works pretty well. The problem is that, to make it work, all programmer should agree and follow the convention. The so-called module systems make it easier to follow the rules by making the existence of the convention invisible (automatically adding prefixes effectively, e.g.) or preventing programmers from doing things differently.

In Scheme, traditionally such matter has been settled by "agreed to disagree"---instead of choosing one, the spec just leave it unspecified. But R6RS had a goal to allow portable libraries, so it had to choose one; for modules, it is better to have lesser but one module system, rather than having multiple ("better" in various regards) or than having none.

In Arc, ultimately it's up to pg.

I also wanted to mention a fourth benefit that I think modules can offer, which is:

4. They allow some form of management of dependencies between pieces of code.

  MyStuff = (function(){
    var modulevar;
    function innerfunction(){...}
    function exportedfn(){...}
    return {exportedfn: exportedfn}})();

  (= MyModule
    (let (modulevar innerfunction exportedfn) nil
         (def innerfunction () ...)
         (def exportedfn () ...)
         (fill-table (table) 'exportedfn exportedfn)))

  (module MyModule
    (module-var modulevar)
    (public exportedfn)
    (def innerfunction () ...)
    (def exportedfn () ...))

"The kind of modularity provided by packages is actually a bit odd. We have modules not of objects, but of names. Every package that uses 'common-lisp' has access to the name 'cons', because 'common-lisp' includes a function with that name. But in consequence a variable called 'cons' would also be visible in every package that used 'common-lisp'. If packages are confusing, this is the main reason why; they're not based on objects, but on their names".

  (mac def-with-prefix (prefix name args . body)
    `(eval (list 'def
            (read (+ (coerce ,prefix 'string)
                     "-"
                     (coerce ',name 'string)))
            ,args
            ,@body)))

  (= prefix 'blub)
  (def-with-prefix prefix foo (x) (+ 1 x))

  (def blub-foo (x) (+ 1 x)))

  (mac def-with-prefix (prefix name args . body)
    `(def
        (read (+ (coerce ,prefix 'string)
                 "-"
                 (coerce ',name 'string)))
        ,args
        ,@body))

  (def-with-prefix 'blub 'foo (x) (+ 1 x))

  (def (read (+ ...blah...blah...)) (x) (+ 1 x))

    `(def ,(read (+ (coerce prefix 'string) "-" (coerce name 'string))) ,args ,@body)

  (= pre 'blub)

  (your-def-with-prefix pre foo (x) (+ 1 x))
  => #<procedure: pre-foo>

  (my-def-with-prefix pre foo (x) (+ 1 x))
  => #<procedure: blub-foo>

  `(def ,(read (+ (coerce (eval prefix) 'string) "-" (coerce name 'string))) ,args ,@body)

  (let pre2 'blub (your-def-with-prefix pre2 foo (x) (+ 1 x)))
  => Error: "reference to undefined identifier: _pre2"

cchooper, did you actually ever run your version? I can't make your orginal version work.

  arc> (def-with-prefix pre foo (x) (+ 1 x))
  Error: "reference to undefined identifier: _x"

  arc> (macex '(def-with-prefix pre foo (x) (+ 1 x)))
  (eval (list (quote def) ; my indentation
              (read (+ (coerce pre (quote string)) "-" (coerce (quote foo) (quote string))))
              (x) (+ 1 x)))

  (mac def-with-prefix (prefix name args . body)
    `(eval (list 'def
            (read (+ (coerce ,prefix 'string)
                     "-"
                     (coerce ',name 'string)))
            ',args
            ,@(map [list 'quote _] body))))

Here's a slightly less clunky version:

  (mac def-with-prefix (prefix name args . body)
    `(eval (join (list 'def 
                  (sym (+ (coerce ,prefix 'string)
                          "-"
                          (coerce ',name 'string)))
                  ',args)
            ',body)))

In Arc:

  arc> (= foo 's)
  s
  arc> (set foo 4)
  4
  arc> foo
  4
  arc> s
  Error: "reference to undefined identifier: _s"

  CL-USER> (setf foo 's)
  S
  CL-USER> (set foo 4)
  4
  CL-USER> foo
  S
  CL-USER> s
  4

http://arclanguage.org/item?id=3315