[R] Changing the value of variables passed to functions as arguments

[Paul Baer]

Is it possible to write functions in such a way that, rather than 
having to write "a=function(a)", one can just write "function(a)" and 
have the variable passed as the argument be modified?

My real interest here is being able to invoke the editor by writing 
"ed(filename)" rather than filename=edit(filename).

Thanks,

--Paul