'file' is just a symbol to represent the single argument taken by the OpenAsReadOnly function, when you call this function with valid argument data (a filename string), the symbol 'file' now points to that string wherever it is referenced in that function.
I'm not too good at explaining things, but perhaps this will help:
http://www.bookshelf.jp/texi/onlisp/onlisp_3.html#SEC14It is written for Common LISP, but the logic still applies.
Lee
