Something like this maybe:
(use posix)
(define file-separator #f)
(define path-separator #f)
(let ((sysname (let ((si (system-information)))
(if (pair? si)
(car si)
#f))))
(cond
((equal? sysname "windows")
(set! file-separator "\\")
(set! path-separator ";"))
(else
(set! file-separator "/")
(set! path-separator ":"))))
Is it already defined anywhere? I could not find it.