commander-s/scheme/config.scm

(define *configuration* '())

(define (init-config config-file)
  (with-input-from-file 
   config-file
   (set! *configuration* (read))))

(define (read-config config-file)
  (call-with-input-file config-file read))

(define (config-file-to-use)
  (let ((from-env (getenv "CMDRSRC"))
	(default-location
	  (string-append (home-dir) "/.cmdrsrc")))
    (if (and from-env (file-exists? from-env))
	from-env
	default-location)))

(define (read-config-file!)
  (with-errno-handler
   ((errno data)
    (else #f))
   (let ((conf-file (config-file-to-use)))
     (for-each
      (lambda (option.value)
	(cond
	 ((and (pair? option.value)
	       (pair? (car option.value))
	       (symbol? (caar option.value))
	       (symbol? (cdar option.value))
	       (assoc (car option.value) *configuration*))
	  => (lambda (p)
	       (set-cdr! p (cdr option.value))))
	 (else
	  (error "Unknown option value or ill-formed option" 
		 option.value conf-file))))
      (read-config conf-file)))))

(define (config module option)
  (let ((probe (assoc (cons module option) *configuration*)))
    (if probe 
        (cdr probe)
        (error "unknown configuration option" option))))

(define (define-option module option-name default-value)
  (set! *configuration*
	(cons (cons (cons module option-name) default-value)
	      *configuration*)))