Appendix A Recipies

• Calculating the average length of subject-lines

  ;; the average length of all our
  (let ((len 0) (n 0))
    (mu:for-each-message
      (lambda (msg)
        (set! len (+ len (string-length (or (mu:subject msg) ""))))
        (set! n (+ n 1))))
    (if (= n 0) 0 (/ len n)))
    ;; this gives a rational, exact result;
    ;; use exact->inexact to get decimals
    
  ;; we we can make this short with the mu:average (with (mu stats))
  (mu:average (lambda (msg) (string-length (or (mu:subject msg) ""))))