ranking.arc

(= gravity* 1.8 timebase* 120 front-threshold* 1 
   nourl-factor* .4 lightweight-factor* .3 )

(def frontpage-rank (s (o scorefn realscore) (o gravity gravity*))
  (* (/ (let base (- (scorefn s) 1)
          (if (> base 0) (expt base .8) base))
        (expt (/ (+ (item-age s) timebase*) 60) gravity))
     (if (no (in s!type 'story 'poll))  .5
         (blank s!url)                  nourl-factor*
         (lightweight s)                (min lightweight-factor* 
                                             (contro-factor s))
                                        (contro-factor s))))

(def contro-factor (s)
  (aif (check (visible-family nil s) [> _ 20])
       (min 1 (expt (/ (realscore s) it) 2))
       1))

(def realscore (i) (- i!score i!sockvotes))