task
Essentially, count the number of occurrences of =={{header| on each task page.

Output:

100 doors: 20 examples.
99 Bottles of Beer: 29 examples.
Abstract type: 10 examples.

Total: X examples.
For a full output, updated periodically, see Rosetta Code/Count examples/Full list.

You'll need to use the Media Wiki API, which you can find out about locally, here, or in Media Wiki's API documentation at, API:Query

(load "@lib/http.l")
 
(client "rosettacode.org" 80
   "mw/api.php?action=query&list=categorymembers&cmtitle=Category:Programming_Tasks&cmlimit=500&format=xml"
   (while (from " title=\"")
      (let Task (till "\"")
         (client "rosettacode.org" 80 (pack "wiki/" (replace Task " " "_"))
            (let Cnt 0
               (while (from "<span class=\"tocnumber\">")
                  (unless (sub? "." (till "<" T))
                     (inc 'Cnt) ) )
               (out NIL (prinl (ht:Pack Task) ": " Cnt)) ) ) ) ) )