I was going to say...

  (def if-with-do (expr)
    (and (caris expr 'if)
         (some [caris _ 'do] expr)))

  (def accum-expr (accumf testf exprs)
    (map [ontree (andf testf accumf) _] exprs))

  (def keep-expr (testf exprs)
    (accum a (accum-expr a testf exprs)))

  (def count-expr (testf exprs)
    (summing s (accum-expr s testf exprs)))

  (defs count-ifs-with-do (exprs) (count-expr if-with-do exprs)
        count-ifs         (exprs) (count-expr [caris _ 'if] exprs)
        ifs-with-do       (exprs) (keep-expr if-with-do exprs)
        ifs               (exprs) (keep-expr [caris _ 'if] exprs))

  arc> (each file '("arc.arc"
                    "strings.arc"
                    "pprint.arc"
                    "code.arc"
                    "html.arc"
                    "srv.arc"
                    "app.arc"
                    "prompt.arc")
         (prn "=== " file)
         (let exprs (readfile file)
           (prn (count-ifs-with-do exprs) "/" (count-ifs exprs))))
  === arc.arc
  11/120
  === strings.arc
  3/18
  === pprint.arc
  5/5
  === code.arc
  0/0
  === html.arc
  4/24
  === srv.arc
  4/21
  === app.arc
  9/53
  === prompt.arc
  2/6