Quelle  back.cob

       identification division.
       program-id. back.
      * von Arthur Watson, arthur@mccabe.com
      * Aufsatz über Essential Complexity
       author. Jens.
       date-written. 17.2.2006.
       date-compiled.
       data division.
       working-storage section.
         78 NULL-POSITION value 7.
         78 back-scroll   value 8.
         77 line-0       pic 9(4).
         77 nlines       pic 9(4).
         77 repaint-flag pic 9(4).
         77 sc-height    pic 9(4).
         77 hit-eof      pic 9(4).
       linkage section.
         77 n          pic 9(4).
         77 pos        pic 9(8).
         77 force      pic 9(4).
         77 only-last  pic 9(4).
       procedure division using n pos
                 force only-last.
         if n > back-scroll then
           move 1 to repaint-flag
         else
           if only-last
             compute repaint-flag =
               (n > sc-height - 1)
           else
             move 0 to repaint-flag
           end-if
         end-if
         move 0 to hit-eof.
         subtract 1 from n.
         perform until n < 0        
           call back-line using pos
           if pos = NULL-POSITION
             if Not force>0 then
               stop run
             end-if
             move 0 to line-0
           end-if
           call add-back-pos using pos
           add 1 to nlines
           if not repaint-flag then
             call home
             call add-line
             call put-line
           end-if
           call eof-check
           if nlines = 0 then
             call eof-bell
           else
             if repaint-flag > 0 then
               call repaint
             end-if
           end-if
           subtract 1 from n
         end-perform
        end-program  back.