Icon code for positive-edge triggered bistable multivibrator

bistable.icn

procedure co_bistable(off_state, on_state)
   local button, bistable_button, bistable_state
   /off_state := "off"
   /on_state  := "on"
   bistable_button := bistable_state := button := off_state
   return create while button := ( 
         if button ~== bistable_button
            then if (bistable_button := button) == on_state 
               then  bistable_state := if bistable_state == off_state 
                  then on_state
                  else off_state
               else &null
            else &null
      ,  bistable_state
      ) @ &source
end

procedure main()
   local bistable, i
   bistable := co_bistable("no","yes")
   
   every i := 1 to 30 do {
      if 1 = ?2 
         then write("  button -> off yields state   ", "no"   @ bistable)
         else write("button -> ON    yields state ",   "yes"  @ bistable)
      }
end