code: def type_of_line(line):
      
  
      if line_is_comment(line):
          return "comment"
      elif line_is_executable(line):
          return "exec_stmt"
      elif line_is_pgm_unit_end(line):
          return "pgm_unit_end"
      else:
          if line_is_pgm_unit_start(line):
              return "pgm_unit_start"
          else:
              return "other"
docs: Given a line of code, type_of_line() returns a string indicating
         what kind of code it is.