code: def p_ifdef(p):
      
      global ENABLED
  
      if ENABLED:
          p[0] = [p[2]] + p[3]
          p[0] += ['#line %i "%s"' % (p.lineno(4) + 1, CURRENT_FILE[-1])]
      else:
          p[0] = ['#line %i "%s"' % (p.lineno(4) + 1, CURRENT_FILE[-1])]
  
      ENABLED = IFDEFS[-1][0]
      IFDEFS.pop()
docs: ifdef : if_header NEWLINE program ENDIF