code: def p_if_else(p):
      
      cond_ = p[1]
      then_ = p[3]
      else_ = p[4][0]
      endif = p[4][1]
      p[0] = make_sentence('IF', cond_, then_, make_block(else_, endif), lineno=p.lineno(2))
docs: statement : if_then_part NEWLINE program_co else_part