Lisp宏多任务

Question

我有一个关于lisp宏的问题。我想检查一个条件，如果它是真的，运行几个东西，而不是只运行一个。对于错误的方式也是如此。有人能帮帮忙吗？？

(defmacro test (condition (&rest then) (&rest else))
  `(if ,condition (progn ,@then) (progn ,@else)))

(test (= 4 3)
      (print "YES") (print "TRUE")
      (print "NO") (print "FALSE"))

Answer 1

测试宏的常用方法是使用macroexpand。

您的测试用例缺少括号(lisp阅读器不关心空格，如换行符和缩进)：

(macroexpand '(test (= 4 3)
                    (print "YES") (print "TRUE")
                    (print "NO") (print "FALSE")))
  Error while parsing arguments to DEFMACRO TEST:
    too many elements in
      ((= 4 3) (PRINT "YES") (PRINT "TRUE") (PRINT "NO") (PRINT "FALSE"))
    to satisfy lambda list
      (CONDITION (&REST THEN) (&REST ELSE)):
    exactly 3 expected, but got 5

而

(macroexpand '(test (= 4 3)
                    ((print "YES") (print "TRUE"))
                    ((print "NO") (print "FALSE"))))
(IF (= 4 3)
    (PROGN (PRINT "YES") (PRINT "TRUE"))
    (PROGN (PRINT "NO") (PRINT "FALSE")))

请注意，CL有cond，通常在if子句中需要多种形式时使用。