Common Lisp函数是否返回3个值？

Question

任何Common Lisp(内置)函数是否返回超过2个值？我知道许多人返回2,但我想不到一个返回3.

(我在这里看到关于返回超过2个值的评论,并试图想到CL做到这一点的情况,但不能.)

Answer 1

是的,存在这样的功能.以下是COMMON-LISP包中的完整函数列表,它们返回三个值,如SBCL源代码中所声明的:

COMPILE                                 required: 3, optional: 0, rest?: NIL
INTEGER-DECODE-FLOAT                    required: 3, optional: 0, rest?: NIL
COMPILE-FILE                            required: 3, optional: 0, rest?: NIL
GET-PROPERTIES                          required: 3, optional: 0, rest?: NIL
FUNCTION-LAMBDA-EXPRESSION              required: 3, optional: 0, rest?: NIL
DECODE-FLOAT                            required: 3, optional: 0, rest?: NIL
RENAME-FILE                             required: 3, optional: 0, rest?: NIL

此外,以下函数返回大于三的常量值:

DECODE-UNIVERSAL-TIME                   required: 9, optional: 0, rest?: NIL
GET-DECODED-TIME                        required: 9, optional: 0, rest?: NIL

这些函数返回可变数量的值,因此可能超过三个:

NO-APPLICABLE-METHOD                    required: 0, optional: 0, rest?: T
NO-NEXT-METHOD                          required: 0, optional: 0, rest?: T
VALUES                                  required: 0, optional: 0, rest?: T

(I've omitted some functions from this list where SBCL does not declare
a values type explicitly.  get-setf-expansion is one of them.)

列的说明:required这些函数的最小返回值optional数,SBCL认为可能返回或可能不返回的固定数量的返回值,rest?表示预期可变数量的值.(仅macroexpand与macroexpand-1实际使用和选购,不要问我为什么.)

只是为了好玩,这里是我用来提出这些表的源代码:

(do-external-symbols (sym :common-lisp)                                         
  (when (fboundp sym)                                                           
    (multiple-value-bind (required optional rest)                               
        (let ((fun-type (sb-int:info :function :type sym)))                     
          (etypecase fun-type                                                   
            (sb-kernel:fun-type                                                 
             (let ((returns                                                     
                    (sb-kernel:fun-type-returns fun-type)))                     
               (etypecase returns                                               
                 (sb-kernel:values-type                                         
                  (values (length (sb-kernel:values-type-required returns))     
                          (length (sb-kernel:values-type-optional returns))     
                          (sb-kernel:values-type-rest returns)))                
                 (sb-kernel:named-type                                          
                  (if (sb-kernel:named-type-name returns)                       
                      (values 1 0 t)                                          
                      (values 0 0 nil))))))                                     
            (t                                                                  
             (values 0 0 t))))                                                  
      (format t                                                                 
              "~A~40Trequired: ~D, optional: ~D, rest?: ~A~%"                   
              sym                                                               
              required optional rest))))

Answer 2

decode-universal-time返回九个值.