专注于关键词的通用函数(Generic Function Specializing on Keywords)

编程入门行业动态更新时间:2024-10-24 18:24:36

在Common Lisp中有没有一种方法可以创建一个泛型函数，其中专用于参数的参数是关键字参数？

例如，而不是这个：

CL-USER> (defgeneric tst (a)) #<STANDARD-GENERIC-FUNCTION TST (0)> CL-USER> (defmethod tst ((a list)) (print a)) #<STANDARD-METHOD TST (LIST) {1004ECC903}>

..在参数'a'上指定。我想要有以下几点：

CL-USER> (defgeneric tst (&key a)) #<STANDARD-GENERIC-FUNCTION TST (0)> CL-USER> (defmethod tst (&key (a list)) (print a)) #<STANDARD-METHOD TST (LIST) {1004ECC903}>

显然，这与设置关键字参数的默认值的语法冲突，所以我有点卡住了。在实际的代码中，这个问题与我选择了不同的参数布局有关，所以这不是问题（并且引导起来有点整洁！）但是如果我再遇到这个问题，我想我最好问专家！

欢呼一切

Is there a way in Common Lisp to create a generic function where the argument to specialize on is a keyword argument?

For example rather than this:

CL-USER> (defgeneric tst (a)) #<STANDARD-GENERIC-FUNCTION TST (0)> CL-USER> (defmethod tst ((a list)) (print a)) #<STANDARD-METHOD TST (LIST) {1004ECC903}>

..which specifies on the argument 'a'. I'd like to have the following:

CL-USER> (defgeneric tst (&key a)) #<STANDARD-GENERIC-FUNCTION TST (0)> CL-USER> (defmethod tst (&key (a list)) (print a)) #<STANDARD-METHOD TST (LIST) {1004ECC903}>

Obviously this clashes with the syntax for setting the default values of keyword arguments so I'm a tad stuck. In the actual code this problem relates to I chose a different argument layout so this wasn't an issue (and was a bit tidier to boot!) but in case I run into this again I thought I best ask the experts!

Cheers all