Lisp:使用语法糖访问递归哈希 [英] Lisp: Accessing recursive hashes with syntactic sugar

问题描述

我正在尝试构建一个函数(或宏)，以简化哈希表深处的数据的获取和设置(意思是哈希内的哈希，哈希内的哈希等).我不认为我可以使用宏来实现，而且我不确定如何使用eval来实现.我希望能够执行以下操作:

I'm trying to build a function (or macro) to ease the getting and setting of data deep in a hash table (meaning, a hash within a hash, within a hash, etc). I don't think I can do it with a macro, and I'm not sure how to do it with eval. I'd like to be able to do the following:

(gethashdeep *HEROES* "Avengers" "Retired" "Tony Stark")

并返回钢铁侠"

所有哈希都是用以下方式创建的:

The hashes are all created with:

(setf hashtablename (make-hash-table :test 'equal))

并从那里填充.

我可以执行以下操作，但想对其进行抽象，以便可以以编程方式从任意深度提取值:

I can do the following, but would like to abstract it so I can programmatically pull a value from an arbitrary depth:

;;pulling from a hash that's 2 deep
(gethash "Tony Stark" (gethash "Avengers" *HEROES*))

更新-我要去做:

(defun getdeephash (hashpath h k)
  (let* ((rhashpath (reverse hashpath))
    (hashdepth (list-length hashpath))
    (hashcommand (concatenate 'string "(gethash \"" k "\"")))
   (loop for i from 1 to hashdepth
      do (setf hashcommand (concatenate 'string hashcommand "(gethash \"" (nth (- i 1) rhashpath) "\"")))
      (setf hashcommand (concatenate 'string  hashcommand " "  h (make-string (- hashdepth 0) :initial-element #\Right_Parenthesis) ")"))
      (values hashcommand)))

推荐答案

它与访问权限库:

(ql:quickload "access")

我们定义 * heroes * 哈希表(如Xach的示例):

We define the *heroes* hash table (as in Xach's example):

(defun table (&rest keys-and-values &key &allow-other-keys)
  (let ((table (make-hash-table :test 'equal)))
    (loop for (key value) on keys-and-values by #'cddr
          do (setf (gethash key table) value))
    table))
TABLE

(defparameter *heroes*
  (table "Avengers"
         (table "Retired" (table "Tony Stark" "Iron Man")
                "Active" (table "Bruce Banner" "Hulk"))))

通常，我们使用 access:access 来一致地访问各种数据结构(alist，plist，哈希表，对象等).对于嵌套访问，我们使用 access:accesses (复数):

Usually we use access:access for a consistent access to diverse data structures (alist, plist, hash table, objects,…). For a nested access we use access:accesses (plural):

(access:accesses *heroes* "Avengers" "Retired" "Tony Stark")
"Iron Man"

此外，我们可以 setf :

(setf (access:accesses *heroes* "Avengers" "Retired" "Tony Stark") "me")
"me"

这是一个经过战斗验证的库，因为它是Djula模板库的核心，而Djula模板库是下载次数最多的Quicklisp库之一.

It is a battle tested library, since it is the core of the Djula template library, one of the most downloaded Quicklisp libraries.

我的博客文章: https://lisp-journey.gitlab.io/blog/generice-consistent-access-of-data-structures-dotted-path/

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