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let*和set之间的区别?在公共Lisp中

common-lisp lisp macros

Paul Nathan · 技术社区 · 14 年前

我正在做一个基因编程爱好项目。

我有一个函数/宏设置,当以setq/setf形式计算时,它将生成一个类似这样的列表。

(setq trees (make-trees 2)) 
==> (+ x (abs x))

然后它将被绑定到一个lambda函数 #<FUNCTION :LAMBDA (X) ... > 通过战略性地使用函数/宏

但是,我想用它比手动分配变量更有效一些,所以我写了如下内容:

(setq sample 
      (let* ((trees (make-trees 2))
         (tree-bindings (bind-trees trees))
         (evaluated-trees (eval-fitness tree-bindings))))
      (list (trees tree-bindings evaluated-trees)))

EVAL: trees has no value 当我把这个放在一个let表格里。我的怀疑是,与SETF相比,宏扩展并没有在LET中完全执行,但这对我来说毫无意义。

---编辑:拉我的代码,把整个文件在一个粘贴箱---

假设我决定setq不会为我做这件事,我写了一个简单的函数:

(让((树枝(做树2))) (let((求值树(求值适应度树绑定)))

我有理由肯定我已经完全冲洗了我的宏。 http://pastebin.org/673619

1 回复 | 直到 14 年前

Svante 14 年前

(Setq make-trees 2) 设置变量的值 make-trees 到2,然后返回2。

造树 创建一个可以解释为程序的随机树?把它定义为一个函数 defun . 我在想这样的事情:

(defun make-tree (node-number)
  (if (= node-number 1)
      (make-leaf)
      (cons (get-random-operator)
            (mapcar #'make-tree
                    (random-partition (- node-number 1))))))

Let 和 setq 做完全不同的事情。 Setq 为现有变量赋值,而 let

我认为您应该提供更多的代码;目前,您的问题没有什么意义。

更新:

我将修复代码段的缩进以使事情更清楚:

(setq sample 
      (let* ((trees (make-trees 2))
             (tree-bindings (bind-trees trees))
             (evaluated-trees (eval-fitness tree-bindings))))
      (list (trees tree-bindings evaluated-trees)))

let* 建立词汇绑定。这些仅在其主体范围内:

(setq sample 
      (let* ((trees (make-trees 2))
             (tree-bindings (bind-trees trees))
             (evaluated-trees (eval-fitness tree-bindings)))
        ;; here trees, tree-bindings, and evaluated-trees are bound
        ) ; end of let* body
      ;; here trees, tree-bindings, and evaluated trees are not in scope anymore
      (list (trees tree-bindings evaluated-trees)))

返回一个元素的列表,这将是计算的结果函数 trees tree-bindings evaluated-trees 论据。

(setq sample 
      (let* ((trees (make-trees 2))
             (tree-bindings (bind-trees trees))
             (evaluated-trees (eval-fitness tree-bindings)))
        (list trees tree-bindings evaluated-trees)))

另一个更新:

下面是一些可能对您有所帮助的代码:

(defun make-tree-lambda (depth)
  (list 'lambda '(x)
        (new-tree depth)))

(defun make-tree-function (lambda-tree)
  (eval lambda-tree))

(defun eval-fitness (lambda-form-list input-output-list)
  "Determines how well the lambda forms approach the wanted function
by comparing their output with the wanted output in the supplied test
cases.  Returns a list of mean quadratic error sums."
  (mapcar (lambda (lambda-form)
            (let* ((actual-results (mapcar (make-tree-function lambda-form)
                                           (mapcar #'first input-output-list)))
                   (differences (mapcar #'-
                                        actual-results
                                        (mapcar #'second input-output-list)))
                   (squared-differences (mapcar #'square
                                                differences)))
              (/ (reduce #'+ squared-differences)
                 (length squared-differences))))
          lambda-form-list))

(defun tree-fitness (tree-list input-output-list)
  "Creates a list of lists, each inner list is (tree fitness). Input
is a list of trees, and a list of test cases."
  (mapcar (lambda (tree fitness)
            (list tree fitness))
          tree-list
          (eval-fitness (mapcar #'make-tree-lambda tree-list)
                        input-output-list)))