一点儿有意义的事: SICP in Elisp

SICP常读常新, 如绘画, 层层递进, 构图, 起形, 框架, 明暗, 光线… 反复阅读, 逐次夯建, 领会书中妙处.

畅想一番, 假如SICP曾经是elisp语言写的(vice versa) 或者在1985年, SICP便有了elisp版本;编辑器圣战或成昨日烟尘, IT行业之外, Emacs或成当今的Office Suites.

做了点作业, SICP in elisp, 五章五个org文档, 其中前三章全须全尾(原文注脚, 习题, 参考答案等).

先上第一章: org笔记统计

  1. 46道习题

  2. 43个课堂案例

  3. 23个语法知识点

个性化笔记:

  1. 43处启发

  2. 两处拍案惊奇

  3. 词汇注释

以上笔记仅为打样, 上传到github库的文档, 是一字不多一字不减的书籍正文, 柱脚和图片, 习题参考答案.

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李永乐老师最新一期讲了"辅导作业的40米大砍刀"

SICP 1.3.1 黎曼积分公式

(define (integral f a b dx)
  (define (add-dx x) (+ x dx))
  (* (sum f (+ a (/ dx 2.0)) add-dx b)
     dx))

代入

#+name: case-1.3.1-integral.scm
#+BEGIN_SRC scheme :session sicp


(define (f b)
  (lambda (x) (/ 1 (sqrt
                    (- (sin x)
                       (sin b))))))

(define pi 3.141592653589793)


(define (integral2 f a b dx)
  (define (add-dx x) (+ x dx))
  (* (sum (f b)
          (+ a (/ dx 2.0))
          (lambda (x) (+ x dx))
          b)
     dx))

(* (integral2 f 0 (/ pi 6) 0.00001)
   (sqrt (/ 40
            (* 3 9.8))))
#+END_SRC

#+RESULTS: case-1.3.1-integral.scm
: 0.0-1.777598336021436i

1.777 vs 1.78

哈哈哈哈李永乐老师这个真的有毒

第一章中有趣的语法练习题

Exercise 1.5[x]

Ben Bitdiddle has invented a test to determine whether the interpreter he is faced with is using applicative-order evaluation or normal-order evaluation. He defines the following two procedures:

#+BEGIN_SRC elisp
(defun p (p)) ;; def foo(): return foo()

(defun test(x y)
  (if (= x 0)
      0
      y))
#+END_SRC

Exercise 1.6.[X]

Alyssa P. Hacker doesn’t see why if needs to be provided as a special form. ``Why can’t I just define it as an ordinary procedure in terms of cond?’’ she asks. Alyssa’s friend Eva Lu Ator claims this can indeed be done, and she defines a new version of if:

#+name: case-1.1.7-ternamy.el
#+begin_src emacs-lisp :session sicp :lexical t :results none
;; ternamy conditions
(defun new-if (predicate then-clause else-clause)
  (cond (predicate then-clause)
        (t else-clause)))
#+end_src

Delighted, Alyssa uses new-if to rewrite the square-root program: What happens when Alyssa attempts to use this to compute square roots? Explain.

#+begin_src emacs-lisp :session sicp :lexical t
(defun sqrt-iter(guess x)
  (new-if (good-enough-p guess x)
          guess
          (sqrt-iter (improve guess x)
                     x)))
(sqrt-iter 1 10)

#+end_src

Exercise 1.34[x]

Suppose we define the procedure.

#+BEGIN_SRC scheme (define (f g) (g 2)) (f square) #+END_SRC

#+RESULTS:

: (f (lambda (z) (* z (+ z 1))))
6

What happens if we (~perversely~) ask the interpreter to evaluate the combination (f f)? Explain.

SICP中的习题与正文遥相呼应, 习题既是前文的总结又是后文的引子.

比如sqrt一共给出了11种解法.

鱼骨图目录

all images added.

02. Abstraction with data

2.3.1 思路清晰的微分求导公式

#+name:  case-2.3.1-symbolic-differentiationl.el
#+begin_src emacs-lisp :session sicp :lexical t
(defun deriv(exp var) ;;v
  (cond ((numberp exp) 0) ;
        ((variable-p exp)
         (if (same-variable-p exp var) 1 0)) ;;else 0
        ((sum-p exp)
         (make-sum (deriv (addend exp) var) ;;
                   (deriv (augend exp) var)))
        ((product-p exp)
         (make-sum
           (make-product (multiplier exp)
                         (deriv (multiplicand exp) var))
           (make-product (deriv (multiplier exp) var)
                         (multiplicand exp))))
        (t
         (error "unknown expression type -- DERIV" exp))))

;; variable
(defun variable-p(x) (symbolp x))
(defun same-variable-p(v1 v2)
    (and (variable-p v1) (variable-p v2) (equal v1 v2)))
;; constructor for sum and product
(defun make-sum(a1 a2) (list '+ a1 a2))
(defun make-product(m1 m2) (list '* m1 m2))
;; predicate and selectors for sum
(defun sum-p(x)
    (and (consp x) (equal (car x) '+)))
(defun addend(s) (cadr s))
(defun augend(s) (caddr s))(cadddr '(+ 1 2 3 4))
;; predicate and seletors for product
(defun product-p(x)
     (and (consp x) (equal (car x) '*)))
(defun multiplier(p) (cadr p))
(defun multiplicand(p) (caddr p))
#+end_src

#+RESULTS: summary
: multiplicand

#+begin_src emacs-lisp :tangle yes  :results output
(print (deriv '(+ x 3) 'x))
(print (deriv '(* x y) 'x))
(print (deriv '(* (* x y) (+ x 3)) 'x))
#+end_src
#+RESULTS:

: 
  : (+ 1 0)
  : 
  : (+ (* x 0) (* 1 y))
: 
: (+ (* (* x y) (+ 1 0)) (* (+ (* x 0)

鱼骨图-质量管理七工具之一。
这本书对鱼骨图的应用耳目一新

既然读SICP, 不可避免要运行scheme,
在StackOverflow上提了半年多SICP的问题, 人民教师" Óscar López"坚贞不渝的推荐racket实现取代Gilde,

如果只拿一个充分的理由:
文档清晰全面易懂. 比如cheatsheet
https://docs.racket-lang.org/racket-cheat/index.html#(section._.Essentials)

文档

https://docs.racket-lang.org/guide/index.html

另外还有sicp专题等.

设置很简单,

首先从babel中将scheme打开

(org-babel-do-load-languages 'org-babel-load-languages '(

                                                         (scheme . t)

                                                         ))

然后安装racket

 sudo apt install racket

最后从配置中添加一行

(add-hook 'scheme-mode-hook 'geiser-mode)
(setq geiser-default-implementation 'racket)

OK了.

#+begin_src scheme :session sicp 
(* 3 3)
#+end_src

#+RESULTS:
: 9

3.Modularity, Objects and State

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4.Metalinguistic Abstration

5.Computing with Register Machines

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练习

Exercise 2.29. A binary mobile consists of two branches, a left branch and a right branch. Each branch is a rod of a certain length, from which hangs either a weight or another binary mobile. We can represent a binary mobile using compound data by constructing it from two branches (for example, using list):

中的 A binary mobile 是这样的toy

mobile-b1 mobile-b2

(家里的风铃

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