Scheme

• 特点
  • 词法定界(Lexical Scoping)
  • 动态类型(Dynamic Typing)
  • 良好的可扩展性
  • 尾递归(Tail Recursive)
  • 函数作为值返回
  • 计算连续
  • 传值调用(passing-by-value)
  • 算术运算相对独立
• 标准
  • R5RS (Revised5 Report on the Algorithmic Language Scheme)
  • Guile (GNU’s extension language)
• guile脚本中(.scm)
  • #! /usr/local/bin/guile -s
  • !#
• 语法
  • 注释
    • ;
      • 注释到行尾
    • #! … !#
      • 标准中没有，实现中有的多行注释
  • 类型
    • 1
    • ‘symbol
    • “str”
    • true, false
    • struct
    • empty
      • 表示一个空表
  • 块(form)
    • (define x 123)
    • (set! x “abc”)
    • (+ 1 2)
    • (* (+ 2 (* 3 4)) (+ 5 6 7))
    • (display “hello world”)
    • (not #f)
      • #t
    • (not #t)
      • #f
      • not 后不是逻辑型，都返回#f
  • 非精确数
    • (- #i1.0 #i0.9)
  • 函数
    • or
    • and
    • not
    • (sqrt A)
    • (expt A B)
      • A
    • (remainder A B)
      • A%B
    • (log A)
      • A的自然对数
    • (sin A)
    • (cond
      • [(< n 10) 5.0]
      • [else .06])
    • (if (< x 0)
      • (- x)
      • x)
    • (symbol=? ‘Hello x)
      • 符号，比较。符号还有字符串和图像
    • (string=? “the dog” x)
      • 字符串，系统看作符号
    • (make-posn 3 4)
      • 创建posn结构体
      • (poson-x (make-posn 7 0))
        • 7
    • (define-struct posn (x y))
      • 定义结构体
    • (number?)
    • (boolean?)
    • (struct?)
    • (zero?)
    • (posn?)
      • 可以是自定义结构体名
    • (null?)
      • 检查是否空list
    • (eq? i list)
      • 元素i是否在list中， 否返回false, 是返回所在的子表
      • 可以比较符号
    • (memq)
      • eq?的内部调用
    • (error ”checked-number “number expected”)
      • 马上出错
    • (cons ‘Mercury empty)
      • push
      • (cons? alon)
        • 是否有元素
      • (define x (cons 1 2))
        • 序对, 可嵌套
        • (car x)
          • 1
        • (cdr x)
          • 2
    • (define (dispatch m)
      • 传0返回x, 传1返回y
      • (cond ((= m 0) x)
        • ((= m 1) y)
        • (else (error "" m))))
    • (first)
    • (rest)
    • (list (list ‘bob 0 ‘a) (list ‘car1 1 ‘a))
    • (local)
      • 局部定义使用
    • (lambda)
      • 匿名函数
    • (append)
    • (set! x 5)
• 例子
  • 复合数据
    • (define-struct student (last first teacher))
    • (define (subst-teacher a-student a-teacher)
      • (cond
        • [(symbol=? (student-teacher a-student) ‘Fritz)
          • 如果教师的名字是’Fritz
          • (make-student (student-last a-student)
            • 创建student结构体，设置新教师名
            • (student-first a-student)
            • a-teacher)]
        • [else a-student]))
  • 递归列表
    • (define (contains-doll? a-list-of-symbols)
      • (cond
        • [(empty? a-list-of-symbols) false]
        • [else (cond
          • [(symbol=? (first a-list-of-symbols) ‘doll) true]
          • [else (contains-doll? (rest a-list-of-symbols))])]))
  • 排序
    • (define (sort alon)
      • (cond
        • [(empty? alon) empty]
        • [(cons? alon) (insert (first alon) (sort (rest alon)))]))
    • (define (insert n alon)
      • (cond
        • [(empty? alon) (cons n empty)]
        • [else (cond
          • [(>= n (first alon)) (cons n alon)]
          • [(< n (first alon)) (cons (first alon) (insert n (rest alon)))])]))
  • or函数
    • (define (blue-eyed-ancestor? a-ftree)
      • (cond
        • [(empty? a-ftree) false]
        • [else (or (symbol=? (child-eyes a-ftree) ‘blue)
          • (or (blue-eyed-ancestor? (child-father a-ftree))
            • (blue-eyed-ancestor? (child-mother a-ftree))))]))
  • 列表替换
    • (define (replace-eol-with alon1 alon2)
      • (cond
        • ((empty? alon1) alon2)
        • (else (cons (first alon1) (replace-eol-with (rest alon1) alon2)))))
  • 列表相等
    • (define (list=? a-list another-list)
      • (cond
        • [(empty? a-list) (empty? another-list)]
        • [(cons? a-list)
          • (and (cons? another-list)
            • (and (= (first a-list) (first another-list))
              • (list=? (rest a-list) (rest another-list))))]))
  • 匿名函数
    • (define (find aloir t)
      • (filter1 (local ((define (eq-ir? ir p)
        • (symbol=? (ir-name ir) p)))
          • eq-ir?)
        • aloir t))
    • (lambda (ir p) (symbol=? (ir-name ir) p))
  • 快速排序
    • (define (quick-sort alon)
      • (cond
        • [(empty? alon) empty]
        • [else (append
          • (quick-sort (smaller-items alon (first alon)))
          • (list (first alon))
          • (quick-sort (larger-items alon (first alon))))]))
    • (define (larger-items alon threshold)
      • (cond
        • [(empty? alon) empty]
        • [else (if (> (first alon) threshold)
          • (cons (first alon) (larger-items (rest alon) threshold))
          • (larger-items (rest alon) threshold))]))
    • (define (smaller-items alon threshold)
      • (cond
        • [(empty? alon) empty]
        • [else (if (< (first alon) threshold)
          • (cons (first alon) (smaller-items (rest alon) threshold))
          • (smaller-items (rest alon) threshold))]))