1. Structure & Interpretation of Computer Programs Xiao Ben Charrow

2. 电脑程序的结构和编译 萧潇 陈斌

3. Who We Are Xiao Xiao MIT, Junior, Majoring in Computer Science x_x@mit.edu Ben Charrow MIT, Senior, Majoring in Computer Science bcharrow@mit.edu

4. What We Want to Cover The "Scheme" programming language Data Abstraction / 数据抽象 Iterative and recursive processes / 重复和递归进程 Data structures / 数据结构 Basic algorithms / 算法

5. Our Bible / 我们的圣经 电脑程序的 结构和编译 SICP (sick-pea) Wizard Book / 巫师书

6. Scheme Language features Simple (syntax / 语法 & specification / 规格 ) Prefix notation / 前缀表示法 Interpreted / 解释器 Tail-recursive / 尾递归 Weakly typed / 弱类型 Functional

7. Simplicity The Scheme specification is 50 pages long The Java specification is 684 pages long Scheme is designed to be as simple and small as possible

8. Interpreters / 解释器 Characteristics Each line of code is only examined at runtime / 运行时间 Works on all computer architectures / 计算机体系结构 Easy to fix problems Slower than compiled / 编译器 code

9. Scheme Keywords Keywords: Words that have a 'special meaning' to the scheme interpreter They are what allow you to make programs

10. Prefix Notation / 前缀表示法 The function ( 函数 ) always comes before its arguments (+ 3 4) (- 5 3) (* 5 4) 7 2 20

11. Keyword Example: define (define x y) Makes the value of x the value of y Does not work if y does not have a value (define x 3) x 3

12. Combining Ideas (define x 12) (define x 5) (define y x) (* x y) 25 15 (+ x 3)

13. Defining Procedures Want to define a function that squares its argument Call the function 'square' Call the argument 'arg' How do we write it in scheme?

14. Defining Procedures (cont.) (define (square arg) (* arg arg)) (square 4) 16

15. Weakly Typed Unlike C++ and Java, scheme does not worry about types! Don't need to declare variables as 'int' or 'char' Makes generalizing code easier Be careful what you pass! (define (add arg1 arg2) (+ arg1 arg2)) (add 'a 'b)

16. Another Keyword: cond cond Similar to the 'if' statement in C++ or Java If predicate is #t / true, then it evaluates the statement If predicate is #f / false, then it moves on (define (sign? arg) (cond ((> 0 arg) ’negative) ((< 0 arg) ’positive) (else 'zero)))

17. Recursion (next lecture) A 'recursive procedure' calls itself Factorial(n) = n! If n > 0, Factorial(n) = n*Factorial(n-1) otherwise factorial(n) = 1 Factorial is a recursive procedure