电脑程序的结构和编译.pptVIP

Structure Interpretation of Computer Programs 电脑程序的结构和编译 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 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 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 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 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 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 Prefix Notation / 前缀表示法 The function (函数) always comes before its arguments (+ 3 4) (- 5 3) (* 5 4) 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)x3 Combining Ideas (define x 12) 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? Defining Procedures (cont.) (define (square arg) (* arg arg)) Weakly Typed Unlike C++ and Java, scheme does not worry about types! Dont 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) 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))) Recursion (next lecture) A recursive procedure calls itself Factorial(n) =