uploaded homework1~8(2017)

Most of these code is shortest in scoreboard

Author: Halbmond

2015final/combine-f1-f2-n.scm

@@ -0,0 +1,27 @@
+#lang racket
+
+(define (square x) (* x x))
+(define (inc x) (+ x 1))
+(define (db x) (* x 2))
+
+(define (combine f1 f2 n)
+;MY CODE BEGIN
+(define (combine2 g1 g2) (lambda (x) (g1 (g2 x))))
+(foldl combine2 values (build-list n (lambda (i) (combine2 f1 f2)))))
+;MY CODE END
+((combine square inc 1) 2)
+((combine square inc 2) 3)
+((combine db inc 3) 2)
+((combine inc inc 4) 3)
+
+(display "********") (newline)
+
+(define (myloop)
+ (let ((n (read))
+ (x (read)))
+ (if (eq? n eof)
+ (void)
+ (begin (display ((combine inc square n) x)) 
+ (newline) (myloop)))))
+
+(myloop)

2015final/divide-number.scm

@@ -0,0 +1,21 @@
+;f[i][j] = f[i][j-1] + f[i-j][min(i-j,j)]
+#lang racket
+(define N 201)
+(define f (build-vector 201 (lambda (x) (make-vector 201 0))))
+(define (Fr x y) (vector-ref (vector-ref f x) y))
+(define (Fs x y k) (vector-set! (vector-ref f x) y k))
+(Fs 0 0 1)
+(for-each (lambda (i)
+(for-each (lambda (j)
+(Fs i j (+ (Fr i (- j 1)) (Fr (- i j) (min (- i j) j))))
+) (range 1 (+ i 1)))
+) (range 1 201))
+(let loop ()
+(let ([n (read)])
+(unless (eq? n eof)
+(displayln (Fr n n))
+(loop)
+)
+)
+)
+

2015final/ex-3.55-partial-sums.scm

@@ -0,0 +1,41 @@
+#lang racket
+;book ex 3.55
+(require r5rs)
+(define env (scheme-report-environment 5))
+(eval '(define (stream-car stream) (car stream)) env)
+(eval '(define (stream-cdr stream) (force (cdr stream))) env)
+(eval '(define-syntax cons-stream
+(syntax-rules ()
+[(cons-stream x y) (cons x (delay y))])) env)
+
+(eval '(define the-empty-stream '()) env)
+(eval '(define (stream-null? stream) (null? stream)) env)
+ 
+(eval '(define (stream-ref s n) ;取 stream里面第 n 项,n从0开始算
+(if (stream-null? s) the-empty-stream
+(if (= n 0)
+(stream-car s)
+(stream-ref (stream-cdr s) (- n 1)))))
+env)
+
+
+(eval '
+ (define (partial-sums op s) ;以s为参数,返回的流是 s0,(op s0 s1),(op s0 s1 s2), ....
+;MY CODE BEGIN (define (partial-sums op s) ;以s为参数,返回的流是 s0,(op s0 s1),(op s0 s1 s2), ....
+(define (partial-sums-and-add op s0 s)
+(cons-stream (op s0 (stream-car s)) (partial-sums-and-add op (op s0 (stream-car s)) (stream-cdr s))))
+(cons-stream (stream-car s) (partial-sums-and-add op (stream-car s) (stream-cdr s))))
+;MY CODE END
+env)
+
+(define (myloop)
+(define (eval-codes codes last-val)
+(if (null? codes)
+last-val
+(eval-codes (cdr codes) (eval (car codes) env))))
+
+(let ((codes (read)))
+(if (eq? codes eof)
+(void)
+(begin (displayln (eval-codes codes (void))) (myloop)))))
+(myloop)