sicp

In SICP exercise 2.26, this Scheme code is given: (define x (list 1 2 3)) (define y (list 4 5 6)) Then this cons call is given: (cons x y) I expected a pair of lists would result, ((1 2 3) (4 5 6)) but the interpreter gives, ((1 2 3) 4 5 6) ...a list with 4 elements, the first being a list. Why is y treated differently? I've tried looking up other SICP answers for an explanation, but couldn't find something satisfactory. So could any Scheme/Lisp experts please shed some light on this aspect of cons? Thanks in advance for any insight. '((1 2 3) 4 5 6) is actually a pair of lists. Here's another

I'm working through the streams section of the scip and am stuck on how to define a stream. The following is my code: (define (memo-func function) (let ((already-run? false) (result false)) (lambda () (if (not already-run?) (begin (set! result (function)) (set! already-run? true) result) result)))) (define (delay exp) (memo-func (lambda () exp))) (define (force function) (function)) (define the-empty-stream '()) (define (stream-null? stream) (null? stream)) (define (stream-car stream) (car stream)) (define (stream-cdr stream) (force (cdr stream))) (define (cons-stream a b) (cons a (memo-func

I'm having trouble reading output from dr racket. By default it displays lists using mcons. For example, sicp exercise 2.32 produces: > (subsets (list 1 2 3)) (mcons (mcons '() (mcons (mcons 3 '()) (mcons (mcons 2 '()) (mcons (mcons 2 (mcons 3 '())) (mcons (mcons 1 '()) (mcons (mcons 1 (mcons 3 '())) (mcons (mcons 1 (mcons 2 '())) (mcons (mcons 1 (mcons 2 (mcons 3 '()))) '())))))))) '()) I'm having trouble reading this. Is there a way to make the output look like: (() (3) (2) (2 3) (1) (1 3) (1 2) (1 2 3)) Thanks! Do you know what language are you using in your #lang line? The rest of the

I've been working through in Structure and Interpretation of Computer Programs and completing the exercises in Haskell. The first two chapters were fine (code at github ) but Chapter 3 is making me think harder. It starts by talking about managing state, with the example of a bank account. They define a function make-withdraw by (define (make-withdraw balance) (lambda (amount) (if (>= balance amount) (begin (set! balance (- balance amount)) balance) "Insufficient funds"))) so that you can execute the following code: (define w1 (make-withdraw 100)) (define w2 (make-withdraw 100)) (w1 50) 50 (w2

I have found the code from this lesson online (http://groups.csail.mit.edu/mac/ftpdir/6.001-fall91/ps4/matcher-from-lecture.scm), and I am having a heck of a time trying to debug it. The code looks pretty comparable to what Sussman has written: ;;; Scheme code from the Pattern Matcher lecture ;; Pattern Matching and Simplification (define (match pattern expression dictionary) (cond ((eq? dictionary 'failed) 'failed) ((atom? pattern) (if (atom? expression) (if (eq? pattern expression) dictionary 'failed) 'failed)) ((arbitrary-constant? pattern) (if (constant? expression) (extend-dictionary