---

title: Debit Reading Session - SICP solutions pt.1

date: 2021-06-08

layout: post

lang: en

ref: debit-reading-session-sicp-solutions-pt-1

---

```scheme
;; 1.41
(define (double f)
  (lambda (x)
    (f (f x))))


:;; 1.42
(define (compose f g)
  (lambda (x)
    (f (g x))))


;;; 1.43
(define (repeated f n)
  (if (= 1 n)
    identity
    (comp (repeated f (dec n)))))


;;; 2.27
(define (map-tree node-fn leaf-fn tree)
  (cond
   ((null? tree) tree)
   ((not (pair? tree)) (leaf-fn tree))
   (else
    (node-fn
     (cons (map-tree node-fn leaf-fn (car tree))
           (map-tree node-fn leaf-fn (cdr tree)))))))

(define (map-nodes f tree)
  (map-tree f identity tree))

(define (deep-reverse x)
  (map-nodes reverse x))


;;; 2.28
(define (flatten tree)
  (define (rec acc t)
    (cond
     ((null? t) acc)
     ((not (pair? t)) (cons t acc))
     (else
      (rec (rec (cdr t) acc)
           (car t)))))
  (rec nil tree))


;;; 2.30
(define (square-tree tree)
  (map-leaves square tree))


;;; 2.31
(define square-tree map-leaves) ; ha!


;;; 2.32
TODO
```

FYI: I just typed those in, I didn't yet test them yet.