Busy week

I really wanted to get a lot more done this week, but final result is that still not done with chapter 2.2

Getting started during a holiday at least helped get some speed... Now I need another to maintain it.

Here's 2.41 just for the hell of it

(define (triples n)
    (flatmap (lambda (i)
               (map (lambda (j) (cons i j))
                    (unique-pairs (- i 1))))
             (enumerate-interval 1 n)))
(define (s-triples target max)
    (filter (lambda (x) (= target (accumulate + 0 x))) (triples max)))

Also some definitions that might be needed:

(define (unique-pairs n)
    (flatmap (lambda (i)
               (map (lambda (j) (list i j))
                    (enumerate-interval 1 (- i 1))))
               (enumerate-interval 1 n)))

(define (enumerate-interval start n)
    (define (enumerate x)
      (if (< n x)
          null
          (cons x (enumerate (+ 1 x)))))
    (enumerate start))

(define (filter predicate sequence)
  (cond ((null? sequence) null)
        ((predicate (car sequence))
         (cons (car sequence)
               (filter predicate (cdr sequence))))
        (else (filter predicate (cdr sequence)))))