; Collected Scheme code of Section 11.5 from
; Kenneth C. Louden, Programming Languages
; Principles and Practice 2nd Edition
; Copyright (C) Brooks-Cole/ITP, 2003

; page 508

(define (p x y) (if x 1 (y)))

(p #T (lambda ( ) (/ 1 0)))

; page 509

(define ( p x y) (if x 1 (force y)))

(p #T (delay (/ 1 0)))

(define (delayed-square x) (* (force x) (force x)))

(define (take n L)
  (if (= n 0 ) '()
      (cons ( car (force L)) (take (- n 1)
                              (cdr (force L))))))

(define (intlist m n)
  (if (> m n) '() (cons m (intlist (+ 1 m) n))))

; page 510

(take 1 (delay (intlist 2 100)))

(define (intlist m n)
  (if (> m n) '() 
      (cons m (delay (intlist (+ 1 m) n)))))

(take 1 (delay (intlist 2 100)))

; page 511

(define (flatten L)
 (cond ((null? L) '())
       ((list? L) (append (flatten (car L)) 
                          (flatten (cdr L))))
       (else (cons L '()) )))

(define (samefringe? L M) (equal? (flatten L)
                                  (flatten M)))