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  1. (define (fold c z xs)
  2.    (cond ((null? xs) z)
  3.          (else (fold c (c (car xs) z) (cdr xs)))))
  4.  
  5. (define (comp f g) (lambda (x)
  6.   (f (g x))))
  7.  
  8. (define (cons1 x) (lambda (y)
  9.   (cons x y)))
  10.  
  11. (define (filter p xs)
  12.   ((fold (lambda (x k)
  13.            (if (p x) (comp k (cons1 x)) k))
  14.          (lambda (x) x)
  15.          xs)
  16.    '()))
  17.  
  18. (display (filter (lambda(x)(= (remainder x 2) 0)) (list 1 2 3 4 5)))
  19. #|
  20. (define (foldd c z xs)
  21.    (cond ((null? xs) (z '()))
  22.          (else (foldd c (c (car xs) z) (cdr xs)))))
  23.  
  24. (define (comp f g) (lambda (x)     ; ((comp f g) x)
  25.   (f (g x))))
  26.  
  27. (define (cons1 x) (lambda (y)      ; ((cons1 x) y)
  28.   (cons x y)))
  29.  
  30. (define (filter p xs)
  31.   (foldd (lambda (x k)
  32.            (if (p x) (comp k (cons1 x)) k))
  33.          (lambda (x) x)
  34.          xs))
  35.  
  36. (display (filter (lambda(x)(= (remainder x 2) 0)) (list 1 2 3 4 5)))
  37. |#
Success #stdin #stdout 0.03s 8616KB
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https://ideone.com/sWodW7
language:
Scheme (guile 2.2.4)
created:
8 years ago
visibility:
secret

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