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  1. ; ordered cartesian coordinates
  2.  
  3. (define-syntax fold-of
  4.   (syntax-rules (range in is)
  5.     ((_ "z" f b e) (set! b (f b e)))
  6.     ((_ "z" f b e (v range fst pst stp) c ...)
  7.       (let* ((x fst) (p pst) (s stp)
  8.              (le? (if (positive? s) <= >=)))
  9.         (do ((v x (+ v s))) ((le? p v) b)
  10.           (fold-of "z" f b e c ...))))
  11.     ((_ "z" f b e (v range fst pst) c ...)
  12.       (let* ((x fst) (p pst) (s (if (< x p) 1 -1)))
  13.         (fold-of "z" f b e (v range x p s) c ...)))
  14.     ((_ "z" f b e (v range pst) c ...)
  15.       (fold-of "z" f b e (v range 0 pst) c ...))
  16.     ((_ "z" f b e (x in xs) c ...)
  17.       (do ((t xs (cdr t))) ((null? t) b)
  18.         (let ((x (car t)))
  19.           (fold-of "z" f b e c ...))))
  20.     ((_ "z" f b e (x is y) c ...)
  21.       (let ((x y)) (fold-of "z" f b e c ...)))
  22.     ((_ "z" f b e p? c ...)
  23.       (if p? (fold-of "z" f b e c ...)))
  24.     ((_ f i e c ...)
  25.       (let ((b i)) (fold-of "z" f b e c ...)))))
  26.  
  27. (define-syntax list-of (syntax-rules ()
  28.   ((_ arg ...) (reverse (fold-of
  29.     (lambda (d a) (cons a d)) '() arg ...)))))
  30.  
  31. (define sort #f)
  32. (define merge #f)
  33. (let ()
  34.   (define dosort
  35.     (lambda (pred? ls n)
  36.       (if (= n 1)
  37.           (list (car ls))
  38.           (let ((i (quotient n 2)))
  39.             (domerge pred?
  40.                      (dosort pred? ls i)
  41.                      (dosort pred? (list-tail ls i) (- n i)))))))
  42.   (define domerge
  43.     (lambda (pred? l1 l2)
  44.       (cond
  45.         ((null? l1) l2)
  46.         ((null? l2) l1)
  47.         ((pred? (car l2) (car l1))
  48.          (cons (car l2) (domerge pred? l1 (cdr l2))))
  49.         (else (cons (car l1) (domerge pred? (cdr l1) l2))))))
  50.   (set! sort
  51.     (lambda (pred? l)
  52.       (if (null? l) l (dosort pred? l (length l)))))
  53.   (set! merge
  54.     (lambda (pred? l1 l2)
  55.       (domerge pred? l1 l2))))
  56.  
  57. (define (lt? x y)
  58.   (or (< (car x) (car y))
  59.       (and (= (car x) (car y))
  60.            (< (cadr x) (cadr y)))))
  61.  
  62. (define (pairs n)
  63.   (map cdr (sort lt?
  64.     (list-of (list (* a b) a b)
  65.       (a range 1 (+ n 1))
  66.       (b range 1 (+ n 1))))))
  67.  
  68. (display (pairs 0)) (newline)
  69. (display (pairs 1)) (newline)
  70. (display (pairs 2)) (newline)
  71. (display (pairs 3)) (newline)
Success #stdin #stdout 0.01s 7272KB
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Standard input is empty
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()
((1 1))
((1 1) (1 2) (2 1) (2 2))
((1 1) (1 2) (2 1) (1 3) (3 1) (2 2) (2 3) (3 2) (3 3))
https://ideone.com/lM3rIs
language:
()
created:
9 years ago
visibility:
public

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