[ create a new paste ] login | about

Project: programmingpraxis
Link: http://programmingpraxis.codepad.org/gUUqP8fm    [ raw code | fork ]

programmingpraxis - Scheme, pasted on Jun 29:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
;;; standard prelude


; list utilities

(define (take n xs)
  (let loop ((n n) (xs xs) (ys '()))
    (if (or (zero? n) (null? xs))
        (reverse ys)
        (loop (- n 1) (cdr xs)
              (cons (car xs) ys)))))

(define (drop n xs)
  (let loop ((n n) (xs xs))
    (if (or (zero? n) (null? xs)) xs
      (loop (- n 1) (cdr xs)))))

(define (take-while pred? xs)
  (let loop ((xs xs) (ys '()))
    (if (or (null? xs) (not (pred? (car xs))))
        (reverse ys)
        (loop (cdr xs) (cons (car xs) ys)))))

(define (drop-while pred? xs)
  (let loop ((xs xs))
    (if (or (null? xs) (not (pred? (car xs)))) xs
      (loop (cdr xs)))))

(define (cons* first . rest)
  (let loop ((curr first) (rest rest))
    (if (null? rest) curr
        (cons curr (loop (car rest) (cdr rest))))))

(define (fold-left op base xs)
  (if (null? xs)
      base
      (fold-left op (op base (car xs)) (cdr xs))))

(define (fold-right op base xs)
  (if (null? xs)
      base
      (op (car xs) (fold-right op base (cdr xs)))))

(define (range . args)
  (case (length args)
    ((1) (range 0 (car args) (if (negative? (car args)) -1 1)))
    ((2) (range (car args) (cadr args) (if (< (car args) (cadr args)) 1 -1)))
    ((3) (let ((le? (if (negative? (caddr args)) >= <=)))
           (let loop ((x(car args)) (xs '()))
             (if (le? (cadr args) x)
                 (reverse xs)
                 (loop (+ x (caddr args)) (cons x xs))))))
    (else (error 'range "unrecognized arguments"))))

(define (iterate n f . bs)
  (let loop ((n n) (b (car bs)) (bs (cdr bs)) (xs '()))
    (if (zero? n) (reverse xs)
      (let ((new-bs (append bs (list (apply f b bs)))))
        (loop (- n 1) (car new-bs) (cdr new-bs) (cons b xs))))))

(define (filter pred? xs)
  (let loop ((xs xs) (ys '()))
    (cond ((null? xs) (reverse ys))
          ((pred? (car xs))
            (loop (cdr xs) (cons (car xs) ys)))
          (else (loop (cdr xs) ys)))))

(define (remove x xs)
  (let loop ((xs xs) (zs '()))
    (cond ((null? xs) (reverse zs))
          ((equal? (car xs) x) (loop (cdr xs) zs))
          (else (loop (cdr xs) (cons (car xs) zs))))))

(define (flatten xs)
  (cond ((null? xs) xs)
        ((pair? xs)
          (append (flatten (car xs))
                  (flatten (cdr xs))))
        (else (list xs))))

(define (all? pred? xs)
  (cond ((null? xs) #t)
        ((pred? (car xs))
          (all? pred? (cdr xs)))
        (else #f)))

(define (any? pred? xs)
  (cond ((null? xs) #f)
        ((pred? (car xs)) #t)
        (else (any? pred? (cdr xs)))))

(define (zip . xss) (apply map list xss))

(define (cross . xss)
  (define (f xs yss)
    (define (g x zss)
      (define (h ys uss)
        (cons (cons x ys) uss))
      (fold-right h zss yss))
    (fold-right g '() xs))
  (fold-right f (list '()) xss))

(define (make-list n x)
  (let loop ((n n) (xs '()))
    (if (zero? n) xs
      (loop (- n 1) (cons x xs)))))

(define (sum xs) (apply + xs))


; list comprehensions

(define-syntax fold-of
  (syntax-rules (range in is)
    ((_ "z" f b e) (set! b (f b e)))
    ((_ "z" f b e (v range fst pst stp) c ...)
      (let* ((x fst) (p pst) (s stp)
             (le? (if (positive? s) <= >=)))
        (do ((v x (+ v s))) ((le? p v) b)
          (fold-of "z" f b e c ...))))
    ((_ "z" f b e (v range fst pst) c ...)
      (let* ((x fst) (p pst) (s (if (< x p) 1 -1)))
        (fold-of "z" f b e (v range x p s) c ...)))
    ((_ "z" f b e (v range pst) c ...)
      (fold-of "z" f b e (v range 0 pst) c ...))
    ((_ "z" f b e (x in xs) c ...)
      (do ((t xs (cdr t))) ((null? t) b)
        (let ((x (car t)))
          (fold-of "z" f b e c ...))))
    ((_ "z" f b e (x is y) c ...)
      (let ((x y)) (fold-of "z" f b e c ...)))
    ((_ "z" f b e p? c ...)
      (if p? (fold-of "z" f b e c ...)))
    ((_ f i e c ...)
      (let ((b i)) (fold-of "z" f b e c ...)))))

(define-syntax list-of (syntax-rules ()
  ((_ arg ...) (reverse (fold-of
    (lambda (d a) (cons a d)) '() arg ...)))))

(define-syntax sum-of (syntax-rules ()
  ((_ arg ...) (fold-of + 0 arg ...))))


; pattern matching

(define-syntax list-match
  (syntax-rules ()
    ((_ expr (pattern fender ... template) ...)
      (let ((obj expr))
        (cond ((list-match-aux obj pattern fender ...
                (list template)) => car) ...
              (else (error 'list-match "pattern failure")))))))

(define-syntax list-match-aux
  (lambda (stx)
    (define (underscore? x)
      (and (identifier? x) (free-identifier=? x (syntax _))))
    (syntax-case stx (quote quasiquote)
      ((_ obj pattern template)
        (syntax (list-match-aux obj pattern #t template)))
      ((_ obj () fender template)
        (syntax (and (null? obj) fender template)))
      ((_ obj underscore fender template)
        (underscore? (syntax underscore))
        (syntax (and fender template)))
      ((_ obj var fender template)
        (identifier? (syntax var))
        (syntax (let ((var obj)) (and fender template))))
      ((_ obj (quote datum) fender template)
        (syntax (and (equal? obj (quote datum)) fender template)))
      ((_ obj (quasiquote datum) fender template)
        (syntax (and (equal? obj (quasiquote datum)) fender template)))
      ((_ obj (kar . kdr) fender template)
        (syntax (and (pair? obj)
                (let ((kar-obj (car obj)) (kdr-obj (cdr obj)))
                  (list-match-aux kar-obj kar
                        (list-match-aux kdr-obj kdr fender template))))))
      ((_ obj const fender template)
        (syntax (and (equal? obj const) fender template))))))


; matrices

(define (make-matrix rows columns . value)
  (do ((m (make-vector rows)) (i 0 (+ i 1)))
      ((= i rows) m)
    (if (null? value)
        (vector-set! m i (make-vector columns))
        (vector-set! m i (make-vector columns (car value))))))

(define (matrix-rows x) (vector-length x))

(define (matrix-cols x) (vector-length (vector-ref x 0)))

(define (matrix-ref m i j) (vector-ref (vector-ref m i) j))

(define (matrix-set! m i j x) (vector-set! (vector-ref m i) j x))

(define-syntax for
  (syntax-rules ()
    ((for (var first past step) body ...)
      (let ((ge? (if (< first past) >= <=)))
        (do ((var first (+ var step)))
            ((ge? var past))
          body ...)))
    ((for (var first past) body ...)
      (let* ((f first) (p past) (s (if (< first past) 1 -1)))
        (for (var f p s) body ...)))
    ((for (var past) body ...)
      (let* ((p past)) (for (var 0 p) body ...)))))


; hash tables

(define (make-hash hash eql? oops size)
  (let ((table (make-vector size '())))
    (lambda (message . args)
      (if (eq? message 'enlist)
          (let loop ((k 0) (result '()))
            (if (= size k)
                result
                (loop (+ k 1) (append (vector-ref table k) result))))
          (let* ((key (car args))
                 (index (modulo (hash key) size))
                 (bucket (vector-ref table index)))
            (case message
              ((lookup fetch get ref recall)
                (let loop ((bucket bucket))
                  (cond ((null? bucket) oops)
                        ((eql? (caar bucket) key) (cdar bucket))
                        (else (loop (cdr bucket))))))
              ((insert insert! ins ins! set set! store store! install install!)
                (vector-set! table index
                  (let loop ((bucket bucket))
                    (cond ((null? bucket)
                            (list (cons key (cadr args))))
                          ((eql? (caar bucket) key)
                            (cons (cons key (cadr args)) (cdr bucket)))
                          (else (cons (car bucket) (loop (cdr bucket))))))))
              ((delete delete! del del! remove remove!)
                (vector-set! table index
                  (let loop ((bucket bucket))
                    (cond ((null? bucket) '())
                          ((eql? (caar bucket) key)
                            (cdr bucket))
                          (else (cons (car bucket) (loop (cdr bucket))))))))
              ((update update!)
                (vector-set! table index
                  (let loop ((bucket bucket))
                    (cond ((null? bucket)
                            (list (cons key (caddr args))))
                          ((eql? (caar bucket) key)
                            (cons (cons key ((cadr args) key (cdar bucket))) (cdr bucket)))
                          (else (cons (car bucket) (loop (cdr bucket))))))))
              (else (error 'hash-table "unrecognized message")) ))))))

(define (string-hash str)
  (let loop ((cs (string->list str)) (s 0))
    (if (null? cs) s
      (loop (cdr cs) (+ (* s 31)
        (char->integer (car cs)))))))

(define (list->hash hash eql? oops size xs)
  (let ((table (make-hash hash eql? oops size)))
    (do ((xs xs (cdr xs))) ((null? xs) table)
      (table 'insert (caar xs) (cdar xs)))))


; input/output

(define (for-each-input reader proc . pof)
  (let* ((f? (and (pair? pof) (string? (car pof))))
         (p (cond (f? (open-input-file (car pof)))
                  ((pair? pof) (car pof))
                  (else (current-input-port)))))
    (do ((item (reader p) (reader p)))
        ((eof-object? item)
          (if f? (close-input-port p)))
      (proc item))))

(define (map-input reader proc . pof)
  (let* ((f? (and (pair? pof) (string? (car pof))))
         (p (cond (f? (open-input-file (car pof)))
                  ((pair? pof) (car pof))
                  (else (current-input-port)))))
    (let loop ((item (reader p)) (result '()))
      (if (eof-object? item)
          (begin (if f? (close-input-port p)) (reverse result))
          (loop (reader p) (cons (proc item) result))))))

(define (fold-input reader proc base . pof)
  (let* ((f? (and (pair? pof) (string? (car pof))))
         (p (cond (f? (open-input-file (car pof)))
                  ((pair? pof) (car pof))
                  (else (current-input-port)))))
    (let loop ((item (reader p)) (base base))
      (if (eof-object? item)
          (begin (if f? (close-input-port p)) base)
          (loop (reader p) (proc base item))))))

(define (read-line . port)
  (define (eat p c)
    (if (and (not (eof-object? (peek-char p)))
             (char=? (peek-char p) c))
        (read-char p)))
  (let ((p (if (null? port) (current-input-port) (car port))))
    (let loop ((c (read-char p)) (line '()))
      (cond ((eof-object? c) (if (null? line) c (list->string (reverse line))))
            ((char=? #\newline c) (eat p #\return) (list->string (reverse line)))
            ((char=? #\return c) (eat p #\newline) (list->string (reverse line)))
            (else (loop (read-char p) (cons c line)))))))

(define (filter-input reader pred?)
  (lambda args
    (let loop ((item (apply reader args)))
      (if (or (eof-object? item) (pred? item)) item
        (loop (apply reader args))))))


; strings

(define (string-index c str)
  (let loop ((ss (string->list str)) (k 0))
    (cond ((null? ss) #f)
          ((char=? (car ss) c) k)
          (else (loop (cdr ss) (+ k 1))))))

(define (string-downcase str)
  (list->string
    (map char-downcase
      (string->list str))))

(define (string-upcase str)
  (list->string
    (map char-upcase
      (string->list str))))

(define (string-split sep str)
  (define (f cs xs) (cons (list->string (reverse cs)) xs))
  (let loop ((ss (string->list str)) (cs '()) (xs '()))
    (cond ((null? ss) (reverse (if (null? cs) xs (f cs xs))))
          ((char=? (car ss) sep) (loop (cdr ss) '() (f cs xs)))
          (else (loop (cdr ss) (cons (car ss) cs) xs)))))

(define (string-join sep ss)
  (define (f s ss)
    (string-append s (string sep) ss))
  (define (join ss)
    (if (null? (cdr ss)) (car ss)
      (f (car ss) (join (cdr ss)))))
  (if (null? ss) "" (join ss)))

(define (string-find pat str . s)
  (let* ((plen (string-length pat))
         (slen (string-length str))
         (skip (make-vector plen 0)))
    (let loop ((i 1) (j 0))
      (cond ((= i plen))
            ((char=? (string-ref pat i) (string-ref pat j))
              (vector-set! skip i (+ j 1))
              (loop (+ i 1) (+ j 1)))
            ((< 0 j) (loop i (vector-ref skip (- j 1))))
            (else (vector-set! skip i 0)
                  (loop (+ i 1) j))))
    (let loop ((p 0) (s (if (null? s) 0 (car s))))
      (cond ((= s slen) #f)
            ((char=? (string-ref pat p) (string-ref str s))
              (if (= p (- plen 1))
                  (- s plen -1)
                  (loop (+ p 1) (+ s 1))))
            ((< 0 p) (loop (vector-ref skip (- p 1)) s))
            (else (loop p (+ s 1)))))))


; sorting

(define sort #f)
(define merge #f)
(let ()
  (define dosort
    (lambda (pred? ls n)
      (if (= n 1)
          (list (car ls))
          (let ((i (quotient n 2)))
            (domerge pred?
                     (dosort pred? ls i)
                     (dosort pred? (list-tail ls i) (- n i)))))))
  (define domerge
    (lambda (pred? l1 l2)
      (cond
        ((null? l1) l2)
        ((null? l2) l1)
        ((pred? (car l2) (car l1))
         (cons (car l2) (domerge pred? l1 (cdr l2))))
        (else (cons (car l1) (domerge pred? (cdr l1) l2))))))
  (set! sort
    (lambda (pred? l)
      (if (null? l) l (dosort pred? l (length l)))))
  (set! merge
    (lambda (pred? l1 l2)
      (domerge pred? l1 l2))))

(define (unique eql? xs)
  (cond ((null? xs) '())
        ((null? (cdr xs)) xs)
        ((eql? (car xs) (cadr xs))
          (unique eql? (cdr xs)))
        (else (cons (car xs) (unique eql? (cdr xs))))))

(define (uniq-c eql? xs)
  (if (null? xs) xs
    (let loop ((xs (cdr xs)) (prev (car xs)) (k 1) (result '()))
      (cond ((null? xs) (reverse (cons (cons prev k) result)))
            ((eql? (car xs) prev) (loop (cdr xs) prev (+ k 1) result))
            (else (loop (cdr xs) (car xs) 1 (cons (cons prev k) result)))))))

(define (vector-sort! vec comp)
  (define-syntax while
    (syntax-rules ()
      ((while pred? body ...)
        (do () ((not pred?)) body ...))))
  (define-syntax assign!
    (syntax-rules ()
      ((assign! var expr)
        (begin (set! var expr) var))))

  (define len (vector-length vec))
  (define-syntax v (syntax-rules () ((v k) (vector-ref vec k))))
  (define-syntax v! (syntax-rules () ((v! k x) (vector-set! vec k x))))
  (define-syntax cmp (syntax-rules () ((cmp a b) (comp (v a) (v b)))))
  (define-syntax lt? (syntax-rules () ((lt? a b) (negative? (cmp a b)))))
  (define-syntax swap! (syntax-rules () ((swap! a b)
    (let ((t (v a))) (v! a (v b)) (v! b t)))))
  (define (vecswap! a b s)
    (do ((a a (+ a 1)) (b b (+ b 1)) (s s (- s 1))) ((zero? s))
      (swap! a b)))

  (define (med3 a b c)
    (if (lt? b c)
        (if (lt? b a) (if (lt? c a) c a) b)
        (if (lt? c a) (if (lt? b a) b a) c)))
  (define (pv-init a n)
    (let ((pm (+ a (quotient n 2))))
      (when (> n 7)
        (let ((pl a) (pn (+ a n -1)))
          (when (> n 40)
            (let ((s (quotient n 8)))
              (set! pl (med3 pl (+ pl s) (+ pl s s)))
              (set! pm (med3 (- pm s) pm (+ pm s)))
              (set! pn (med3 (- pn s s) (- pn s) pn))))
          (set! pm (med3 pl pm pn))))
      pm))

  (let qsort ((a 0) (n len))
    (if (< n 7)
        (do ((pm (+ a 1) (+ pm 1))) ((not (< pm (+ a n))))
          (do ((pl pm (- pl 1)))
              ((not (and (> pl a) (> (cmp (- pl 1) pl) 0))))
            (swap! pl (- pl 1))))
        (let ((pv (pv-init a n)) (r #f)
              (pa a) (pb a) (pc (+ a n -1)) (pd (+ a n -1)))
          (swap! a pv) (set! pv a)
          (let loop ()
            (while (and (<= pb pc) (<= (assign! r (cmp pb pv)) 0))
              (when (= r 0) (swap! pa pb) (set! pa (+ pa 1)))
              (set! pb (+ pb 1)))
            (while (and (>= pc pb) (>= (assign! r (cmp pc pv)) 0))
              (when (= r 0) (swap! pc pd) (set! pd (- pd 1)))
              (set! pc (- pc 1)))
            (unless (> pb pc)
              (swap! pb pc) (set! pb (+ pb 1)) (set! pc (- pc 1)) (loop)))
          (let ((pn (+ a n)))
            (let ((s (min (- pa a) (- pb pa)))) (vecswap! a (- pb s) s))
            (let ((s (min (- pd pc) (- pn pd 1)))) (vecswap! pb (- pn s) s))
            (let ((s (- pb pa))) (when (> s 1) (qsort a s)))
            (let ((s (- pd pc))) (when (> s 1) (qsort (- pn s) s))))))))


; higher-order functions

(define (identity x) x)

(define (constant x) (lambda ys x))

(define (fst x y) x)

(define (snd x y) y)

(define (compose . fns)
  (let comp ((fns fns))
    (cond
      ((null? fns) 'error)
      ((null? (cdr fns)) (car fns))
      (else
        (lambda args
          (call-with-values
            (lambda ()
              (apply
                (comp (cdr fns))
                args))
            (car fns)))))))

(define (complement f) (lambda xs (not (apply f xs))))

(define (swap f) (lambda (x y) (f y x)))

(define (left-section proc . args)
  (lambda xs (apply proc (append args xs))))

(define (right-section proc . args)
  (lambda xs (apply proc (reverse (append (reverse args) (reverse xs))))))

(define-syntax curried-lambda
  (syntax-rules ()
    ((_ () body body* ...)
      (begin body body* ...))
    ((_ (arg arg* ...) body body* ...)
      (lambda (arg)
        (curried-lambda (arg* ...)
          body body* ...)))))

(define-syntax define-curried
  (syntax-rules ()
    ((_ (func arg ...) body body* ...)
      (define func
        (curried-lambda (arg ...)
          body body* ...)))))


; math functions

(define (ipow b e)
  (cond ((zero? e) 1)
        ((even? e) (ipow (* b b) (/ e 2)))
        (else (* b (ipow (* b b) (/ (- e 1) 2))))))

(define (isqrt n)
  (let loop ((x n) (y (quotient (+ n 1) 2)))
    (if (<= 0 (- y x) 1) x
      (loop y (quotient (+ y (quotient n y)) 2)))))

(define (ilog b n)
  (let loop1 ((lo 0) (b^lo 1) (hi 1) (b^hi b))
    (if (< b^hi n) (loop1 hi b^hi (* hi 2) (* b^hi b^hi))
      (let loop2 ((lo lo) (b^lo b^lo) (hi hi) (b^hi b^hi))
        (if (<= (- hi lo) 1) (if (= b^hi n) hi lo)
          (let* ((mid (quotient (+ lo hi) 2))
                 (b^mid (* b^lo (expt b (- mid lo)))))
            (cond ((< n b^mid) (loop2 lo b^lo mid b^mid))
                  ((< b^mid n) (loop2 mid b^mid hi b^hi))
                  (else mid))))))))

(define (expm b e m)
  (define (m* x y) (modulo (* x y) m))
  (cond ((zero? e) 1)
        ((even? e) (expm (m* b b) (/ e 2) m))
        (else (m* b (expm (m* b b) (/ (- e 1) 2) m)))))

(define (halve x) (/ x 2))

(define (double x) (+ x x))

(define (square x) (* x x))

(define (add1 x) (+ x 1))

(define (sub1 x) (- x 1))

(define (logand a b)
  (if (or (zero? a) (zero? b)) 0
    (+ (* (logand (floor (/ a 2)) (floor (/ b 2))) 2)
       (if (or (even? a) (even? b)) 0 1))))

(define (logior x y)
  (cond ((= x y) x)
        ((zero? x) y)
        ((zero? y) x)
        (else
          (+ (* (logior (quotient x 2) (quotient y 2)) 2)
            (if (and (even? x) (even? y)) 0 1)))))

(define (logxor a b)
  (cond ((zero? a) b)
        ((zero? b) a)
        (else
         (+ (* (logxor (floor (/ a 2)) (floor (/ b 2))) 2)
            (if (even? a)
                (if (even? b) 0 1)
                (if (even? b) 1 0))))))

(define (lognot a) (- -1 a))

(define (ash int cnt)
  (if (negative? cnt)
      (let ((n (ipow 2 (- cnt))))
        (if (negative? int)
            (+ -1 (quotient (+ 1 int) n))
            (quotient int n)))
      (* (ipow 2 cnt) int)))

(define (digits n . args)
  (let ((b (if (null? args) 10 (car args))))
    (let loop ((n n) (d '()))
      (if (zero? n) d
          (loop (quotient n b)
                (cons (modulo n b) d))))))

(define (undigits ds . args)
  (let ((b (if (null? args) 10 (car args))))
    (let loop ((ds ds) (n 0))
      (if (null? ds) n
          (loop (cdr ds) (+ (* n b) (car ds)))))))


; random numbers

(define rand #f)
(define randint #f)
(let ((two31 #x80000000) (a (make-vector 56 -1)) (fptr #f))
  (define (mod-diff x y) (modulo (- x y) two31)) ; generic version
  ; (define (mod-diff x y) (logand (- x y) #x7FFFFFFF)) ; fast version
  (define (flip-cycle)
    (do ((ii 1 (+ ii 1)) (jj 32 (+ jj 1))) ((< 55 jj))
      (vector-set! a ii (mod-diff (vector-ref a ii) (vector-ref a jj))))
    (do ((ii 25 (+ ii 1)) (jj 1 (+ jj 1))) ((< 55 ii))
      (vector-set! a ii (mod-diff (vector-ref a ii) (vector-ref a jj))))
    (set! fptr 54) (vector-ref a 55))
  (define (init-rand seed)
    (let* ((seed (mod-diff seed 0)) (prev seed) (next 1))
      (vector-set! a 55 prev)
      (do ((i 21 (modulo (+ i 21) 55))) ((zero? i))
        (vector-set! a i next) (set! next (mod-diff prev next))
        (set! seed (+ (quotient seed 2) (if (odd? seed) #x40000000 0)))
        (set! next (mod-diff next seed)) (set! prev (vector-ref a i)))
      (flip-cycle) (flip-cycle) (flip-cycle) (flip-cycle) (flip-cycle)))
  (define (next-rand)
    (if (negative? (vector-ref a fptr)) (flip-cycle)
      (let ((next (vector-ref a fptr))) (set! fptr (- fptr 1)) next)))
  (define (unif-rand m)
    (let ((t (- two31 (modulo two31 m))))
      (let loop ((r (next-rand)))
        (if (<= t r) (loop (next-rand)) (modulo r m)))))
  (init-rand 19380110) ; happy birthday donald e knuth
  (set! rand (lambda seed
    (cond ((null? seed) (/ (next-rand) two31))
          ((eq? (car seed) 'get) (cons fptr (vector->list a)))
          ((eq? (car seed) 'set) (set! fptr (caadr seed))
                                 (set! a (list->vector (cdadr seed))))
          (else (/ (init-rand (modulo (numerator
                  (inexact->exact (car seed))) two31)) two31)))))
  (set! randint (lambda args
    (cond ((null? (cdr args))
            (if (< (car args) two31) (unif-rand (car args))
              (floor (* (next-rand) (car args)))))
          ((< (car args) (cadr args))
            (let ((span (- (cadr args) (car args))))
              (+ (car args)
                 (if (< span two31) (unif-rand span)
                   (floor (* (next-rand) span))))))
          (else (let ((span (- (car args) (cadr args))))
                  (- (car args)
                     (if (< span two31) (unif-rand span)
                       (floor (* (next-rand) span))))))))))

(define (fortune xs)
  (let loop ((n 1) (x #f) (xs xs))
    (cond ((null? xs) x)
          ((< (rand) (/ n))
            (loop (+ n 1) (car xs) (cdr xs)))
          (else (loop (+ n 1) x (cdr xs))))))

(define (shuffle x)
  (do ((v (list->vector x)) (n (length x) (- n 1)))
      ((zero? n) (vector->list v))
    (let* ((r (randint n)) (t (vector-ref v r)))
      (vector-set! v r (vector-ref v (- n 1)))
      (vector-set! v (- n 1) t))))


; control flow

(define-syntax when
  (syntax-rules ()
    ((when pred? expr ...)
      (if pred? (begin expr ...)))))

(define-syntax unless
  (syntax-rules ()
    ((unless pred? expr ...)
      (if (not pred?) (begin expr ...)))))

(define-syntax while
  (syntax-rules ()
    ((while pred? body ...)
      (do () ((not pred?)) body ...))))

(define-syntax let-values
  (syntax-rules ()
    ((_ () f1 f2 ...) (let () f1 f2 ...))
    ((_ ((fmls1 expr1) (fmls2 expr2) ...) f1 f2 ...)
     (let-values-help fmls1 () () expr1 ((fmls2 expr2) ...) (f1 f2 ...)))))

(define-syntax let-values-help
  (syntax-rules ()
    ((_ (x1 . fmls) (x ...) (t ...) e m b)
     (let-values-help fmls (x ... x1) (t ... tmp) e m b))
    ((_ () (x ...) (t ...) e m b)
     (call-with-values
       (lambda () e)
       (lambda (t ...)
         (let-values m (let ((x t) ...) . b)))))
    ((_ xr (x ...) (t ...) e m b)
     (call-with-values
       (lambda () e)
       (lambda (t ... . tmpr)
         (let-values m (let ((x t) ... (xr tmpr)) . b)))))))


; date arithmetic

(define (julian year month day)
  (let* ((a (quotient (- 14 month) 12))
         (y (+ year 4800 (- a)))
         (m (+ month (* 12 a) -3)))
    (+ day
       (quotient (+ (* 153 m) 2) 5)
       (* 365 y)
       (quotient y 4)
       (- (quotient y 100))
       (quotient y 400)
       (- 32045))))

(define (gregorian julian)
  (let* ((j (+ julian 32044))
         (g (quotient j 146097))
         (dg (modulo j 146097))
         (c (quotient (* (+ (quotient dg 36524) 1) 3) 4))
         (dc (- dg (* c 36524)))
         (b (quotient dc 1461))
         (db (modulo dc 1461))
         (a (quotient (* (+ (quotient db 365) 1) 3) 4))
         (da (- db (* a 365)))
         (y (+ (* g 400) (* c 100) (* b 4) a))
         (m (- (quotient (+ (* da 5) 308) 153) 2))
         (d (+ da (- (quotient (* (+ m 4) 153) 5)) 122))
         (year (+ y (- 4800) (quotient (+ m 2) 12)))
         (month (+ (modulo (+ m 2) 12) 1))
         (day (+ d 1)))
    (values year month day)))

(define (easter year . offset)
  (let* ((a (modulo year 19))
         (b (quotient year 100))
         (c (modulo year 100))
         (d (quotient b 4))
         (e (modulo b 4))
         (f (quotient (+ b 8) 25))
         (g (quotient (+ (- b f) 1) 3))
         (h (modulo (- (+ (* 19 a) b 15) d g) 30))
         (i (quotient c 4))
         (k (modulo c 4))
         (l (modulo (- (+ 32 (* 2 e) (* 2 i)) h k) 7))
         (m (quotient (+ a (* 11 h) (* 22 l)) 451))
         (month (quotient (- (+ h l 114) (* 7 m)) 31))
         (day (+ (modulo (- (+ h l 114) (* 7 m)) 31) 1))
         (q (if (pair? offset) (car offset) 0)))
    (+ (julian year month day) q)))

(define (today) ; Chez Scheme
  (julian
    (date-year (current-date))
    (+ (date-month (current-date)) 1)
    (date-day (current-date))))

(define (today) ; MzScheme
  (let ((today (seconds->date (current-seconds))))
    (julian (date-year today) (date-month today) (date-day today))))


; unit testing

(define-syntax assert
  (syntax-rules ()
    ((assert expr result)
      (if (not (equal? expr result))
          (for-each display `(
            #\newline "failed assertion:" #\newline
            expr #\newline "expected: " ,result
            #\newline "returned: " ,expr #\newline))))))


; miscellaneous

(define (permutations xs)
  (define (rev xs n ys)
    (if (zero? n) ys
      (rev (cdr xs) (- n 1) (cons (car xs) ys))))
  (let ((xs xs) (perms (list xs)))
    (define (perm n)
      (if (> n 1)
          (do ((j (- n 1) (- j 1)))
              ((zero? j) (perm (- n 1)))
            (perm (- n 1))
            (set! xs (rev xs n (list-tail xs n)))
            (set! perms (cons xs perms)))))
    (perm (length xs))
    perms))


Output:
No errors or program output.


Create a new paste based on this one


Comments: