dyoo

#lang racket

(provide count-inversions count-inversions!)

;; A solution to Exercise 2.2d of CLRS.  Counts the number of inversions
;; in a vector of numbers, using a modified merge sort.

;; count-inversions: vector -> number
(define (count-inversions v)
  (count-inversions! (vector-copy v)))

dyoo

#lang racket

;; Implementation of a mergesort on lists, while avoiding intermediate
;; vector construction.  Uses the same trick as that in SICP Exercise
;; 2.64 to keep track of the elements we haven't yet processed.


(provide mergesort)

(define (mergesort elts)

dyoo

#lang racket

(define (in-string/rev s)
  (define stop 'stop)
  (define n (string-length s))
  (define i (sub1 n))
  (define (next!)
    (cond
      [(< i 0)
       stop]

dyoo

#lang racket/base

;; zeller's congruence
;; http://en.wikipedia.org/wiki/Zeller%27s_congruence

(require (for-syntax racket/base)
         racket/unsafe/ops)


;; Gregorian version of Zeller's congruence is:

dyoo

#lang racket/base

;; Gray binary code, from TAOCP 7.2.1.1.
;;
;; Gray codes are sequences where adjacent elements are different in only one position.
;;
;; The gray codes of length n can be generated with the following recursive rules:
;;
;;    G_0 = epsilon
;;    G_{n+1} = 0 G_n, 1 ((G_n)^r)

dyoo

#lang racket

(define (get-first-value f)
  (call-with-values f
                    (lambda the-values
                      (first the-values))))

(get-first-value (lambda () (values 'a 'b 'c)))

dyoo

#lang racket/base

(require ffi/unsafe)

(define (get-errno) 
  (get-ffi-obj "errno" (ffi-lib #f) _int))

dyoo

#lang racket/base

(require xml)

(define an-xexpr
  (xml->xexpr
   (document-element
    (read-xml (open-input-string "<p>hello, this is a &lt;happy&gt; string</p>")))))

an-xexpr

dyoo

> (require data/red-black/ordered-set)
> (define s (new-ordered-set))
> (ordered-set-add! s "hi")
> (ordered-set-add! s "mye")
> (ordered-set-add! s "aloha") 
> (for ([x s]) (printf "this says: ~s" x))
this says: "aloha"this says: "hi"this says: "mye"> (ordered-set-contains?)
ordered-set-contains?: undefined;
 cannot reference undefined identifier
  context...:

dyoo

> (require data/red-black/ordered-set)
> (define s (new-ordered-set))
> (ordered-set-add! s "hi")
> (ordered-set-add! s "mye")
> (ordered-set-add! s "aloha") 
> (for ([x s]) (printf "this says: ~s" x))
this says: "aloha"this says: "hi"this says: "mye"
> (ordered-set-contains?)
ordered-set-contains?: undefined;
 cannot reference undefined identifier