http-get-shakespeare.scm

;;; Program based on example code from composingprograms.com                                                                  
;;;                                                                                                                           
;;; - Get a text document from the Web containing works of Shakespeare.                                                       
;;; - Count the words in the document and display the result.                                                                 
;;; - Display the list of words that are six-letters long and that written                                                    
;;;   backwards form a word that is also included in the document.                                                            
;;;                                                                                                                           
;;; NOTE: This code takes about 9 minutes to run in my machine. This is                                                       
;;;       because of the delete-duplicates procedure whose execution time                                                     
;;;       is O(n^2).                                                                                                          
;;;                                                                                                                           
;;;       Also note that the list of words obtained with string-split in                                                      
;;;       this case does not include words only but also punctuation marks                                                    
;;;       (the original code from the book does the same).                                                                    

(use-modules (ice-9 receive)
             (srfi srfi-1)
             (web client)
             (web uri))


(define text-url "http://composingprograms.com/shakespeare.txt")
(define words (receive (r-header r-body) (http-get (string->uri text-url))
                       (delete-duplicates (string-split r-body #\space))))
(begin (display (length words)) (newline))

(for-each
 (lambda (word)
   (if (and (= (string-length word) 6) (member (string-reverse word) words))
       (begin (display word) (newline))))
 words)

The problem of time is because of the delete-duplicates procedure that runs in time O(n^2) for n-element lists.