--- title: Eboard 17 Processing XML number: 17 section: eboards held: 2019-03-04 link: true --- CSC 151 2019S, Class 17: Processing XML ======================================== _Overview_ * Preliminaries * Notes and news * Upcoming work * Extra credit * Questions * XML, revisited * Representing XML in Racket * Expressing patterns in XML * Constructing new documents from old * Lab Preliminaries ------------- ### News / Etc. * Mentor sessions Wednesday 8-9 p.m., Thursday 8-9 p.m., Sunday 5-6 p.m. * Welcome to any prospective students we have. Thank you for bringing warmer weather with you. * I'm back! I hope that you had a good time without me. I apologize for the inconsistency in communication. * I brought you conference swag. (One of each item per person.) ### Upcoming work * Reading for Wednesday * [Forthcoming] * [Assignment 6](../assignments/assignment06) due Tuesday. * [Flash cards](../flashcards/flashcards07) due Wednesday at 8:00 p.m. * Covers Wednesday/Friday/Monday classes * [Lab writeup](../labs/writeup15) due before class Wednesday * Exercises: TBD * Subject: CSC 151.01 Writeup for Class 17 (YOUR NAMES) * To: csc151-01-grader@grinnell.edu * Quiz Friday: Hash tables, structs, and searching XML ### Extra Credit _I would certainly appreciate suggestions of other extra credit activities (preferably via email)._ #### Extra credit (Academic/Artistic) #### Extra credit (Peer) * Grinnell Singers, Sunday at 2pm. with Lyra Baroque Orchestra (professional musicians, period instruments), really difficult pieces by Handel and others. * Twelfth Night this weekend #### Extra credit (Wellness) #### Extra credit (Wellness, Regular) * 30 Minutes of Mindfulness at SHACS every Monday 4:15-4:45 * Any organized exercise. (See previous eboards for a list.) * 60 minutes of some solitary self-care activities that are unrelated to academics or work. Your email reflection must explain how the activity contributed to your wellness. * 60 minutes of some shared self-care activity with friends. Your email reflection must explain how the activity contributed to your wellness. #### Extra credit (Misc) ### Other good things ### Questions _How should we get a hash table into a list form?_ ```drracket > hash '#hash(("Xinya" . 10) ("Sam" . 4) ("Prospie" . 2141) ("Sarina" . 3)) > (define make-entry (lambda (key) (list key (hash-ref hash key)))) > (make-entry "Xinya") '("Xinya" 10) > (map make-entry (hash-keys hash)) '(("Sarina" 3) ("Prospie" 2141) ("Sam" 4) ("Xinya" 10)) ``` _How do I get that in the right order?_ ```drracket > (sort (hash-keys hash) string<=?) '("Prospie" "Sam" "Sarina" "Xinya") > (map make-entry (sort (hash-keys hash) string<=?)) '(("Prospie" 2141) ("Sam" 4) ("Sarina" 3) ("Xinya" 10)) ``` _What is string->lines?_ > I have no idea what you are talking about. Gremlins replaced `file->lines` with that name. And I fixed it. Remember the aphorism, "Computers are sentient and malicious." "And so are CS faculty." _Is there a nice way to convert the structs to something more readable?_ > Maybe ```drracket (struct person (lname fname) #:transparent) (define person->string (lambda (p) (string-append (person-fname p) " " (person-lname p)))) ``` _Something something something proc string. Did that make sense?_ > Um. _Could you tell me more about `for-each`?_ > `(map proc lst)` applies proc to each element of lst, returning a new list. > Sometimes, we have procedures whose only purpose is to have a side-effect, rather than to return something. > If you use those with `map`, you get a list of voids. > For each gives us the side effect without building a useless list. > Demo ```drracket > (for-each (lambda (thing) (hash-set! hash (list-ref thing 0) (list-ref thing 1))) answerers) > hash '#hash(("Mira" . 12) ("Nick" . 1112123) ("Everett" . 55) ("Christa" . 2)) ``` _Wow, you didn't understand me at all. Is there a way to turn the name of a procedure, as a string, into the procedure itself?_ ``` > (foo "square") # ``` _Can I automatically make procedures, just like `struct` does?_ > Not with what you've learned. > Yes, if you're willing to go beyond the scope of the course. _Is there a way to turn a list of lists into a single list?_ > We know that we can turn two lists into one list, with append. ```drracket > (append (range 1 5) (range 2 6)) '(1 2 3 4 2 3 4 5) ``` > If we have a procedure that combines pairs of elements into a single element, we can use `reduce` with a list. ```drracket > (define lol '((a) (b c) (d e f) (a))) > (reduce append lol) '(a b c d e f a) ``` _Can we use `car` and `cdr` and `caddar`?_ > Yes. _Can we use `set!`._ > No!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! XML, revisited -------------- XML is a notation for taking text and marking the type of sections of things, such as the style or such. Closely related to HTML. ```xml

Meanings of Um

Um has many meanings, which is why students use it so much.

Here are some of those meanings.

``` We may want to count or manipulate our HTML/XML documents. * How many paragraphs are there? * How many times does emphasized text appear? * Replace all instances of "Sam" with "$^%%^(&(&*()*" * ... Some can be done with regular expressions, some are hard to do with regular expressions (and may even be impossible). * Suppose we want to count the number of times emphasized text appears (nested or not)? * Suppose we want to count the number of times emphasized text appears within emphasized text. `Computers are really annoying.` How would we do each? If we did not care about nesting, we'd write ``` > (length (regexp-match* "]" str)) ``` For example, ``` > (regexp-match* #px"" text) '("" "" "" "" "") > (define str "Hello there someone") > (regexp-match* #px"" str) '("") > (regexp-match* #px"]" str) '("") > (regexp-match* #px"]" "") '() > (regexp-match* #px"") '("