--- title: Eboard 29 Files in Scheme number: 29 section: eboards held: 2017-11-06 --- CSC 151.01, Class 29: Files in Scheme ====================================== _Overview_ * Preliminaries * Notes and news * Upcoming work * Extra credit * Questions * Review of hop * Lab * Debrief ### News / Etc. * Sorry about the Website weirdness on Friday. The style sheet that I rely on changed significantly. * Sorry that I could not be in class on Friday. * No, grading is not done. Thursday, Friday, Saturday, and half of Sunday were booked. I spent six hours grading, but that's not enough. * Tonight is "Write 301 exam and write 151 project", so no grading will get done. * * It's preregistration week. I encourage you to consider CSC 161. (Weinman and Walker are both responsible graders.) ### Upcoming Work * [Writeup for class 28](../writeups/writeup28) due Monday at 10:30 p.m. * Exercise 5. (No documentation necessary, but appreciated.) * To: * Subject: CSC 151.01 Writeup 28 (YOUR NAMES) * [Writeup for class 29](../writeups/writeup29) due Wednesday at 10:30 p.m. * Exercise 6. No documention necessary. * To: * Subject: CSC 151.01 Writeup 29 (YOUR NAMES) * Read [Analyzing algorithms](../readings/analysis) for Wednesday's class. * No, it's not ready. * [Exam 3](../exams/exam03) distributed. * Prologue due Friday. * Exam due Tuesday the 14th. * Cover pages due Wednesday the 15th. * Epilogues due Wednesday the 15th. ### Extra credit (Academic/Artistic) * Leyla McCalla Trio, Nov. 6, 7:30 p.m. Herrick * Animated Films, Tuesday, Nov. 7, 11:00 a.m., Faulconer * CS Table (Computer-Aided Gerrymandering), Tuesday, Nov. 7, noon, Day Dining Room * Crip Technoscience, Disabled People as Makers and Knowers, Wednesday, Nov. 8, 4:15 p.m., JRC 101. ### Extra credit (Peer) ### Extra credit (Misc) * Pioneer Weekend, this coming weekend. Design a business idea (can be a nonprofit / for social good) have fun, get advice, and make money. * Sign up by Nov. 8. ### Other good things ### Questions Review of higher-order programming ---------------------------------- What did we learn on Friday? * Ways of combining procedures. * `l-s`, that procedure that E hates. * `(l-s proc val)` == `(section proc val <>)` * Note: We can write `l-s` * We learned `apply`, which is kind of like `map` and kind of like `reduce`, but different. * We can write procedures that take another procedure as a parameter. * Procedure parameters look like normal parameters. * We just use them in the "context" of procedures. If f is a parameter, we can write (f 1) or (map f (iota 5) or .... * We can write procedures that return another proceudre as a result. * Most typically, use a second lambda to define/return the new procedure. Lab --- Why am I able to read a file in your account? : I set permissions that way. (Linux lets you set permissions on files in your account so that others can read them. There are a variety of options. You'll learn how to do so in CSC 161.) How do I "create a file in the interactions pane"? : `(define outport (open-output-file "/home/username/Desktop/myinfo"))` How do I write to that file? : `(write stuff outport)` : `(display stuff outport)` : `(newline outport)` What should I do when I'm done? : `(close-output-port outport)` How should I overwrite an existing file : `(define outport (open-output-file "/home/username/Desktop/myinfo" #:exists 'replace))` <<<<<<< Updated upstream Writeup: Exercise 6. Reload the lab before doing it. ======= Writeup: Exercise 6 >>>>>>> Stashed changes Debrief ------- How did you figure out that the sum was correct? : `(apply + (map string->number (file->words FILE)))` : Open the file in DrRacket. Put `(+` at the start. Put ')' at the end. Evaluate. : Open the file in a spreadsheet and use the spreadsheet sum. An incomplete definition of `file-size`. ``` (define file size (lambda (file-name) (let ([source (open-input-file file-name)]) (let kernel ([size-so-far 0]) (let ([nextval (read-char source)]) (cond [(eof-object? nextval) (close-input-port source) size-so-far] [(char? nextval) (kernel (+ nextval size-so-far))] [else (kernel size-so-far)])))))) ``` Problem: `nextval` can be the eof object or a character, and nothing else. So ... ``` (define file size (lambda (file-name) (let ([source (open-input-file file-name)]) (let kernel ([size-so-far 0]) (let ([nextval (read-char source)]) (cond [(eof-object? nextval) (close-input-port source) size-so-far] [(char? nextval) (kernel (+ nextval size-so-far))] [else (kernel size-so-far)])))))) ``` Note: By default, you can only read from existing files and write to new files. ``` (define do-with-all (lambda (proc lst) (when (not (null? lst)) (proc (car lst)) (do-with-all proc (cdr lst))))) ```