---
title: Eboard 05 Basic types in Racket
number: 5
section: eboards
held: 2019-02-04
link: true
---
CSC 151 2019S, Class 05: Basic types in Racket
===============================================
_Overview_
* Preliminaries
* Notes and news
* Upcoming work
* Extra credit
* Questions
* Important issues
* Lab
Preliminaries
-------------
### News / Etc.
* Happy Monday!
* I've heard some concerning reports from students and mentors in this
course. We'll discuss those before continuing with preliminaries.
* You should have received grades on HW2.
* Ramadan begins during Week 14 this semester. I will do my best to make
appropriate accommodations during week 14 and finals week. College policy
suggests that you must notify me by the end of this week if you need
such accomodations, but I will make them no matter when you notify me.
* The lab writeup links should now be working.
* I apologize for the limited time for Friday's lab. We strive to write
labs that you can finish (or come close to finishing) during class time.
If you don't finish in class time, skim the remaining problems and do
those that you are not confident you can do.
* Warning: Today may be another "too much lab" day.
* Mentor sessions: Wednesday 8-9, Thursday 8-9, Sunday 5-6. CS Commons.
* Our mentors have created a page of useful stuff, available at
and from the reference
menu.
### Upcoming work
* Reading (available online), due before class Wednesday.
* [Pattern matching with regular expressions](../readings/regexp)
* Available tonight.
* [Assignment 3](../assignments/assignment03) due Tuesday night.
* [Flash cards](../flashcards/flashcards03) due Wednesday at 8:00 p.m.
* [Lab writeup](../labs/writeup05) due before class Wednesday.
* Exercise: 6c (the `next-char` procedure)
* Subject: CSC 151.01 Writeup for Class 5 (YOUR NAMES)
* To: csc151-01-grader@grinnell.edu
* Quiz Friday
* Basic types
* Writing procedures
### Extra Credit
#### Extra credit (Academic/Artistic)
* CS Table, Tuesday, Noon, CS Commons: Machine learning and criminal justice.
* Simonite, Tom (2017). How to upgrade judges with machine learning.
MIT Technology Review.
* Angwin, Julia, Larson, Jeff, Mattu Surya, and Kirchner, Lauren.
Machine bias. Pro Publica.
* _Once Upon a Time Wolf_ (tickets required), Bucksbaum.
Friday, 8 February, 7pm.
* _Once Upon a Time Wolf_ (tickets required), Bucksbaum.
Saturday, 9 February, 7pm
#### Extra credit (Peer)
* Home track meet, Saturday, all-day and beyond. (30 min suffices)
#### Extra credit (Wellness)
* HIIT training, 4:30 pm, Tuesday, Dance Studio, Bear. (Cap of two EC units.)
* Hatha Yoga, 7:00 pm, Tuesday, Dance Studo, Bear. (Cap of two EC units.)
#### Extra credit (Misc)
* Leadership Institute info session, Tuesday, 7 p.m. JRC 2nd.
### Other good things
### Questions
Written or electronic flash cards?
> Send me electronic. Choose whatever is better for your studying
for yourself.
For problem 2A, should we generate our own sentence or use the one
you gave us?
> Use the one we gave you.
For problem 2B, should we generate our own templates or use the ones
you gave us?
> It's up to you. The ones we gave you should be good starting points.
For problem 2C, should we generate our own template?
> Definitely.
It appears you screwed up some of the Scheme in the assignment.
> Yup. Let me know and I'll fix it.
How do we get the libraries on our personal computers?
> Start DrRacket
> **File** > **Install Package**
> Enter "https://github.com/grinnell-cs/loudhum.git" (without the quotation
marks).
> Click **Install* or **Update** (whichever appears).
> When the **Close** button becomes available, click it.
Important things
----------------
### Introduction
Background: I have heard from some of you and from some mentors that it
does not seem that you are always treating your partners with respect.
You have different backgrounds in this material and, irrespective of
background, some of you may "catch on" to an idea more quickly than
your partners.
**That does not give you permission to treat your partner as less able,
less valuable, or less competent than you are.**
Everyone in this classroom got into Grinnell. Everyone in this classroom
is capable of doing the material and can contribute usefully to work.
We already had a class code of conduct on the agenda for Friday, but
we need to do some work on those issues today.
Note: Traditionally, the pair programming in CSC 151 is considered a
strength of the course. (There are issues, but we resolve them quickly.)
### Activity
I have handed many of you cards with statements on them. I will ask you
to read those aloud.
### Plans
If you would prefer a partner of the same gender expression on HW4 (or
labs) email me and I'll make sure that happens.
Lab
---
Why do we round x.5 toward even numbers?
> It's a tradition from statistics. Suppose we have a lot of numbers
ending in .5 and we've made the decision to round all of them. If
we round all of them up, the average of our data set is now going to
be higher. If we round all of them down, the average of our data set
is going to be lower. If we round them "toward the even", the average
of our data set should be similar. (This depends on our distribution.)
Why are the numerator and denominator of 1.2 so strange?
> Racket represents inexact numbers (with a decimal point) as fractions
whose denominator is a power of 2, more or less. 1.2 or 6/5, doesn't
have a denominator which is a power of 2, so it does the best it can.
> If we used a denominator of 4, we'd probably write 5/4 (1.25, rather
than 1.2).
> If we used a denominator of 8, we'd probably use 10/8 (1.25 again), which
is better than 9/8 (1.125).
> If we used a denominator of 16, we'd probably use 19/16 (1.1875), which
seems a bit closer.
Which numbers should we use?
Debrief
-------
I forgot: Quizzes returned. You can check the second set of problems on
your own. Let me know if you have questions on the grading.