CSC 151.03, Class 08: Testing your procedures

Overview

• Preliminaries
  • Notes and news
  • Upcoming work
  • Extra credit
  • Notes on the quiz
  • Questions
• Lab
• Debrief

News / Etc.

• New places/partners!
• Quizzes returned.
• Homework returned, too (at least for some of you).
• And even some labs.
• I’m still working on catching up. Sorry. “The best laid schemes” and all that.

Upcoming Work

• Writeup for class 7 due TONIGHT at 10:30 p.m.
  • Document take
  • To: csc151-03-grader@grinnell.edu
  • Subject: CSC 151.03 Writeup 7 (YOUR NAMES)
• Assignment 3 due Tuesday.
• Writeup for class 8 due Wednesday at 10:30 p.m.
  • Exercises 3d and 6.
  • To: csc151-03-grader@grinnell.edu
  • Subject: CSC 151.03 Writeup 8 (YOUR NAMES)
• Read: Heterogeneous lists for Wednesdays’s class.
• Read: Representing tables for Wednesdays’s class.

Extra credit (Academic)

• CS Table, Tuesday, noon: Machine Ethics. (Info on Friday’s eboard.)
• CS Extras, Thursday at 4:15 p.m. in 3821. A UI for Chemical Reaction Networks.

Extra credit (Peer)

• ???

Extra Credit (Misc)

• Time Management Workshop, Tuesday, 11am, JRC 226.
• Host a prospie (future)

Other Good Things

• Men’s Soccer vs. Buena Vista, Sept. 17 at 2:00 p.m.

Quiz 2

• Wide distribution of scores, not correlated with prior experience.
• Some struggling with syntax. Some struglling with so many things at so many different levels.

Notes on definitions from part 1

; cat is a procedure that doubles its parameter
(define cat (section * <> 2))
; mouse is a procedure that increments then doubles 
(define mouse (o cat increment))
; The section adds 5
; So moose adds 5 and then computes the square root
(define moose (o sqrt (section + <> 5)))
; squirrel is 11
(define squirrel 11)

Interactions

> squirrel
11
> (mouse 5)
12
> (moose squirrel)
4
> ((section - <> 2) 5)
3
> (map (section - <> 2) (list 1 2 3 4 5))
'(-1 0 1 2 3)
> (5 (section - <> 2)) ; 5 is not a procedure
. . application: not a procedure;
 expected a procedure that can be applied to arguments
  given: 5
  arguments...:
> (map cat (iota 6)) ; (iota 6) => '(0 1 2 3 4 5), cat doubles
'(0 2 4 6 8 10)

Use string-append to define a procedure that takes one input and generates “Hello …. How was your day?”

(define greet
  (lambda (name)
    (string-append "Hello " 
                   name 
                   ". How was your day?")))

With section

(define greet
  (section string-append "Hello " 
                         <>
                         ". How was your day?"))

Questions

Why is there food in the back of the room?

I’m tasked with feeding folks in a once-per-month meeting. I bring my post-meeting class leftovers.

How should we indent?

When you think it would be clearer to see the parameters separated one per line

When your lines are getting really long (> 80 columns)

How much should we indent?

Trust DrRacket.

Ctrl-I reindents.

What are some Ctrl things I should know?

Ctrl-S - Save (it will crash; save early and often)

Ctrl-up-arrow - Previous (escape p)

Ctrl-down-arrow - Next (escape n)

Ctrl-R - Run (the definitions pane)

Ctrl-Enter - Execute current command in interactions pane, even if the cursor is not at the end of the command.

Ctrl-I - reindent

The sections are out of synch

Computers are sentient and malicious, even to your sentient and malicious instructor.

Do we have to document our procedures?

Of course. 4P’s is often okay.

But I turned in my assignment already.

That’s okay, you have another 33 hours or so.

Should we break longer procedures into smaller ones?

Yes, it tends to clarify things.

But I don’t like documenting.

Deal.

What if I give some E’s and some F’s?

Talk to me. (or send me email)

Lab

I’m not quite sure what you want in 3d

Force reload; there’s a hint.

Why did you make us write 13 (epsilon of 2) different explanations in 3d?

Past experience suggests that students don’t think carefully enough about the range of things they might test. Past experience also suggests that if I only ask you to talk through it, you’ll think you get it, but won’t. This one painful exercise is intended to help you think more carefully.

Debrief

Observation: Although Sam suggested test suites, you can put checks directly in your code, and that way you’ll see errors when you click run.

• Yes, that works, too.

Things Sam hopes you took away from today’s class.

• Writing some simple tests is not much harder than just doing experiments,
  • You can write checks even without a test suite.
• On the other hand, writing a comprehensive test suite is hard. You need to think about lots of things that can go wrong.
  • I still write test suites that miss some of the strange things in the code of the folks I am testing.
• That thinking is often helpful, as it lets you reflect more on what the procedure is supposed to do independent of the code you’ve written.
  • Consider writing tests before code.
  • You do so mentally, anyway. “What should my procedure output on an input of 3?”