Held: Monday, 29 February 2016

Back to Outline 20 - Collage - Copy and Paste. On to Outline 22 - Images as Functions from Position to Colors.

Summary

We revisit procedures in Scheme. We consider a variety of techniques for writing anonymous procedures, procedures without names.

Related Pages

• Reading: Anonymous Procedures
• Lab: Anonymous Procedures
• EBoard 21 (Source 21)

Overview

• What is a procedure?
• Describing procedures.
• Anonymous procedures.
• Anonymous procedures through lambda expressions.
• Other kinds of anonymous procedures.

Administrivia

• New partners!
• Prof. Curtsinger will be teaching class for the rest of the week.
  • If anyone wants to take notes for eboards, I'll provide extra credit.
• Things I owe you.
  • I will mail you your exams on Tuesday night.
  • I will mail you sample answers to HW4 and HW5 on Wednesday night.
  • I will mail you current grades later in the week.
• Some of you have been asking whether you have to be in class on the day before spring break. I know that the end of the day right before break is a horrible time. You can miss class. However, (a) you should arrange to take the quiz on Thursday and (b) I will still record it as an excused absence.

Reminders

• Office hours this week: M 10-11
  • Sign up at http://rebelsky.youcanbook.me.
  • I'll do a lot of email or text Q&A this week.
• Tutor hours
  • Sunday, 3-5 p.m.
  • Sunday-Thursday, 7-10 p.m.
• Weekly review sessions:
  • Wednesday at 8pm in the CS Commons with
  • No Thursday review session next week .... )-:
  • Thursday at 8pm in the CS Commons with

Upcoming Work:

• Reading for Tuesday
  • Anonymous Procedures
• Assignment 5 due Tuesday at 10:30 p.m.
• Exam 2 to be distributed on Wednsday.
• Lab Writeup: Exercise _
  • Send email titled CSC 151 Lab Writeup 21 (Your Names)
  • Do not include the underscores.
  • Send to CSC151-02-grader@grinnell.edu
  • Due before class on Wednesday.

Extra Credit

• Send your reports to rebelsky@grinnell.edu with subject "CSC 151 Extra Credit". (Do not include the quotation marks.)
• Send opportunities to me before class with subject "CSC 151 EXTRA CREDIT OPPORTUNITY!"

Academic / Artistic

• CS Table, Tuesday, Apple vs. the FBI.
• Met Opera Simulcast, Saturday, March 5.

Peer

• Vote for SGA positions. (Today)

Regular Peer

• Social Dance Workshop Tuesdays 7:00-8:00 in Bucksbaum Dance Studio
• Pun club Saturdays at 4pm in Younker
• Electronic Potpourri on KDIC Fridays at Five
• Space Odyssey KDIC Fridays at Six

Misc

• Christine Tran show in Smith Gallery.
• Thursday evening Pub talk on Plans - Grinnell's own contribution to social media

Far in the Future

• Lords of the Flies, April.

No Extra Credit, But Still Good

What is a procedure?

• One of the basic building blocks of programming.
• Essentially, an encapsulated algorithm
  • Takes some inputs
  • Generates some outputs

Describing Procedures

Traditionally, we write something like

(define *name-of-procedure*
  (lambda (*parameters*)
    *body*))

When applying a procedure, we effectively substitute the arguments we call the procedure on for the parameters in the body, and then evaluate the body.

Anonymous Procedures

• Procedures without names.
• Useful when we just need a procedure once
  • Saves the need to define it (code is more concise)
  • Saves the need to document it
  • Makes code work on its own
• In Scheme, whereever you write a procedure name, you can also write the corresponding lambda expression.
• Very useful with map
• Examples
• ((lambda (x y) (* (+ x y) (- x y))) 2 3)
• (map (lambda (x) (* 5 (+ 1 x))) (iota 10))

Other ways to build anonymous procedures

• Sectioning
• Composition

Lab

• Do the lab.
• Be prepared to reflect.