Held: Friday, 27 September 2013

Back to Outline 16 - Homogeneous Lists: Making and Manipulating Groups of Drawings . On to Outline 18 - Turtle Graphics.

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 (Markdown) (HTML) (PDF)

Overview

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

Administrivia

• Welcome to any visiting parents. We've planned the following exciting activities
  • Watch the professor discuss a llong, drawn-out list of administrative issues
  • Watch your students ask questions!
  • Watch your students take a quiz!
  • Watch your students work on a project together
• Note for students: I will not lecture after the quiz. Start the lab once you've finished the quiz.
• Continue lab partners!
  
  • I'm probably moving to switching once per week.
  • After fall break, I may let you choose partners (but may require that you switch once per week).
• I think the optional class was useful for the few folks who showed up. You can see some notes on the EBoard.
  • We won't have the optional class Thursday the 3rd, as I'll be unavailable.
• Work for Monday:
  • Work on the homework assignment
  • Read Turtle Graphics
  • Do Lab writeup 7: Exercise 5b-f from the Anonymous Procedures Lab
    • Due before class on Monday.
    • Title: "CSC 151.02 Lab Writeup 7: Anonymous Procedures (NAMES)".
• A few of you have been confused about lab writeups
  • In general, due the next class.
  • You can find them in every EBoard and outline.
  • I'll work on putting them in the schedule, too.
• EC Opportunities:
  • CS Extras Thursday @ 4:30: Three Students on Student Sysadmin Work
  • CS Table Friday (Coding the Law)
  • Football, 1pm, Saturday against Beloit
  • Orchestra, 2pm, Saturday, Sebring-Lewis or somewhere similar
  • Knitting club, Saturday at 10am. Do good and have fun!
  • More ...?
• Other things you might do (no EC, but possibly a good idea)
  • Swipe your P-Card at the Football or Soccer game
  • Poweshiek CARES March Thursday, Oct. 3. Meet at Drake Library at 5 p.m.
  • GHS Homecoming Parade Thursday, Oct. 3. If you've never seen a small-town homecoming parade, it's worth it.

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.