Held: Wednesday, 1 October 2014

Back to Outline 19 - Conditionals. On to Outline 21 - Naming Local Values.

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 (Source) (HTML)

Overview

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

Administrivia

• Keep your partners from yesterday.
• Reminder: You may bring a sheet of notes to Friday's quiz.
• Office hours (modified due to meetings):
  • Thursday 8:00-9:45, 2:30-3:15
  • Friday 2:15-3:15
• Review session Thursday at 10:00 a.m.
• Review sessions Wednesday and Thursday night at 8 p.m.

Upcoming Work

• HW 5 assigned.
• Lab writeup: Conditionals, 3c and 4d http://bit.ly/151-2014F-w19
• Reading for Friday
  • Local Bindings with let

Quiz Topics

Reminder: You may bring a sheet of notes to Friday's quiz.

• Lists (using list, make-list, and iota)
• map
• More simple lambda expressions
• Conditionals
• GIMP procedures (e.g., image-select-rectangle!)
• compose, o, l-s, r-s (the latter two from today's class)

Extra Credit Opportunities

Academic

• CS extras Thursday at 4:30: Alumni
• CS table Friday: Serendipity and Computing (with Grinnell's Artist in Residence)
• Grinnell Prize events the following week (particularly events related to the prize winners whose project involves Web tools)

Peer Support

• Concert tonight.
• Football (???)
• Men's Tennis (???)
• Women's Tennis (???)
• Swimming (???)
• Evan's radio show 5pm Friday nights on KDIC
• Donna's radio show Sunday midnight on KDIC
• Anna Christie, Oct. 9-12 (SB plays Marthy)

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.