Class 16: Anonymous Procedures

Back to Homogeneous Lists: Making and Manipulating Groups of Drawings . On to Turtle Graphics.

This outline is also available in PDF.

Held: Wednesday, 23 September 2009

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

Related Pages:

Notes:

The department is sponsoring a talk on A Historical View of the Early Development of Programming Languages on Friday, Oct. 2, at noon. Free pizza. We need an approximate head count. Is anyone interested in coming? EC for attending.
Reading for Friday: Turtle Graphics. Yes, we're starting yet another perspective on images. We'll count how many we have so far.
In the future, please do not hand in the printed copy of your exam until the day it is due.
We had at least one student lose work because MediaScheme crashed while they were working. Your generation should know to Save early and often!
The next assignment should be ready tomorrow afternoon. Sorry for the delay.
No introductory lecture today!

Overview:

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

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 (define name-of-procedure (lambda (parameters) body))
When applying one of these, 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!

Back to Homogeneous Lists: Making and Manipulating Groups of Drawings . On to Turtle Graphics.

[Skip to Body]
Primary: [Front Door] [Schedule] - [Academic Honesty] [Instructions]
Current: [Outline] [EBoard] [Reading] [Lab] - [Assignment]
Groupings: [Assignments] [EBoards] [Examples] [Exams] [Handouts] [Labs] [Outlines] [Projects] [Readings]
References: [A-Z] [By Topic] - [Scheme Report (R5RS)] [R6RS] [TSPL4]
Related Courses: [CSC151.02 2009S (Weinman)] [CSC151.02 2009S (Davis)] [CSC151 2008S (Rebelsky)]
Misc: [SamR] [MediaScript] [GIMP]

Disclaimer: I usually create these pages on the fly, which means that I rarely proofread them and they may contain bad grammar and incorrect details. It also means that I tend to update them regularly (see the history for more details). Feel free to contact me with any suggestions for changes.

This document was generated by Siteweaver on Fri Dec 11 09:38:42 2009.
The source to the document was last modified on Fri Aug 21 17:03:06 2009.
This document may be found at http://www.cs.grinnell.edu/~rebelsky/Courses/CS151/2009F/Outlines/outline.16.html.

You may wish to validate this document's HTML ; ;

Samuel A. Rebelsky, rebelsky@grinnell.edu

Copyright © 2007-9 Janet Davis, Matthew Kluber, Samuel A. Rebelsky, and Jerod Weinman. (Selected materials copyright by John David Stone and Henry Walker and used by permission.) This material is based upon work partially supported by the National Science Foundation under Grant No. CCLI-0633090. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation. This work is licensed under a Creative Commons Attribution-NonCommercial 2.5 License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc/2.5/ or send a letter to Creative Commons, 543 Howard Street, 5th Floor, San Francisco, California, 94105, USA.