Fundamentals of Computer Science I: Media Computing (CS151.01 2008S)

Class 18: Iterating Over Lists

Back to Conditionals. On to Naming Local Values.

This outline is also available in PDF.

Held: Wednesday, 20 February 2008

Summary: We consider procedures for that involve doing something with each element of a list. Along the way, we consider two key ideas of functional programming: higher-order programming and anonymous procedures .

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Review: How Scheme evaluates expressions

Let's consider the steps involved in evaluating

(define x 5)
(define y 3)
(+ x y)

Now, let's try the following somewhat more complicated example.

(define x 5)
(define y 7)
(define fun (lambda (x) (* x y)))
(fun 3)


Building new lists from old with map

Anonymous procedures

Let's return to the examples. What happens if we write

(define triple (lambda (x) (* x 3))))
(map triple (list 1 2 3))

As we'll see, the interpreter substitutes the lambda expression for the triple. We can do the same.

(map (lambda (x) (* x 3)) (list 1 2 3))

Doing something with each value in a list with foreach!

Back to Conditionals. On to Naming Local Values.

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.

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Samuel A. Rebelsky,

Copyright © 2007-8 Janet Davis, Matthew Kluber, and Samuel A. Rebelsky. (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 or send a letter to Creative Commons, 543 Howard Street, 5th Floor, San Francisco, California, 94105, USA.