# Class 15: Homogeneous Lists: Making and Manipulating Groups of Drawings

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This outline is also available in PDF.

Held: Tuesday, 22 September 2009

Summary: Today we explore Scheme's list data structure and some ways to use lists to make interesting images.

Related Pages:

Notes:

• Are there any final questions on Exam 1?
• Today will be a quick overview then mostly lab day.

Overview:

• Context: What and Why Lists?
• Building Lists.
• Mapping Lists.
• Other List Operations.

## Context: What Are Lists?

• Issue: We'd like to make images with lots and lots of similar shapes.
• Problem: How to do so systematically.
• Solution: Scheme's list data structure and some related procedures.

## Building Lists

• `(list val1 val2 ... valn)`
• `(make-list n value)`
• `(iota n)`

## Mapping Lists

• Basic operation: `(map func lst)`>. Apply a function to each element of a list.
• For images, we'll find it easier to do something like
`(map drawing-transform list-of-drawings list-of-values)`

## Other List Operations

• `(append lst1 lst2)` - join two lists
• `(reverse lst)` - just what it sounds like
• `(list-take lst n)` - take the first n elements of a list
• `(list-drop lst n)` - drop the first elements of a list

Back to Documenting Programs and Procedures. On to Anonymous Procedures.

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, 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.