# Class 18: Recursion Basics

Back to List Iteration Lab. On to Tail Recursion.

This outline is also available in PDF.

Held: Friday, 28 September 2007

Summary: We begin our exploration of recursion, the most general form of repetition available in Scheme. You can use recursion to both build and iterate over different kinds of values. Today, we explore how you use recursion to build simple numeric values from lists, and how to remove elements from lists.

Related Pages:

Notes:

• Assignment 8 is now available (and due Tuesday).
• We'll try something different today: We'll start with lab. I will go over the key ideas in Monday's class.
• But yes, there is a reading for Monday. It's about a different kind of recursion, tail recursion.
• Extra Credit for going to the Science Poster Session on Saturday, and seeing Amanda M's poster, or Emily's poster, or anyone else in the class's poster.

Overview:

• The idea of recursion.
• A sample recursive procedure: `sum`.
• Another exmaple: Filtering.

Back to List Iteration Lab. On to Tail Recursion.

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 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 `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.