# Class 40: Variable-Arity Procedures

Back to Tail Recursion, Continued. On to Multiple-Valued Procedures.

Held Wednesday, November 13, 2002

Summary

Today we consider how and why to write procedures that can take different numbers of arguments in different situations.

Related Pages

Assignments

Notes

• Are there any final questions on exam 2?

Overview

• Definition of arity
• Why have variable-arity procedures
• How to write variable-arity procedures
• Lab

## Variable-Arity Procedures

• Def. Arity: The number of parameters a procedure expects.
• Some procedures naturally take varying numbers of parameters:
• `+` takes 0 or more parameters.
• `display` takes 1 or 2 parameters.
• `map` takes 2 or more parameters.
• It would be nice to be able to write our own procedures of variable arity (that is, varying numbers of parameters).
• Zero or more parameters:
```(lambda params
body)
```
• `params` is not parenthesized.
• In your body, treat `params` as a list.
• One or more parameters:
```(lambda (first . remaining)
body)
+ In your body, treating `remaining` as a list.
```
• Two or more parameters:
```(lambda (first second . remaining)
body)
+ In your body, treating `remaining` as a list.
```

## History

Thursday, 29 August 2002 [Samuel A. Rebelsky]

Tuesday, 12 November 2002 [Samuel A. Rebelsky]

• Added a variety of introductory notes.

Back to Tail Recursion, Continued. On to Multiple-Valued 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.

This document was generated by Siteweaver on Mon Dec 2 08:41:54 2002.
The source to the document was last modified on Tue Nov 12 21:47:48 2002.
This document may be found at `http://www.cs.grinnell.edu/~rebelsky/Courses/CS151/2002F/Outlines/outline.40.html`.

You may wish to validate this document's HTML ; ; Check with Bobby

Samuel A. Rebelsky, rebelsky@grinnell.edu