Book Image

Tcl/Tk 8.5 Programming Cookbook

Book Image

Tcl/Tk 8.5 Programming Cookbook

Overview of this book

With Tcl/Tk, you can create full-featured cross-platform applications in a simple and easy-to-understand way without any expensive development package; the only tools required are a simple text editor and your imagination. This practical cookbook will help you to efficiently interact with editors, debuggers, and shell type interactive programs using Tcl/Tk 8. This cookbook will comprehensively guide you through practical implementation of Tcl/Tk 8.5 commands and tools. This book will take you through all the steps needed to become a productive programmer in Tcl/Tk 8. Right from guiding you through the basics to creating a stand-alone application, it provides complete explanation of all the steps along with handy tips and tricks. The book begins with an introduction to the Tcl shell, syntax, variables, and programming best practices in the language. It then explores procedures and the flow of events with control constructs followed by advanced error trapping and recovery. From Chapter 4, a detailed study of string expressions and handling enables you to handle various string functions and use lists to expand the string functionality. The book then discusses in-depth the Tcl Dictionary and how to utilize it to store and retrieve data. File operations and Tk GUI handling are covered extensively along with a developing a real-world address book application to practice the concepts learned.
Table of Contents (20 chapters)
Tcl/Tk 8.5 Programming Cookbook
About the Author
About the Reviewers

Repeating elements

At some point, you may want to populate a list with a number of repeated elements. This may be for testing or various other reasons. To accomplish this, Tcl provides the lrepeat command. The syntax is as follows:

lrepeat number element1 element2 …

How to do it…

In the following example, we will use the lrepeat command to create a list of repeated characters. Return values from the commands are provided for clarity. Enter the following command:

% lrepeat 3 a
a a a

How it works…

The lrepeat command creates a list of the size referenced in the number variable multiplied by the number of elements.

There's more…

In the following example we will combine lrepeat commands to create multiple lists containing repeated characters. Return values from the commands are provided for clarity. Enter the following command:

% lrepeat 3 [lrepeat 3 0]
{0 0 0} {0 0 0} {0 0 0}

As you can see, by combining the lrepeat command we have created a list containing the same element repeated three times...