Introduction
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## Introduction

“`The question is,' said Humpty Dumpty, `which is to be master - that's all.'”[1]

The IRIS Explorer Module Writer's Guide contains the information you need to master the tools for constructing and installing your own custom-built modules in IRIS Explorer. The options for taking control at different stages of the module-building process are numerous, and you can choose your level according to your current needs.

If your needs are fairly simple, you can take full advantage of the Module Builder's capabilities for automating the process and do very little work yourself, beyond supplying a basic algorithm. On the other hand, you may want to exploit those aspects of the Explorer product that let you as module writer control the process almost entirely.

To let the Explorer program do the work is very convenient, and most of the time it is sufficient, but it does set limits on what you can achieve. To be master yourself takes more effort but offers in return access to all the power and flexibility of the Explorer environment.

## About This Guide

The IRIS Explorer Module Writer's Guide describes how to design and build Explorer modules using the Module Builder.

It provides information about using the built-in Explorer data types and about defining new data types for your particular needs. There are also sections on how to customize your build environment and set up special subdirectories for module development.

This guide is written primarily for programmers who support computational scientists and engineers in the fields of fluid dynamics, chemistry, meteorology, cosmology, physics, and mathematics. It addresses users who will write module suites for other people to use in the Map Editor.

However, any users who wish to extend the functionality of Explorer can write their own modules using the Module Builder.

The guide assumes you:

- can program in either C or Fortran

- understand the UNIX operating system and file structure

- are familiar with the X Window System™ and Motif™

In general, the user interface of the Module Builder adheres closely to the Motif standard.

## Contents of This Guide

The IRIS Explorer Module Writer's Guide has ten chapters and two appendices. They cover the following topics:

- Chapter 1, “Building a Module,” steps the module writer through the module-building process in tutorial form.

- Chapter 2, “Understanding the Module Builder,” explains how to use the Module Builder to create the module resource file.

- Chapter 3, “Using the Lattice Data Type,” describes the lattice data type and explains how it is used in Explorer modules.

- Chapter 4, “Using the Pyramid Data Type,” describes the pyramid data type and explains how it is used in Explorer modules.

- Chapter 5, “Using the Geometry Data Type,” describes the geometry data type and explains how it is used in Explorer modules.

- Chapter 6, “Using the Pick Data Type,”describes the pick data type and explains how it is used in Explorer modules.

- Chapter 7, “Using the Parameter Data Type,” describes the parameter data type and explains how it is used in Explorer modules.

- Chapter 8, “Creating User-defined Data Types,” outlines the Explorer typing language (ETL) syntax and explains how to build user-defined data types.

- Chapter 9, “Advanced Module Writing,” provides information on topics such as hook functions, shared module executables, and reference counting.

- Chapter 10, “Module Prototyping with Shape,” outlines the Shape language syntax and explains how to write Shape scripts for interpreter modules.

- Appendix A, “Using Makefiles,” describes how to create user Makefiles.

- Appendix B, “The Firing Algorithm,” gives an overview of the Explorer execution model.

All the chapters contain sample code and refer the reader to source directories in which modules that use the sample code reside. These modules will run in the Map Editor.

This guide has two companion volumes:

IRIS Explorer User's Guide, which describes the Map Editor and how you launch modules and create maps and applications in it.

IRIS Explorer Reference Pages, which lists all the modules available with Explorer and provides information on the Application Programming Interface (API) routines.

## Conventions Used in This Guide

The IRIS Explorer User's Guide uses the following conventions:

- References to other documents are in italics

- References to other chapters and sections are in “quotation marks”

- Function and subroutine names are in `italics`

- Variable names are in italics

- Names of modules are in `italics`

- Keyboard keys are in `<courier bold>`

- User input is in `courier bold`

- Computer text is in `courier`

- Example code is in `courier`

[1] Through the Looking Glass by Lewis Carroll

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