Programming Capabilities of the IDLDE

The IDL Development Editor (IDLDE) offers you the ability to program applications with ease. The term "IDL Application" is used very broadly and any program written in the IDL language is treated as an IDL application. IDL applications range from the very simple (for example, a MAIN program entered at the IDL command line) to the very complex (for example, large programs with graphical user interfaces). Whether you are writing a small program to analyze a single data set or a large-scale application for commercial distribution, it is useful to understand the programming concepts used by the IDL language. IDL even allows you to call IDL from other programs written in other languages and call other programs from IDL.

Built-In Editor

The IDL Editor is a programmer-style editor. For example, some characteristics include:

Indenting a line using the Tab key also allows following lines to be indented

Using the Shift-Tab key moves position left one tab stop

Moving the cursor position within an IDL Editor window can be done with the mouse or the keyboard

Chromacoded Editor

The Windows IDL Editor supports chromacoding — the automatic coloring of different types of IDL statements. Select File

Preference and choose the Editor tab to display the colors used for different types of entries recognized by IDL.

Types of IDL Programs

There are multiple ways of executing a program within IDL. These involve varying levels of complexity and include:

$Main$

A main program unit consists of a sequence of IDL statements that end in an END statement. Only one main program unit may exist within an IDL project window at any time. All commands (except executive statements) that can be entered at the IDL Command Line can also be contained in an IDL program.

Procedure

A procedure is a self-contained sequence of IDL statements that performs a well-defined task. A procedure is identified by a procedure definition statement where the procedure name is the name of the IDL statement you are creating and the parameters are named variables that are used in the procedure.

Function

A function is a self-contained sequence of IDL statements that performs a well-defined task and returns a value to the calling program unit when it is executed. All functions return a function value which is given as a parameter in the RETURN statement used to exit the function.

Compound Statements

BEGIN...END — Creates a block of statements

Conditional Statements

IF ... THEN ... ELSE — Conditionally executes a statement or a block of statements

CASE — Selects one, and only one, statement for execution

SWITCH — Selects one statement for execution from multiple choices

Loop Statements

FOR...DO — Executes one or more statements repeatedly, while incrementing or decrementing a variable with each repetition, until a condition is met

REPEAT...UNTIL — Repetitively executes a subject statement until a condition is true

WHILE...DO — Executes a statement repeatedly while a condition remains true

Jump Statements

BREAK — Provides a convenient way to immediately exit from a loop statement without resorting to the GOTO statement

CONTINUE — Provides a convenient way to immediately start the next iteration of the enclosing FOR, WHILE, or REPEAT loop

GOTO — Transfers program control to a point in the program specified by the label

Note
For more detailed information about the functions of these IDL statements, see Program Control.