A function is a program unit containing one or more IDL statements that returns a value. This unit executes independently of its caller. It has its own local variables and execution environment. Referencing a function causes the program unit to be executed. All functions return a function value which is given as a parameter in the RETURN statement used to exit the function. Function names can be up to 128 characters long.
The general format of a function definition is as follows:
FUNCTION Name, Parameter1, ..., Parametern
To define a function called AVERAGE, which returns the average value of an array, use the following statements:
FUNCTION AVERAGE, arr
Once the function AVERAGE has been defined, it is executed by entering the function name followed by its arguments enclosed in parentheses. Assuming the variable X contains an array, the statement,
squares the array X, passes this result to the AVERAGE function, and prints the result. To return the result in a variable, use a function call as follows:
vAvg = AVERAGE(X^2)
Parameters passed to functions are identified by their position or by a keyword. See Using Keyword Parameters. If a function has no parameters, you must specify empty parentheses in the function call.