You can call a function anywhere that you can use an expression, including in number signs (#) in a cfoutput tag, in a CFScript, or in a tag attribute value. One function can call another function, and you can use a function as an argument to another function.

You can call a UDF in two ways:

• With unnamed, positional arguments, as you would call a built-in function
• With named arguments, as you would use attributes in a tag

You can use either technique for any function. However, if you use named arguments, you must use the same argument names to call the function as you use to define the function. You cannot call a function with a mixture of named and unnamed arguments.

One example of a user-defined function is a TotalInterest function that calculates loan payments based on a principal amount, annual percentage, and loan duration in months. (For this function's definition, see A user-defined function example). You might call the function without argument names on a form's action page, as follows:

<cfoutput> 
    Interest: #TotalInterest(Form.Principal, Form.Percent, Form.Months)#
</cfoutput>

You might call the function with argument names, as follows:

<cfoutput> 
Interest: #TotalInterest(principal=Form.Principal, annualPercent=Form.Percent,
    months=Form.Months)#
</cfoutput>