User-Defined Functions

VW Scripting supports defining custom functions within a script. Once defined, a user function can be called just like a built-in function from any expression within the same scripting context.

Defining a Function

A function definition begins with Public or Private followed by Function or Sub, and ends with End Function or End Sub.

Public Function FunctionName(Param1, Param2)
  ' ... function body ...
  Return result
End Function

Keyword	Description
`Public`	The function is callable from expressions outside the script
`Private`	The function is for internal use only
`Function`	Returns a value via `Return`
`Sub`	Does not return a value

Rules:

The first non-blank line of the script must be the function declaration.
The function name and parameters are case-insensitive when called.
Parameters are matched positionally.
All parameters must be provided when calling — no optional parameters.

Returning a Value

Use Return with a value to exit the function and return a result:

Public Function Add(a, b)
  Return a + b
End Function

Use Return with no value (or reach End Function) to exit without a return value:

Public Sub LogMessage(msg)
  Debug(msg)
End Sub

Examples

Simple calculation

Public Function Tax(amount, rate)
  Return amount * rate / 100
End Function

Called as: Tax(Price, 13)

Conditional logic

Public Function Grade(score)
  If score >= 90 Then
    Return "A"
  ElseIf score >= 80 Then
    Return "B"
  ElseIf score >= 70 Then
    Return "C"
  ElseIf score >= 60 Then
    Return "D"
  Else
    Return "F"
  End If
End Function

Called as: Grade(85) → "B"

Using built-in functions inside a user function

Public Function FullName(first, last)
  Return Trim(first) & " " & Trim(last)
End Function

Loop inside a function

Public Function Factorial(n)
  Dim result = 1
  For i = 2 To n
    result = result * i
  Next
  Return result
End Function

Called as: Factorial(5) → 120

Calling a User-Defined Function

Once defined, call the function exactly like any built-in function:

Dim t = Tax(99.99, 13)
Dim g = Grade(Score)

Note: User-defined functions are registered into the same function lookup table as built-in functions. If a user function has the same name as a built-in, the last one registered wins. Avoid naming user functions the same as built-ins.