Dynamic PopupMenu

Dear Forum,

I would like to modify the list contents of a PopupMenu (SelectSection), based on the selections made by another PopupMenu (SelectData). The code below, using ControlUpdate is not working for me. Tried ModifyControl which was also not appropriate. The example below, when case D is chosen the list in the "SelectSection" popupMenu should now include the updated contents of "SectionList".

Anyone with suggestions?

Thanks,
R.

Function Proc_SelectData(PU_Struct) : PopupMenuControl
    STRUCT WMPopupAction &PU_Struct
   
    String sWin = PU_Struct.win
    SetActiveSubwindow $sWin //This activates the subpanel where controls were selected
   
    if(PU_Struct.eventCode == 2) // mouse up           
        Strswitch (PU_Struct.popStr)   
            Case "A":
            break
            Case "B":
            break  
            Case "C":  
            Case "D":
                string quote = "\""
                String/G SectionList = quote + "Second;Third;Fourth;" + quote
                ControlUpdate /W=$sWin SelectSection
                break
            Case "Frequency (Hz)":
            break
            Case "Frequency (bpm)":
            break
            Case "Gap Time":   
            break      
        EndSwitch
    SetActiveSubwindow ## //Go back to parent window
    Else
        Return 0
    EndIF
End
You need to supply a function for populating the popupmenu. This function can then dynamically determine the contents. See DisplayHelpTopic "PopupMenu" and there "Setting The Popup Menu Items/function call".
Thanks Thomas!

I can see how plugging in a function as a value sort of makes sense, but something like  ModifyControl seemed to make more sense. I am sure there is a good reason for this.

Unfortunately I'm getting a compiling error when trying to use the exact code given as example from the help files.
I do not have any other "List" strings in my code that could originate any sort of conflict (even if this is a local string variable) - nonetheless I get a "Unknown/Inappropriate name or symbol" error (??!!).

Check screen-shot attached.

Any idea why this behavior?

Best,
R.
IgorCompileError_0.jpg (690.79 KB) IgorCompileError_0.jpg (690.79 KB)