เรียกใช้ Function อื่น ใน function นั้นๆ ทำยังไงครับ

Function checkDupIndex(prpID,Prefix)
	Dim Rs, genID
	sql = "SELECT * FROM tbl_properties WHERE prp_id='" & prpID & "' "
	Call app.executeSQLDynamicUser(sql,Rs)
	If Not Rs.EOF Then
		genID = Prefix & Right("00000" & (CInt(Right(prpID, 5)) + 5), 5) 
		checkDupIndex(genID,Prefix) 
	Else
		checkDupIndex = prpID
	End If
	
End Function

Function GetNewPropertyID(PrpType)
    Dim Prefix, NewId, Rs, genID
	
	Select Case PrpType
		Case "Rent":
			Prefix = "L"
		Case "Sale":
			Prefix = "S":
		Case "Sale & Rent":
			Prefix = "C"
			PrpType="Sale & Rent"
		Case "SR":
			Prefix = "C"
	End Select
    'Prefix = Left(PrpType, 1)
    'If Prefix = "R" Then Prefix = "L"
    sql = "SELECT Max(prp_id) as ID FROM tbl_properties WHERE rentorsell='" & PrpType & "'"
	Call app.executeSQLDynamicUser(sql,Rs)
    If Not Rs.EOF Then
        If IsNull(Rs("ID")) Then
            genID = Prefix & "00001"
        Else
            genID = Prefix & Right("00000" & (CInt(Right(Rs.Fields("ID").Value, 5)) + 1), 5)    
        End If
    Else
        genID = Prefix & "00001"
    End If
	 Rs.Close
	Set Rs = Nothing 
	
	Call checkDupIndex(genID,Prefix)
	
	
	
End Function