Defender XDR KQL Function that converts query results to markdown doesn't work

Question

I created this saved function in MDE Advanced Hunting (saved as TableToMarkdown) that is intended to convert ingested query results into markdown language:

let TableToMarkdown = (T:(*)) {
    let schema = T | getschema;
    let headers = schema | project ColumnName | summarize make_list(ColumnName) | extend String = strcat('| ', strcat_array(list_ColumnName, ' | '), ' |') | project String, Order=1;
    let upperDivider = schema | project ColumnName, Sep = '---' | summarize Cols=make_list(Sep) | extend String = strcat('| ', strcat_array(Cols, ' | '), ' |') | project String, Order=2;
    let data = T | extend Cols=pack_array(*) | extend String = strcat('| ', strcat_array(Cols, ' | '), ' |') | project String, Order=3;
    headers 
    | union upperDivider
    | union data
    | order by Order asc 
    | summarize Rows=make_list(String) 
    | project array_strcat(Rows, '\r\n')
}

Sample output:

| Timestamp | DeviceName | ActionType | AdditionalFields |
| --- | --- | --- | --- | --- |
| 2024-07-22T01:18:08.0515724Z | MyHostName | UsbDriveMounted | {"DriveLetter":"D:","BusType":7,"ProductName":"CDDVDW GP70N    ","ProductRevision":"RR01","SerialNumber":"ABCDEFG123","Manufacturer":"hp","Volume":"\\\\?\\Volume{270-02-11b-92-863}","LoggedOnUsers":["USERNAME"]} |
| 2024-07-22T13:03:57.4174787Z | MyHostName | UsbDriveMounted | {"DriveLetter":"E:","BusType":7,"ProductName":"DVDRAM GP65NB60 ","ProductRevision":"PF00","SerialNumber":"ABCDEFG124","Manufacturer":"HL-DT-ST","Volume":"\\\\?\\Volume{2a0-3d-df3-11-3f4}","LoggedOnUsers":["USERNAME"]} |

The intent is to use it by piping query results into the function, like so:

let Sus_HostName = 'MyHostName';
DeviceEvents
    | where DeviceName has Sus_HostName
    | where ActionType contains "USB"
    | invoke TableToMarkdown()

However, I keep running into this error whenever I run that query, or add | invoke TableToMarkdown() to any query:

Syntax error

Error message
Expected: ;

How to resolve
Fix syntax errors in your query

Token
}

Line
1

Position
2

The only way I can get the function to work is to store the query as a variable and include the entire function in the query, like so:

let Sus_HostName = 'MyHostName';
let t = DeviceEvents
    | where DeviceName has Sus_HostName
    | where ActionType contains "USB";
let schema = t | getschema;
let headers = schema | project ColumnName | summarize make_list(ColumnName) | extend String = strcat('| ', strcat_array(list_ColumnName, ' | '), ' |') | project String, Order=1;
let upperDivider = schema | project ColumnName, Sep = '---' | summarize Cols=make_list(Sep) | extend String = strcat('| ', strcat_array(Cols, ' | '), ' |') | project String, Order=2;
let data = t | extend Cols=pack_array(*) | extend String = strcat('| ', strcat_array(Cols, ' | '), ' |') | project String, Order=3;
headers 
    | union upperDivider
    | union data
    | order by Order asc 
    | summarize Rows=make_list(String) 
    | project array_strcat(Rows, '\r\n')

 

I'm kinda new to Defender XDR so this is making my head spin. What am I doing wrong or not understanding? For simplicity's sake, I would like to be able to just add | invoke TableToMarkdown() or something similar to the ends of my queries if at all possible.