eval is HTTP:response

I basically want to list the headers that F5 received, and or modified, in an HTTP::response

Okay. Please try this then:

when HTTP_REQUEST {
    set headerlist ""
    foreach x [HTTP::header names] {
        append headerlist "$x = [HTTP::header $x]
"
    }
    HTTP::respond 200 content "Request Headers:
$headerlist"
}

This will send back all of the client's request headers in formatted HTML.