Is there any documentation on properties of the CallStack object?

Eggplant Functional
1

I’m trying to use theException.CallStack() to print a Java-like stack trace when script caught any exceptions.
I ran

put keys of item 1 of theException.CallStack()

and got

["Handler","HandlerOffset","Line","MeObjectID","MessageName","MessageType","objectType","RepeatIndex","ScriptLine","ScriptObjectID","TargetObjectID","TryDepth"]

Most of them are intuitive, but have some questions. I looked up the documentation of the CallStack function, but there were no explanation of the properties.

  • What does HandlerOffset mean? I see some large numbers like 21541 or 18755.
  • Is Line different from ScriptLine?
  • MeObjectID, ScriptObjectID and TargetObjectID seem to have the same value. Is this expected?
2

HandlerOffset is the offset from the beginning of the script to the beginning of that handler. So a HandlerOffset of 21541 indicates that the handler begins at the 21,541st character of the script.
SenseTalk normally counts lines within each handler, so Line is the handler line number. For convenience when working with editors that show a text line number, we recently added ScriptLine as well which is the line number within the script as a whole.
MeObjectID , ScriptObjectID and TargetObjectID are most often all the same, but can be different if the message was sent to a different target object than the script, or if the script is helping another object. See the documentation on Objects and Messages for more details: Objects and Messages | EPF Docs

3

Hi, @SenseTalkDoug , thanks for the explanation.

As for HandlerOffset, I guessed that was something like that, but I was confused because it was slightly off when opening the script in a text editor. It appears the number does not count the Windows line ending characters (CR-LF) correctly. For example, I had a handler at line 54 of a script and the HandlerOffset was showing 1713, but the actual position was 1764th character (=1713+54) within the script file. Anyway, I don’t need to use it for now, but good to know.

Here is the Java-like stack trace printing snippet I came up with:

Try

    (* code that may throw exceptions *)

Catch theException
    Set printableStackTrace to theException.asText
    Set stacks to theException.CallStack
    Repeat with each item stack of stacks reversed
        If stack.RepeatIndex > 0
            Set stackInfo to Merge("[[newline]]    at [[stack.MeObjectID]]:[[stack.Handler]]:[[stack.Line]] (line [[stack.ScriptLine]]) x[[stack.RepeatIndex]]")
        Else
            Set stackInfo to Merge("[[newline]]    at [[stack.MeObjectID]]:[[stack.Handler]]:[[stack.Line]] (line [[stack.ScriptLine]])")
        End if
        Put stackInfo after printableStackTrace
    End repeat
    LogError printableStackTrace
    Throw theException
End if
4

Interesting point. SenseTalk converts scripts internally to use standard (LF only) line endings. Hence the discrepancy in the HandlerOffset when you use Windows line endings.

Thanks for sharing your code. It’s helpful to see how you are using it, and other people may find it useful. I would suggest using ScriptObjectID rather than MeObjectID, though. In cases where they are different, ScriptObjectID will always identify the script code that is running, and MeObjectID will be some other object that is being helped by this script.

5

Thanks for your valuable suggestion. I changed my code to use ScriptObjectID.