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I am running a program that adds a message to a list after each completed cycle (about 5k cycles). Upon completion, the program saves the list to disk so I can review it.

However, if the program aborts, I lose the list. Can I write an error handler that, with its dying breath, will save that list?

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    $\begingroup$ Have a look at CheckAbort and Catch. $\endgroup$ – Henrik Schumacher Jan 30 '18 at 0:13
  • $\begingroup$ Still, if the kernel crashes, that might be of few use. A safer way would be to write the messages to file every now and then. See, e.g. OpenAppend and friends. $\endgroup$ – Henrik Schumacher Jan 30 '18 at 0:25
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    $\begingroup$ Have you looked at AbortProtect? $\endgroup$ – m_goldberg Jan 30 '18 at 0:52
  • $\begingroup$ I just discovered it. It seems that wrapping everything in 'AbortProtect' and including 'TimeConstrained' would handle a lot. I actually don't see many aborts, the program encounters an error of some in a function that never finishes evaluating. $\endgroup$ – George Wolfe Jan 30 '18 at 0:56
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I think Internal`WithLocalSettings is the tool you want to use. The syntax is:

Internal`WithLocalSettings[
    preliminaryCode, (* can't be aborted *)
    body, (* can be aborted *)
    postprocessCode (* can't be aborted *)
]

Suppose your code looks like:

code[] := (a=1; b=2; Pause[Infinity]; c=3)

and you're interested in the values of a, b and c. Then:

Internal`WithLocalSettings[
    Null,
    code[],
    Print[{a, b, c}]
]

{1,2,c}

$Aborted[]

where I used Evaluation | Abort Evaluation (actually, the shortcut Cmd + .). Note that code[] got aborted, yet the Print statement still occurred, where I use Print as a substitute for some sort of save file utility.

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