Stop NotebookEvaluate before the end of a notebook depending on test inside this notebook

Question

CONTEXT:

Hello,

I have 2 notebooks, lets call them "Main.nb" and "FileProcessing.nb". In my "Main.nb" I have a Do loop where the iterating parameter goes over 300 .csv files which I want to process. I wrote the code for the processing into the "FileProcessing.nb".

However not every .csv file is in the right format - e.g. sometimes something is missing, hence the file is too short. I wrote tests into the "FileProcessing.nb", so as it is evaluating it can at several moments discover problems (= a test return False). In such case I want to stop evaluating the "FileProcessing.nb" and continue the Do loop in "Main.nb" with next value of the parameter.

QUESTION:

Is there a way, how can I at several points in the "Fileprocessing.nb" decide if I want to proceed or to stop and continue in the Do loop in "Main.nb"?

TOY PROBLEM:

I have the "Main.nb" and "FileProcessing.nb" in the same folder. The "Main.nb" contains

dir = SetDirectory[NotebookDirectory[]]

Table[
 NotebookEvaluate[FileNameJoin[{dir, "FileProcessing.nb"}]],
 {filenumber, 4}
]

and the "FileProcessing.nb" contains

Print["Hello world! ", 100 + filenumber]

Return["Succesfully returned."]

If[
 filenumber < 3,
 Print["Test OK."],
 Print["Too big."]; Return["Stopped."]
 ]

Print["Hallo Welt! ", 100 + filenumber, "\n"]

There is Return on the second line, so rest of the code does not evaluate. It prints fourtimes "Hello world!" with number (101-104) in the "Main.nb" and returns table with fourtimes "Succesfully returned.".

As far, it behaves as I expected. It is "the proof" that Return[] works. However, I want to return only if something "bad" happends (= a test returns False). So if you remove the second line Return["Succesfully returned."], then there is Return inside If. The idea is that if the test filenumber < 3 is false, the rest of the notebook content should not be evaluated. But Return inside If means in fact something different. It does not return from the whole notebook, but only from the If statement and the rest of the code is always executed.

When I realised that, I tried to wrap NotebookEvaluate in Catch and instead of Return use Throw, but it does not work. It gives the following error

Throw::nocatch: Uncaught Throw[Stopped.] returned to top level.

Then I found in "NotebookEvaluate" documentation page that "The cells of the notebook are evaluated in a dialog subsession.", but I have not been able to use this information to my advantage...

PS: I use version 11.3 and at home (where I write this question) I have 12.1.

I would be very grateful for any help and guidance.

Answer 1

This looks like a good place to use Throw and Catch. Try this FileProcessing.nb :

Print["Hello world! ", 100 + filenumber]

(*Return["Succesfully returned."]*)

Return[Catch[

  If[filenumber < 3,
    Print["Test OK."]; Throw["Success."],
    Print["Too big."]; Throw["Failed."]
   ];

  Print["Hallo Welt! ", 100 + filenumber, "\n"]

 ]]

The result in Main.nb is

Hello world! 101
Test OK.

Hello world! 102
Test OK.

Hello world! 103
Too big.

Hello world! 104
Too big.

{"Success.", "Success.", "Failed.", "Failed."}

Importantly, Throw stops evaluation and returns its argument to the nearest Catch, so you may not want to Throw["Success"] until after all of your If statements.