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Interesting Matlab puzzle

March 31, 2019 20 Comments

Here’s a nice little puzzle that came to me from long-time Matlab veteran Andrew Janke:
Without actually running the following code in Matlab, what do you expect its output to be? ‘Yaba’? ‘Daba’? perhaps ‘Doo!’? or maybe it won’t run at all because of a parsing error?

function test
    try
        if (false) or (true)
            disp('Yaba');
        else
            disp('Daba');
        end
    catch
        disp('Doo!');
    end
end

function test try if (false) or (true) disp('Yaba'); else disp('Daba'); end catch disp('Doo!'); end end

To muddy the waters a bit, do you think that short-circuit evaluation is at work here? or perhaps eager evaluation? or perhaps neither?
Would the results be different if we switched the order of the conditional operands, i.e. (true) or (false) instead of (false) or (true)? if so, how and why?
And does it matter if I used “false” or “10< 9.9” as the “or” conditional?
Are the parentheses around the conditions important? would the results be any different without these parentheses?
In other words, how and why would the results change for the following variants?

        if (false) or (true)     % variant #1
        if (true)  or (false)    % variant #2
        if (true)  or (10< 9.9)  % variant #3
        if  true   or  10< 9.9   % variant #4
        if 10> 9.9 or  10< 9.9   % variant #5

if (false) or (true) % variant #1 if (true) or (false) % variant #2 if (true) or (10< 9.9) % variant #3 if true or 10< 9.9 % variant #4 if 10> 9.9 or 10< 9.9 % variant #5

Please post your thoughts in a comment below (expected results and the reason, for the main code snippet above and its variants), and then run the code. You might be surprised at the results, but not less importantly at the reasons. This deceivingly innocuous code snippet leads to interesting insight on Matlab’s parser.
Full marks will go to the first person who posts the correct results and reasoning/interpretation of the variants above (hint: it’s not as trivial as it might look at first glance).
Addendum April 9, 2019: I have now posted my solution/analysis of this puzzle here.

USA visit

I will be travelling in the US (Boston, New York, Baltimore) in May/June 2019. Please let me know (altmany at gmail) if you would like to schedule a meeting or onsite visit for consulting/training, or perhaps just to explore the possibility of my professional assistance to your Matlab programming needs.

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Recent Comments
  • Iñigo (2 days 9 hours ago): Thanks Yair. I didn’t realize it was posted just above. It would be great to know about a solution soon
  • Yair Altman (3 days 16 hours ago): @Iñigo – your query is related to Seth’s question above. We can access the currently-browsed URL in JavaScript (for example: jBrowserPanel.executeScript...
  • Iñigo (5 days 8 hours ago): I am looking for setting a UI that allows following process: opening a web site, navigate inside this web site and at some specific moments (i.e. when the figure is closed or a button...
  • Nicholas (12 days 14 hours ago): Yair, this works wonderfully! I can’t thank you enough!
  • Collin (14 days 17 hours ago): Seth Good point, I am using 2022b, mathworks seems to have started using CEF browsers from 2019a, best I can tell. take a look at the package com.mathworks.toolbox.matla...
  • Seth (15 days 9 hours ago): Collin, What version of MATLAB are you using?
  • Collin (20 days 16 hours ago): Seth, I have had some success executing javascript that requires no return value by executing it directly (sort of) on the org.cef.browser.CefBrowser that a...
  • Coo Coo (22 days 11 hours ago): FFT-based convolution is circular whereas MATLAB’s conv functions have several options (‘valid’, ‘same’, ‘full’) but unfortunately not...
  • Seth (22 days 14 hours ago): No luck with removing the space.
  • Seth (22 days 15 hours ago): The javascript code works fine running the application from the 2019b desktop version and the 2016b deployed version.
  • Seth (22 days 15 hours ago): I have been using this browser functionality in 2016b because it works fully in deployed applications in that version. However, because of Java 7 being flagged as a security risk, I...
  • Yair Altman (22 days 15 hours ago): I’ve never tested javascript callbacks, but perhaps you should try removing the extra space after the “matlab:” protocol specifier. Does it make any difference?
  • Seth (22 days 16 hours ago): I have been using this functionality in 2016b since it works in deployed applications and have not had a reason to need to upgrade but with java 7 being flagged as a security risk I am...
  • KEVIN (42 days 17 hours ago): I apologize, I intended my response to fall under ‘T’ but did not seem to work. I was referring to the bit of code posted by ‘T’ regarding the toolgroup and...
  • Yair Altman (42 days 17 hours ago): It is not clear from your comment which code exactly you are referring to and what you see differently in 19b vs. 20b, so I cannot assist with your specific query. In general I...
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