A bit of MATLAB syntax fun

Just now, instead of executing the following code at the command line

>> x = 7;
>> x >= 5

I did the following typo:

>> x = 7;
>> x >- 5

Can you guess what the output was?

[Walter Roberson]

Interesting. So command/function equivalence does not look for variables with the given name.

Answer 1

[Matt J]

Unrecognized function x?

Answer 2

[Image Analyst]

I'd say true. I think it ignores the space between the negative sign and the 5 and 7 is greater than -5 so the answer is true.

[the cyclist]

This is what happens in PostgreSQL, which is where I actually made this typo (and was surprised that it was not just a syntax error). It took me a little while to figure out that it was interpreting it as a unary minus sign.

Then I tried it out in MATLAB, and was again surprised at the result! (But it didn't take me as long to figure out what was going on.)

Answer 3

[Jan]

No, I cannot guess it.

I'm even astonished, that copy&pasting ">> x = 7;" works inspite of the ">>". Is this documented?

By the way, see https://www.mathworks.com/matlabcentral/answers/1759-dumb-mistakes-we-make-with-matlab#answer_284120

[the cyclist]

Sorry for the confusion. I only meant to represent that I was at the command line. I did not type the >>.

Also, I wanted to obscure the editor giving a clue to the answer:

x = 7;
x >- 5

[Jan]

Matlab's tries to guess smartly, what the user meant. Allowing the non-functional form of commands must cause ambiguities. I ran into troubles sometimes, when this interpretation changes between versions and in consequence I avoid this in productive code. I even write

axes('NextPlot', 'add')

instead of the fragile

hold on

[Image Analyst]

I've never had trouble with hold on, and haven't noticed any difference in that from version to version. So, in my experience, it has not been "fragile".

[Jan]

@Image Analyst: Yes, you are right. My formulation was misleading. hold on is not and have not been fragile. I meant other command using non-functional forms.

See: https://www.mathworks.com/matlabcentral/answers/1680-what-parts-of-matlab-would-you-not-miss#comment_3143

fullfile * *  % Working:

ans = '*/*'

fullfile * p  % Error:

Error using fullfile
Not enough input arguments.

I had a longer list posted in the forum, which I add here, if I find it. The interpretation of the non-functional form did change between some releases. Therefore I avoid the non-functional form although it is expected, that e.g. "hold on" will work reliably. After being tricked too often, I got stubborn.

[the cyclist]

Responding to your first comment, @Jan ... I had forgotten about the Dumb Mistakes thread, but I'm proud that I had the most-upvoted answer!