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Thanks, ww, for the detailed critique. The pickier the better!
... blows up...
<i>Now it blows up!</i> is italicized. We need to investigate if it doesn't show up that way for all. I used the phrase 'blows up' twice, in early attempt to show the newcomer sympathy with his viewpoint (likely, just shy of hysteria). Later I try to wean the newcomer onto orthodox concepts: '... die: the program exits with a fatal error...' but at the start I feel this too cold. Perhaps once is enough for metaphorical explosives:
This is of course technically untrue; the code does do something. But KISS.
... the error message tells you where...
To anyone with even a little debugging experience, where is the most important question: where it do go blooey dammit?? That's where the search for something to change begins, the first clue in a fault hunt. Sometimes the fault is rightthere; sometimes it's far away; but we do generally start looking at the indicated FILE and LINE. So why don't I emphasize this?
This tutorial assumes that the reader is a raw newcomer who has just now, for the first time, added use strict; to some code. I have spent quite a lot of time working with youngsters who encounter academic difficulty. These are kids whose solution, literally, for flat bicycle tire is buy new tire. Having seen the result of enforcing strictures, the intended audience of this tutorial will immediately think to remove the line that "caused the problem". I feel convincing the newcomer to retain strictures at all is most important.
After inserting use strict; the next step is to begin debugging and not to delete the "offending" line. Showing how to find and correct the actual fault in newcomer's code is not really in scope of this tutorial.
I do agree that this paragraph needs more work. I'll try some different stuff and see what I can improve.
Strict Errors... one or more lines after the actual mistake...
Sorry; but I think I'd rather go the other way and delete altogether:
Art of Debugging is a mere taste but does cover this ground (in its proper place): Start with the first file name and line number given; check that line carefully. You may have to work backwards from there. I should use Strict Errors only to show the newcomer how to recognize that an error message is, indeed, a stricture error. Perhaps I should stick to the concrete examples.
... the "Reason" subhead...
Reason: and Why: are redundant and lack focus. I'll see if I can't reorganize the examples so that each has only a single Why: section that explains clearly the fault in the example code. For all three examples, these sections are weak.
... bareword... subs first...
Agreed. The example is contrived; the raw newcomer is unlikely to be passing callbacks around. More likely is invocation of a subroutine before it's been declared. I'll try that.
...# comment out to avoid errors...
Agreed; a very poor choice on my part. I think I was wrong to suggest at all that the newcomer comment out use strict;. Rather, I should deploy the demo with it already commented out and invite the newcomer to activate it and enjoy the sauce.
Also, ww, your "tiny nitpicking" leads to an important issue with the entire demo: The examples of "bad" code work just as well, without strictures, as the "good" code works with. So the demo does not demonstrate any value for strictures.
I'm going to work over all the examples. For each example:
I hope this is feasible.
I'm not the guy you kill, I'm the guy you buy. —Michael Clayton