An Oddity In VIM

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An oddity in vi

I do now know the answer, it was provided quite quickly, and with references to a longer discussion. I intend to write a follow-up to this, with that explanation and my thoughts on it. Still feel free to email me or use the comment box to pass on your thoughts, but as I say, I do now know what's going on.

That doesn't mean I like it ...

I'm going to tell you a story, so this is quite a long post. If you'd like to skip the story get directly to the main point then feel free to do so.

But if you're interested in the story, are you sitting comfortably?

Then I'll begin.

Don't judge me ...

Don't judge me, but I like cricket. There are different forms of the game, and each has its own merits and drawbacks. The problem is that sometimes there's a game I'm interested in, but I only have access to, or time for, a highlights program. And they bounce around so much it can be tricky to keep track of how well each team is doing. I really find it useful when they display the "scoring worm" diagram, but they don't show that as often as I want.

For those who don't know, it won't really matter, but a One Day International (ODI) game usually consists of each team batting once. The bowling team gets a total of 300 "Deliveries" or "Balls" to bowl at them. These are delivered in batches of six, each batch of six is called an "Over" and is delivered by one bowler. A bowler may not deliver consecutive Overs, and each bowler is restricted to at most 10 Overs, so at least 5 different bowlers must be used in a game of 50 Overs.
So I wrote my own.

Of course.

I started by having a file with lines giving:

  • Score, Overs, Balls

I call this a "context" ... it tells us (most of) the current situation, the context of the next ball.

So the program just reads those triples, converts the second and third to a distance along the X axis, the first number into the height, plot that, and we a scoring worm:

To be clear, a team's "Score" is the total accumulation of "Runs". A "Run" can be credited to the team by the batters changing ends (running between the wickets) but also by various penalties due to infringements by the bowler, such as "Wides", "No Balls", and similar. But the "Score" is the accumulation of "Runs".
Here we can see the scoring by Afghanistan on Jan 21${}^{st}$, 2021. They batted first against Ireland, and you can see that I've included lines for scoring at 4, 5, or 6 runs per Over.

You'll also see cross-ticks. They indicate when wickets fall, and since you have to stop batting when you lose ten wickets, there's a balance between taking a risk, trying to score quickly, and running out of batters, versus taking your time, preserving your resource, and possibly running out of time.

It is possible to lose a wicket without the number of balls bowled being advanced, and it's possible to score a run despite a wicket being lost!

No, it's not at all mysterious, but if someone tries to explain it all in dribs and drabs it can give that impression. But in truth, it's all logical and consistent. Or at least, as logical and consistent as any sport can be.

But I needed to be able to put the fall of a wicket in my file. I did that simply by putting a "W" on a line by itself. That could then be proceeded by the context (score/overs/balls), and then when the wicket fell it was implicitly no extra score and one extra ball. So I could put:

    151 29 2
    151 29 3

The third line there isn't strictly necessary, but it makes sense to have it.

More syntax

Sometimes the coverage is really, really annoying, and they don't put the actual score up for minutes at a time, but they do show the runs being scored. So sometimes I know the score at the beginning of an Over, and I know what happens on each ball, so it makes sense to have that as an option. Here's an entire Over from that game:

I now have everything I need to record the "worm" even when there are wides, no-balls, and more. You may choose to think how that's done. When you see it, it's not hard.

    168 35 0
    173 36 0

Compacting the format

The file was starting to become quite long, and I thought it convenient to have the scores from a complete Over all on one line. So the above became this:

    168 35 0
    1 0 1 2 0 1
    173 36 0

Pressing "J" joins "this" line with the next line, with a space (or two!) between them.
In vi (strictly, vim, but I won't quibble) it was easy to score in the longer form, then use "J" multiple times to put all the balls on a single line. The last line isn't strictly needed as it can be deduced from the previous two, but it was no problem, and reflected the scores being reported on the screen in the coverage.

But now we get to our small mystery.

What ?!? Why ???

So I would position the cursor on the line containing the first ball of the Over, then press "J" five times to pull up each of the five other lines to join this one.

"Well," I thought, "vi has the option of putting a multiple in front of a command and it executes the command that many times. So if I type "5J" then it will all happen all at once."

So I typed "5J". Here is the before and after:

168 35 0
173 36 0

168 35 0
1 0 1 2 0
173 36 0


So in this case, pressing J five times does not give the same result as pressing "5J". Instead, one needs to enter "6J", and that seems, to me, completely inconsistent.

My Mental Model ...

I'm getting some feedback, and it looks like:
  • My mental model was wrong;
  • I'm not alone in this;
  • Others have also been surprised;
  • It is "expected behaviour";
  • It's more complicated than you might hope.
I'll update this as more information comes in.
So my mental model of commands in vi is that "nC" is the same as executing "C" n times. But in this case it isn't. So either the internal command interpreter is not what I thought it was, or the designers have explicitly made an exception in this case.

What other exceptions exist? Why should this be an exception at all?

I really just don't understand.

And that is the oddity I found in vi.


Afghanistan won:

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