Problem with corrections
When I get a sentence wrong, there are sometimes little pop-ups explaining my mistake. I think this is a really good idea, but in their current form they aren't always very helpful or even accurate. I've noticed two related problems with them:
Only one mistake is corrected.
If the correct sentence was "Eu vou comer uma maçã" and I typed "Eu vou comer um maça", I'd either get an alert about putting masculine "um" instead of feminine "uma", or about leaving off the tilde on the A, but not both.
It sometimes points out things that aren't mistakes.
I think this is happening because my answer is only compared to one of the accepted sentences, but not all of them. For instance "Je suis allé au jardin" and "Je suis allée au jardin" might both be accepted. But if I type "Je suis allée au gardin," my sentence will be compared to the first sentence, and the pop-up will tell me that I should have written "allé", instead of my actual mistake, which was misspelling "jardin".
It's also debatable whether we're given too much leniency or not enough over typos, and whether or not we should lose a heart for leaving off accents. Anyway, like I said, having explanations for our mistakes is a really good idea, but right now there's a lot of room for improvement. What are y'all's thoughts?
Edit: I wish I could provide screenshots to prove my point about "Je suis allée..." but it's hard to get all the different factors to come together correctly without behind-the-scenes knowledge of which translations are accepted for a sentence. I did, however, get this: http://imgur.com/K1rD17F The reason it's wrong is that "au" intrinsically contains "le", since it's a contraction of "à+le", and this popup misleadingly implies that the correct solution should be "au le salon", which would be terrible. It should, in fact, be "dans le salon"--the mistake was that I used the wrong preposition. I do feel like I've proved my point about the popups sometimes being wrong, so I'm going to move this to Troubleshooting, since it's technically a bug report.
Writing code that can detect and correct all errors is probably a mind-boggling complex task. It is probably limited to checking a few things now. In the case of two errors in a single sentence there might not be enough space allocated to provide room for an explanation of more than one error. So the first one that the code detects and thinks it can correct is outputted.
I think showing only one may be a design flaw and a design feature. It is better to show few mistakes so you don't overwhelm the student. Imagine a sentence with 10 mistakes, how exactly will you report that?
Also there is a moral/motivation factor. Showing one mistake may allow a student to come back and fix it, showing 10 mistakes may de-motivate the student. In addition, I believe the "fix my mistake" function will be well suited to resolve that issue, since you can try, fix and it can keep reporting different errors while you correct it.
As for pointing out things that aren't mistakes, there's nothing much you can do there, except report the error. The database may be vast, but it certainly can't cover everything.
Imagine a sentence with 10 mistakes, how exactly will you report that?
They could show at least 2 mistakes without problems: one in a bubble on top and one in a bubble below the sentence.
If there are more than 2 mistakes, I guess those bubbles could overlap which is not good at all. In this case, I can think of two ways:
Repeat the sentence once for every mistake. If there are 3 mistakes, let the sentence be repeated 3 times with one mistake highlighted every time.
Of course, if there are really too many mistakes, it is no good to analyze them all. Maybe the user just typed some nonsense. I'd suggest to accept 2 or 3 mistakes as a maximum to be explained, and if there seems to be more, just show a message like "Oops, this does not looks like the correct answer" or "It seems there are too many mistakes". And, of course, show the correct answer so that the user could analyze their mistakes.
As far as I understand, every type of mistake that Duolingo can explain should be predicted and coded into the sentence as wrong options. I believe the language teams analyze the mistakes we make most often and add the corresponding wrong translations with explanations that have to be shown.
I can see how it might be de-motivating, but I also feel like not pointing out mistakes gives people the impression that they're right, and if you learn to do something wrong the first time it can be harder to relearn it later. I like olimo's solution. But you're right--sending in reports will help. :)
Although this is true, I can offer one instance where it may not always be fruitful. In the programming world, we have some tools called compilers which are used to create software. These tools look through programming code and spew out logical and syntax mistakes. Which is good, however, a missing semi-colon in the programming world, may trigger more than a dozen mistakes which may negatively affect a student because the user often can't tell where the original error is.
That's why I suggested that showing mistakes one by one is sometimes better than many. In your case, I would say you have at least three errors in that small area. The first, is the missing "dans", the second the missing "le", and the third the extra "au". See how it suddenly became more complicated?
I am having similar problems to this on the iPad version. It seems to have gotten worse in a recent update (in the past couple of months) as I'm sure it was more reliable before. The one thing it seems to do most commonly is report that I have made a mistake and to then show a sentence that doesn't have any mistakes indicated in it, which obviously isn't particularly helpful. This seems just like a straight-out bug to me rather than being a limitation of not being able to indicate enough errors.