On Thu, 13 Oct 2022 at 11:19, Peter J. Holzer <hjp-pyt...@hjp.at> wrote: > > On 2022-10-11 09:47:52 +1100, Chris Angelico wrote: > > On Tue, 11 Oct 2022 at 09:18, Cameron Simpson <c...@cskk.id.au> wrote: > > > > > Consider: > > > > if condition # no colon > > code > > else: > > code > > > > To actually "restart" parsing, you have to make a guess of some sort. > > Right. At least one of the papers on parsing I read over the last few > years (yeah, I really should try to find them again) argued that the > vast majority of syntax errors is either a missing token, a superfluous > token or a combination of the the two. So one strategy with good results > is to heuristically try to insert or delete single tokens and check > which results in the longest distance to the next error. > > Checking multiple possible fixes has its cost, especially since you have > to do that at every error. So you can argue that it is better for > productivity if you discover one error in 0.1 seconds than 10 errors in > 5 seconds.
Maybe; but what if you report 10 errors in 5 seconds, but 8 of them are spurious? You've reported two useful errors in a sea of noise. Even if it's the other way around (8 where you nailed it and correctly reported the error, 2 that are nonsense), is it actually helpful? Bear in mind that, if you can discover one syntax error in 0.1 seconds, you can do that check *the moment the user types a key* in the editor (which is more-or-less what happens with most syntax highlighting editors - some have a small delay to avoid being too noisy with error reporting, but same difference). Why report false errors when you can report errors one by one and know that they're true? > > > I grew up with C and Pascal compilers which would _happily_ produce many > > > complaints, usually accurate, and all manner of syntactic errors. They > > > didn't stop at the first syntax error. > > > > Yes, because they work with a much simpler grammar. > > I very much doubt that. Python doesn't have a particularly complicated > grammar, and C certainly doesn't have a particularly simple one. > > The argument that it's impossible in Python (unlike any other language), > because Python is oh so special doesn't hold water. > Never said it's because Python is special; there are a LOT of languages that are at least as complicated. Try giving multiple useful errors when there's a syntactic problem in SQL, for instance. But I do think that Pascal, especially, has a significantly simpler grammar than Python does. ChrisA -- https://mail.python.org/mailman/listinfo/python-list
