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Comment by Radim | Hacker News Reader

I know it's HN folklore to claim "Trivial! Would do over a weekend!", but please...

Doing a half-decent production spell checker is STILL a major feat. Same as "just crawling the web" (further down the discussion). Both require problem understanding and engineering you can't see and appreciate at a glance.

And no, looking up individual words in some predefined dictionary doesn't qualify as half-decent spell checking, especially for non-English languages. Spelling correction is another step.

    "Their coming too sea if its reel."

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That's not the point of the article. He's not talking about writing a state-of-the-art spelling-and-grammar checker.

> And no, looking up individual words in some predefined dictionary doesn't qualify as half-decent spell checking,

Well, but the author is talking about that problem! Even if you don't consider that real spell-checking, his point still stands. Let's define crappy-spell-checking as "looking up individual words in some predefined dictionary"; that problem used to be hard and now it's very easy, as in, you could write one in 15 minutes using Python.

Ok, fair point -- I blame the misleading title :)

I read the point of the article to compare "spell-checking then (80s) and now", whereas others read it more along the lines of "looking up static English words then and now". Your nickname sounds japanese, but I assume you're talking about English as well, with those 15 minutes.

Maybe it's not fair to cite the work of super heroes, but Peter Norvig wrote a spelling corrector in 21 lines of Python: http://norvig.com/spell-correct.html

It is fair, it is a first step in that direction :-)

That corrector has no context though, so it will not correct misspelled words that happen to come out as other words (incl. the "Their coming too sea if its reel.").

This is especially important on the web, where pretty much every conceivable word is "correct" (a name of a company or otherwise). False positives are costly, and context disambiguation critical. Let the fun begin.

You keep using this word "spelling". I don't think it means what you think it means.

This is GRAMMAR checking, or at least grammar-assisted spell checking.

Very few, if any, shipping mainstream spelling correctors do that.

People want their documents (or queries) free of spelling errors. That is their pain and that is the challenge.

The example sentence has misspelled words, hence is within the domain of spell checking. This type of misspelled words are called "homonyms", which are one very common spelling problem. The academic terminology is uninteresting to most users, however.

Or if you mean to posit that "spell checking really means looking up if a word exists in a static dictionary of English", then yes, that's easy and solved, no argument there.

> The example sentence has misspelled words, hence is within the domain of spell checking.

No, it doesn't . It is grammatically incorrect, but all the words are spelled correctly. You're definitely talking about a grammar checker, not a spelling checker.

I understand this is a mismatch in terminology.

In your view, "spelling check" is applied to individual words, to see if they appear in a fixed dictionary (see my other comment about difficulties with choosing this "correct" dictionary in reality, though). I can imagine this view is inviting for programmers, because it's easy to implement, but I doubt anyone else finds useful a definition that says there are no misspellings in "Their coming too sea if its reel."

In my view, "spell check" applies to utterances and roughly means "all words are spelled as per the norm of the language; I can send this document to my boss/customer and they won't laugh at my spelling." It is a more user-centric view, and more complex too, because it covers intent and norms, as opposed to the comforting lookup table for a few hand-picked strings. Modern spell checkers make heavy use of statistical analysis of large text corpora, to reasonably approximate context needed to model such intent.

Once we agree on the terminology, I believe we are in agreement, so let's not split hairs. The "correctly spelled" sentence under question comes from the Wikipedia article on spell checking, by the way.

I can imagine this view is inviting for programmers, because it's easy to implement, but I doubt anyone else finds useful a definition that says there are no misspellings in "Their coming too sea if its reel."

I realize this is just a debate over a definition, so it's not very meaningful, but the fact is, you're on the wrong side of the common definition here. I just tested, and every spell checker that I just checked (Chrome, Firefox, MS Word, TextMate, TextEdit - perhaps some of these rely on the same underlying engine, I'm not sure?) accepts that sentence as not having a spelling error, so clearly there's some use for such a definition.

The grammar checkers, on the other hand, don't like it, but by changing "their" to "they're", they all accept it, despite the fact that it's still garbage. So don't overestimate how good "modern" spell checkers are...though there may be techniques to do a better job, they're not in common use, at least in the most common spell-checking contexts (which, lets be honest, pretty much means MS Word).

There is no question whatever: the sentence contains misspelled words. "They're" is misspelled as "Their", "to" as "too", "see" as "sea", etc.

There is also no non-words. It happens that today's spelling checkers are generally just non-word detectors. This doesn't mean that anyone defines "misspelled" to mean "misspelled in such a way that the result is not a word at all".

And yes, a non-word detector is still very useful, and it's much much easier to make than something that also determines reliably when words are misspelled in ways that produce other words, so there's lots of software out there (perhaps essentially all of it) that contains only a non-word detector.

I think it's perfectly reasonable to define "spelling checker" to include mere non-word detectors. Or for that matter non-common-word detectors. (I expect most spelling checkers will reject "hight", and very sensibly because if someone types that they probably meant "high" or "height" or something -- but it's a perfectly good word, albeit a rare and archaic one.) But there's no way it's correct to say that "sea" isn't misspelled in that sentence merely because the mistake happens to have produced something that's an English word.

"""I think it's perfectly reasonable to define "spelling checker" to include mere non-word detectors. """

Sure it is (reasonable).

You just cannot go around acting as if such a definition is already widespread, established in tech discussions, and followed by spell checkers.

If you were a teacher marking a student's paper, you would label those as spelling errors, not a grammar errors. The reason is that a different spelling of the words would create the intended sentence. No grammatical variation will do that (reorders, conjugating differently, etc).

Really? Most teachers I had would put WW (wrong word) or WC (word choice) to imply that the word is incorrect, which is considered grammatical.

The sentence contains misspelled words. The errors in those words happen to make them collide with other existing words. That doesn't change the category of the error.

"""The sentence contains misspelled words."""

No, it contains correctly spelled words used in place of other desired words.

"I sea your eyes", "I she your eyes"

If you want to correct these kind of errors, you must now a lot about natural language. Also, the above are trivial cases. There are tons of edge cases and far more difficult distinctions. Here's an amusing one, that can lead to "Microsoft paperclip" like interactions:

"I gave him the new pink dress as a present" => "I gave her the new pink dress as a present"

No, idiotic spell-checker, I do mean him. My friend is a cross-dresser, shut up and let me type.

Such a spellchecker would also be useless for poetry. And if you find poetry obscure, so it doesn't really matter, then such a spellchecker would also be useless for irony. Suddenly, you lose all the hipsters from your potential users (except if they start using it ironically).

Anyway, no spell checker in widespread use attempts this --and it's probably a very hard nut to crack, and probably uncrackable in the general case.

> No, it contains correctly spelled words used in place of other desired words.

If you intend to write a word meaning "actually existing as a thing" and spell it "reel", it is monstrously unlikely that you genuinely thought a word meaning "a cylinder on which flexible materials can be wound" was a suitable substitute. If you did, that would be the use of a correctly spelled (but incorrectly selected) word in place of a desired word: a grammatical error, in other words. However, if you just pick the wrong letters to construct a phoneme, as is almost certainly the case here... yep, that's a spelling error.

To put it another way, imagine that the word "reel" didn't actually exist, and I make precisely the same error, substituting an 'e' for an 'a'. All of a sudden, by your argument, what was a grammatical error is now a spelling error. But the mistake I made hasn't changed, so that makes no sense.

> If you want to correct these kind of errors, you must now a lot about natural language. >... > Anyway, no spell checker in widespread use attempts this

So? The category of error doesn't change with how difficult it is to fix.

Hey, here's a chance to invent some new terminology!

I would say that Norvig's corrector is a first-order spelling corrector, since it works within the context of a single word.

A second-order corrector would take into account the word before or after it to choose the spelling that is more likely to make sense. ("Their coming" would suggest a correction to "They're coming")

Third-, fourth-, (and so on) order expands the distance of words considered.

"""("Their coming" would suggest a correction to "They're coming")'""

How about: "Her relatives would visit us for Christmas. Their coming filled us with dread!"

It's valid, but less common, and that's why I specifically chose the wording "suggest a correction" instead of "correct". Spell checkers are still no substitute for actual thought.

No, it's spell-checking. Use of the word "reel" in this sentence, for instance, is definitely a spelling error. There's no grammatically valid form of the word "real" spelled with two 'e's. The fact that "reel" happens to be a valid word doesn't mean that its presence in the sentence is due to a grammatical error - it's just an accidental collision.

That no spell checker might be able to catch this specific class of error doesn't change the type of error it is.

Incidentally, the linked article by Peter Norvig also mentions that adding context is the best way to improve spelling correction. If you think this claim is so controversial, explain yourself, don't just downvote please.

That'd be a grammar checker, that's a whole 'nother beast. That should spell check just fine.

spell checking for languages that sport a high rate of agglutination where you can't (feasibly) enumerate every possible form of a stem is still a major feat. languages like turkish, finnish and hungarian are prime examples of this.

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