A 220b spreadsheet app in HTML/JS
xem.github.io
xem.github.io
I'm xem, author of this mini app, but standing on the shoulders of giants:
it's inspired by http://aem1k.com/sheet/
which was inspired by http://jsfiddle.net/ondras/hYfN3/
Cheers to all the JS codegolf team who teached me this noble art and continue to learn new tricks everyday with me!
You can find a list of all our mini apps here: https://gist.github.com/xem/206db44adbdd09bac424
Cheers
To be fair, it only adds an extra 18 chars, taking it up to 238-byte in size.
EDIT Here it is once you add the extra property:
(o=b=>{for(j in a)for(i in a)y=a[i]+-~j,b?document.write([["<p>"][i]]+"<input onfocus=value=[o[id]] onblur=o[id]=value;o() id="+y+" placeholder="+y+">"):eval(y+(".value"+o[y]).replace(/[A-Z]\d/g," +$&.value"))})(a="ABCD")Tongue in cheek aside, very creative code. Thank you for sharing
<script>(o=b=>{for(j in a)for(i in a)y=a[i]+-~j,b?document.write([["<p>"][i]]+`<input onfocus=value=[o[id]] onblur=o[id]=value;o() id=${y}>`):eval(y+(".value"+o[y]).replace(/[A-Z]\d/g," +$&.value"))})(a="ABCD")</script> (o=b=>{for(j in a)for(i in a)y=a[i]+j,b?document.write(`<${i*j?'input':'p'} onfocus=value=[o[id]] onblur=o[id]=value;o() id=${y}>`):eval(y+(".value"+o[y]).replace(/[A-Z]\d/g," +$&.value"))})(a="_ABCD")Can somebody explain to me how: "a[i]+-~j" is the same as "a[i]+(j+1)" ?
-(~j) = Twos complement of the ones complement of j
Twos complement = ones complement + 1
So twos complement of (ones complement of j) = ones complement of (ones complement of j) + 1 = j + 1
The cool thing is you could code some extra features or an entire SPA inside the spreadsheet. Better than XL.
A1: 0
A2: =A1+5
A1: =A2*3
I guess you would have to sanitize when you save and/or load the spreadsheet
Sanitizing? No chance. Either you have a dedicated expression parser, or you run it directly throgh eval. There is no reliable middle ground. Decades of security failures of so-called "sanitizers" show this pretty clearly.
(Even if you manage to create a perfect sanitizer today, wait a few months, new features are added to the browser, and new loopholes will appear out of nothing.)
But that may be missing the point, because if you want more code quality, more safety and more features, of course you need more code. This demo illustrates the other way around: If you allow for dirty hacks, you can get away with a surprisingly small amount of code.
That's exactly what I meant by "dedicated expression parser".
(Not sure why you name it "matcher", though. Please be aware that a regex-based matcher will almost certainly fail for that task. You usually want a grammar, i.e. parser, which is more powerful, and shorter, and easier to read and to verify.)
EDIT: To those who downvoted my clarification, do you care to elaborate?
you are probably making too much sense.
If you relax the rules, as the gp said, you can get away with something like a regex to do the job. While regex's are bad at context free grammars [0], if you forgo balancing brackets etc. a regex will do just fine.
All that said, with the crazy things JS lets you do [1] a recogniser for a relaxed language is likely to still let potentially dangerous code though.
[0] Yes, with most regex engines you can parse CFGs, but it's not nice, and at that point you _do_ want a grammar based parser
Please note that the term "recogniser" is very fuzzy, it could mean a regex matcher, a parser or even a turing-complete thing. Not very helpful for this discussion.
> a parser, which outputs a data structure
Please note that a parser is not required to output a data structure. In classic computer science, the parser of a context-free grammar usually has a minimal (boolean) output: it just either accepts or rejects the input.
If your "recognizer" is too weak (e.g. regexes), you risk not properly checking the language (see below).
If your "recognizer" is too powerful (e.g. turing complete), you risk tons of loopholes which are hard to find and hard to analyze. You probably won't be able to prove the security, and even if you do, it will probably be hard work, and even harder for others to follow and to verify.
But if your "recognizer" is a parser, you have a good chance to succeed in a safe way with minimal effort. Proving security is as simple as comparing your grammar with the ECMAscript standard.
> you can get away with something like a regex to do the job [...] with the crazy things JS lets you do a recogniser for a relaxed language is likely to still let potentially dangerous code though
That's exactly my point: Sure, you can try to build a protection wall based on regexes, but there's no reason to do that. Use a proper parser right away and don't waste your time with repeating well-known anti-patterns.
All of the literature I remember from my uni days on formal grammers had a recogniser defined as something that accepts/rejects, and a parser as something that builds a data structure.
It's difficult to retrospectively find the literature, because outside of formal grammars recogniser _is_ used more loosely. But a few Wikipedia articles [1] [2] [3] and their referenced literature [4] [5] do agree with me.
> A recognizer is an algorithm which takes as input a string and > either accepts or rejects it depending on whether or not the string > is a sentence of the grammar. A parser is a recognizer which also > outputs the set of all legal derivation trees for the string.
[1] https://en.wikipedia.org/wiki/Parsing#Computer_languages
[2] https://en.wikipedia.org/wiki/Earley_parser#Earley_recognise...
[3] https://en.wikipedia.org/wiki/CYK_algorithm#Generating_a_par...
[4] http://reports-archive.adm.cs.cmu.edu/anon/anon/usr/ftp/scan...
While there is no safe middle ground, using eval directly is the worst case; it's not a case where those extremes reliable and there is greater danger in between.
That being said, rejecting everything that fails an expression parser is a form of sanitization.
If your whitelist allows a wide range of constructs, it isn’t much easier to check that an input is in the allowed set than to write an evaluator that is limited to that set, so it may not be much of an advantage to have a more powerful ”eval” lying around.
Pretty fun, though
Well done!
Thanks!
ah, if only we could all code just what we needed, instead of over-engineering solutions to problems we wished we had
With modern languages and tooling, you can have the benefits of most of these things at little-to-no additional cost. If any of these require something complicated and "over-engineered", I'd instead describe it as "bad engineering".
Rule one is making code that works correctly and quickly, in a short about of time. This is 100% of the job.
If you think that "maintainability" and "readability" and "popular" libraries, and "code reuse" and "good variable names" and code that "smells good" to you, help someone do that, then great: That's an argument we can have just by pointing to anyone who gets rule one without those things.
However.
There's another kind of person - and there's a lot of them - who thinks those things are important by themselves, and that putting those things ahead of what I think are rule one is ever acceptable.
The number of times I've heard some "experienced" programmer say with all earnestness that we should ask for another 1/4 million dollars of tin so that he can use his "clean" (but slow) algorithm makes me wary of anyone who uses those words you just used in seriousness.
That's the person the parent comment is mocking.
I think you totally understood my humor. Thanks!
I saw a good blog in 2011 about how it is a waste of time to overbuild things since mostly you are only ever going to use that code for the specific purpose you are writing it, and you'll likely never need to generalize and you'll probably chuck it out anyway and start from scratch.
Obviously there are a bunch of caveats to that and it's not always true that's the case but I think it's a very useful counterpoint to the profession's current best-practice obsession. If you keep it in mind, alongside all the best practices, and you make a choice about approach in any given situation based on appropriateness, rather than just robotically applying best practices or giving into that common Engineer's temptation to overbuild, this counterpoint can help you build quickly just what's needed, which is effective, exactly like you said.
I don't think those caveats are obvious to a junior (or otherwise inexperienced) developer. Maybe some of them are obvious, but I don't think anyone runs into these enough daily that programming by dogma actually helps.
And yet I do see value if there are rules! Why should we think about having "good variable names" or not if most of the time "good variable names" don't cause much harm, and most of the time not having them does?
It's just that I don't think this is a real problem; I don't believe anyone actually makes that choice.
I think if something doesn't have "good variable names" (as an example), then it's possible someone was programming who couldn't think of good ones (to which the rule wouldn't help anyway), and it's possible that these are good variable names, and that it's our opinion that is wrong (perhaps because we don't yet understand what we're looking at). NB) I'm not saying both are equally likely.
To put it another way, how can one recommend programming by brute force, "as long as you've got "readability" and "popular" libraries, and "code reuse" and "good variable names" and so on... What can we possibly add to that list that will be even a good substitute for a few decades of experience successfully delivering software?
I mean, security and maintainability is important, but the most secure and maintainable code is always the code that didn't get written in the first place, which makes not writing unnecessary code a no.1. way of making the result not suck.
Why climb Everest? Why play a video game on the hardest setting? Why learn to write Hello World in the top 100 programming languages?
I can't say I wrote a spreadsheet in 220b. They can.
Maybe the question is, "Why not?" It is Hacker News, after all.