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There are now people closing computer science questions as off-topic.

We were explicitly promised that this wouldn't happen when the CS site was created.

Could we stop that, please?

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    $\begingroup$ I think on your second link, you probably wanted to link to this instead. Either way, it is not so clear that the question would have been on topic if what you call the "CS ghetto" would not exist. $\endgroup$ – Michael Greinecker Apr 12 '12 at 12:19
  • $\begingroup$ @Michael: Why would it not be on topic? It asks for clarification of some notation used in a presentation of a mathematical theory the OP is trying to learn. Do you think that questions about notation should in general be unwanted here? $\endgroup$ – Henning Makholm Apr 12 '12 at 12:23
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    $\begingroup$ To me it is not clear whether the question of OP wasn't simply about MinML, which was the only context given. $\endgroup$ – Michael Greinecker Apr 12 '12 at 12:33
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    $\begingroup$ @Henning, correct me if I'm wrong but this is about a syntax of a specific programming language (or am I wrong?) which I cannot for the life of me see as on topic, even if there were no cs.SE sites except SO itself. $\endgroup$ – Asaf Karagila Apr 12 '12 at 12:33
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    $\begingroup$ I very much agree with Michael, there is no context to the question except a screenshot titled "Abstract syntax of MinML", if you wish to edit the question and add some context that will make it clear that this question is on-topic in a mathematics Q&A site then I'd be glad to vote to re-open. $\endgroup$ – Asaf Karagila Apr 12 '12 at 12:35
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    $\begingroup$ @Michael: How is that different from asking what $d/dx$ means and giving a specific calculus textbook as the only context? MinML, it should be quite clear, is not something anyone studies for its own sake; it is merely a toy example for presenting some general ideas in a mutually consistent form. $\endgroup$ – Henning Makholm Apr 12 '12 at 13:03
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    $\begingroup$ @Henning: The difference is that one can be pretty sure that the notation in a calculus textbook refers to mathematical notation and is not the ideosycraticism of a programming language. If you see an example in a calculus textbook about the growth rate of a population of Pentalagus furnessi, M.SE wouldn't be the right place to ask what Pentalagus furnessi means. $\endgroup$ – Michael Greinecker Apr 12 '12 at 13:17
  • $\begingroup$ I didn't vote to close, but I guess I started the closure ball rolling, so I ought to comment here. I don't know what MinML is, but from context it appeared to be some computing language. I don't want to see questions here on what this or that symbol means in Fortran or Cobol (regardless of the existence of more suitable sites), and I took this to be that kind of question. Was I wrong? $\endgroup$ – Gerry Myerson Apr 12 '12 at 13:20
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    $\begingroup$ @Michael: I'm equally pretty sure that the notation in this question refers to standard notation in the mathematical theory of types in programming language and is not an idiosyncrasy of the example language being used (except for the horrible typography in the slides, writing -> instead of $\to$). $\endgroup$ – Henning Makholm Apr 12 '12 at 13:33
  • $\begingroup$ @Gerry: I don't have any prior knowledge of "MinML", but it is extremely clear even from the limited information in the questions that is not a programming language anyone uses to write programs, but a toy model of an idealized programming language that is being used to teach students how to reason mathematically about programming languages in general. Is your contention that simply because the mathematical theory the question is about can be applied to Fortran, questions about that mathematical theory should be asked on SO instead of here? $\endgroup$ – Henning Makholm Apr 12 '12 at 13:36
  • $\begingroup$ Moreover, it is very likely that "MinML" exists only in the particular slide side the OP is quoting from. That kind of toy examples are throw-away constructions. $\endgroup$ – Henning Makholm Apr 12 '12 at 13:43
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    $\begingroup$ @Henning: Googling "MinML" shows that it does actually exist outside some example slide. See for example here. The horrible typography was probably not horrible typography but correct code. People use Scheme mostly to illustrate ideas, but questions about Scheme commands would certainly be off-topic, and it is unclear whether OPs confusion wasn't on that level. $\endgroup$ – Michael Greinecker Apr 12 '12 at 15:25
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    $\begingroup$ @HenningMakholm: I take it there is no tradition of MinML. A perfectly acceptable version of the question would be this: "I read this |paper/book| on |mathematical topic in CS| and saw this symbol I'm not familiar. It looks like this: |Screenshot|." I don't think that question would have been closed. In a question about notation, providing context is especially important. There are certainly lots of uses of the arrow-symbol in mathematics. $\endgroup$ – Michael Greinecker Apr 12 '12 at 23:23
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    $\begingroup$ @MichaelGreinecker: There is a tradition of teaching type systems, and part of that tradition involves defining toy languages to show off one's concepts. Also, I fully agree that the question was badly asked, but here we are discussing whether it is on topic for MSE or not. What is on topic or not is (or should be) orthogonal to how well one particular question about it is presented. $\endgroup$ – Henning Makholm Apr 12 '12 at 23:29
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    $\begingroup$ @HenningMakholm: In that case I presume the essential problem was not one of policy guidelines. To the untrained eye, the question looks like an off-topic coding question and that was why it was closed. I just gave my vote for reopening. It seems there is no actual danger that people consider type theory unfit for M.SE. Peace. $\endgroup$ – Michael Greinecker Apr 12 '12 at 23:33
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EDIT: The question has been reopened. I have cast my vote to close. If you think the question is off-topic...

While you raise a possibly valid concern, the example you choose is not right.

IMO, the MinML notation question is not on-topic on a Mathematics site.

I am thinking of it this way: Can a mathematics professor who has no knowledge of MinML answer this question without reading up about MinML? No.

The fact that this is the same notation used in Mathematics is irrelevant: you cannot possibly know that without understanding what MinML is about.

Given that MinML is not mainstream/a language which you expect a reasonable proportion of mathematicians to be familiar with(as you claim in a comment)/use, questions about MinML are very likely off-topic.

There are computer science questions which are on-topic and welcome here. That does not mean all of them are on-topic.

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    $\begingroup$ I agree with this answer, except that even if the question was "What does bool stand for in C?" it would still be off-topic. The fact that the language is obscure has nothing to do with the fact that questions about notation related to a computer programming language (in the broad sense of the term) is certainly off topic on math.SE. $\endgroup$ – Asaf Karagila Apr 12 '12 at 20:51
  • $\begingroup$ @AsafKaragila: I had mathematica type math-oriented languages in mind when I wrote that. $\endgroup$ – Aryabhata Apr 12 '12 at 22:20
  • $\begingroup$ Well, now with the new mathematica.SE site running wild, I see no reason why Mathematica would be on-topic. I guess that you might be right and GAP/MATLAB/etc. would be on-topic here after all. $\endgroup$ – Asaf Karagila Apr 12 '12 at 22:22
  • $\begingroup$ @AsafKaragila: Yeah, not just mathematica :-) $\endgroup$ – Aryabhata Apr 12 '12 at 22:27
  • $\begingroup$ I am not a mathematics professor, but I have no particular knowledge of MinML, and I can answer questions about it, under the assumption that it is fairly conventional toy language resembling the ML family. Mathematicians who work in this area can reasonably be expected to be able to infer the details of such teaching examples, just like people can be expected to deal with minor notation variants and per-author idiosyncracies in every other mathematical area. $\endgroup$ – Henning Makholm Apr 12 '12 at 22:59
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    $\begingroup$ @Asaf, I agree that "what does bool stand for in C" would be off-topic, but this question is nothing like that. C is a particular language used in the real world -- C code is written on computers, in stark contrast to the toy language in this post, which is written on whiteboards. $\endgroup$ – Henning Makholm Apr 12 '12 at 23:01
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    $\begingroup$ @Henning: Much like myself and Michael are arguing - that would have to require some context. I can assure you that if someone had posted a question "What does $\to$ mean?" it would generate a lot of negative buzz, probably closed and maybe get some +60 votes answer listing all the reasonable usage of $\to$ in mathematics. In the case you brought up, the minimal (and very vague!) context given was already creating a negative buzz and the question was closed without generating a +60 votes answer. $\endgroup$ – Asaf Karagila Apr 12 '12 at 23:28
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    $\begingroup$ @Asaf: There is sufficient context for one familiar with the area to see what it is about. Are you really proposing that the definition of which areas of mathematics are welcome on MSE should depend on whether someone has posted an ill-written question about them? Or are you arguing that MSE should welcome only areas of mathematics in which it is impossible to ask a question in a vague uninformative way? $\endgroup$ – Henning Makholm Apr 12 '12 at 23:34
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    $\begingroup$ @Henning: Right now I'm suggesting a good night sleep. This is at least what I intend to try. Arguing online can be tiresome and a good rest can do wonders! :-) $\endgroup$ – Asaf Karagila Apr 12 '12 at 23:36
  • $\begingroup$ @HenningMakholm: What if the question was about the meaning of ::=? Would that be on-topic? What about ; (which is probably a statement delimiter)? You can guess whatever answer you want, but without some knowledge of MinML, you don't have an objective answer. All you have is an opinion/guess. If the question was, in Type Theory what does blah notation mean, then I agree it would be on-topic. The fact that the notation in MinML is borrowed from Mathematics, is irrelevant and does not make it on-topic. The context does matter. $\endgroup$ – Aryabhata Apr 13 '12 at 0:10
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    $\begingroup$ @Aryabhata: You are persisting in refusing to see what is plainly there, namely that the abstract syntax being defined is not for any real-world example but for a toy example designed to teach type theory as a general subject. The reason this is plain is that a language with only int, bool and function types would be absolutely, impossibly, cumbersome to write any real program. There is no possible world in which the types presented on that slide could be used to write programs on real computers that solve real problems. Its only possible use is to teach the mathematical theory of types. $\endgroup$ – Henning Makholm Apr 13 '12 at 21:02
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    $\begingroup$ @Aryabhata: I agree with Henning. I have no working knowledge of any functional programming language whatsoever but I can see that the slide is not about the syntax of a programming language but rather the type system of a programming language. $\endgroup$ – Zhen Lin Apr 13 '12 at 21:25
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    $\begingroup$ @ZhenLin: No. I am not proposing that OP answer their own question, just that they provide more context: is it the syntax of the language they have a question about (which seems clear from what is written)? Or something else (which you seem to be reading the original question as)? Again, you are reading more than what was intended! $\endgroup$ – Aryabhata Apr 13 '12 at 21:36
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    $\begingroup$ I voted to re-open not because I have strong opinions on whether that particular question is on-topic or not, but rather because the "off-topic" reason apparently sends a wrong signal, as the present thread indicates. To be honest, I find it an abysmally bad question (it's just a screen shot + "what's this?", after all) and I could live with either one of "too localized", "not constructive" or "not a real question", but the comments clearly indicated that it was the topic that led to closure and I disagree with that. $\endgroup$ – t.b. Apr 13 '12 at 23:25
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    $\begingroup$ I'm upvoting the answerer and the OP because both raise valid points... I like meta questions like this because I can't decide who I think is right. $\endgroup$ – Camilo Martin Apr 14 '12 at 5:28

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