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> The motivation for many splitting out a prime-testing function is that primality testing is hard to do efficiently Yes. Also that there are many ways to do

by jonahx 7y ago

> The motivation for many splitting out a prime-testing function is that primality testing is hard to do efficiently Yes. Also that there are many ways to do it, the details of which you don't necessarily care about. > Nothing is being abstracted here It absolutely is. To abstract is to ignore differences. Here you are abstracting over the methods used to do primality testing. If you are using "1&p:" in J to test if something is prime, you are saying something like: "I don't care exactly how it's done, just that it uses one of the reasonably fast and correct algorithms available." > nothing is gained by indirection: Does this is-prime routine even deserve a name? I am so baffled by these claims that I wonder if I'm missing your point. My reaction is: A tremendous amount is gained by this abstraction. It is exactly the abstraction you want most of the time. And yes, it deserves a name, because "Is it prime?" is how everyone thinks about it and talks about. It links up with the whole history and culture of mathematics.

geocar 7y ago
> I am so baffled by these claims that I wonder if I'm missing your point. My reaction is: A tremendous amount is gained by this abstraction. addOne =. 1+[ isPrime =. 1&p: I do not think these functions are useful enough abstractions to be given a separate functions.
- jonahx 7y ago
  > addOne =. 1+[ The J authors did (correctly imo) think that it was. It's called ">:". > isPrime =. 1&p: In this case it does not, although I'd argue it's not so much about "isPrime" not being a useful concept worth naming on its own, as that J is a dense language working with a limited character set and there are a bunch of related concepts around "primeness" that need to packed into the "p:" verb -- accomplished in this case allowing the left argument to access a bunch of different verbs worth naming. Said another way, "1&p:" just happens to be the way J names this concept, for reasons of economy. For the prime case in particular, it will be a named function in most math libraries that deal with such things, or languages where such math is central to the domain: https://reference.wolfram.com/language/ref/PrimeQ.html https://reference.wolfram.com/language/ref/PrimeQ.html I am still unclear what your claim is: that such functions are always an example of "too much abstraction"? If so, I don't think that claim is tenable.
  - geocar 7y ago
    > The J authors did think that it was. It's called ">:". So did CL. I still disagree though: >:/ is different than (1+])/. 1++:i. is the same number of characters as >:+:i. I feel like there are many more valuable functions more deserving than this one. > I am still unclear what your claim is: that such functions are always an example of "too much abstraction"? If so, I don't think that claim is tenable. Sorry it's so difficult to figure out; You're not asking really constructive questions, so maybe one of my other replies will help. I'm not saying anything is always one way or another because I think the only absolute is that it always depends!

by jonahx 7y ago

geocar 7y ago

> I am so baffled by these claims that I wonder if I'm missing your point. My reaction is: A tremendous amount is gained by this abstraction. addOne =. 1+[ isPrime =. 1&p: I do not think these functions are useful enough abstractions to be given a separate functions.

jonahx 7y ago
> addOne =. 1+[ The J authors did (correctly imo) think that it was. It's called ">:". > isPrime =. 1&p: In this case it does not, although I'd argue it's not so much about "isPrime" not being a useful concept worth naming on its own, as that J is a dense language working with a limited character set and there are a bunch of related concepts around "primeness" that need to packed into the "p:" verb -- accomplished in this case allowing the left argument to access a bunch of different verbs worth naming. Said another way, "1&p:" just happens to be the way J names this concept, for reasons of economy. For the prime case in particular, it will be a named function in most math libraries that deal with such things, or languages where such math is central to the domain: https://reference.wolfram.com/language/ref/PrimeQ.html https://reference.wolfram.com/language/ref/PrimeQ.html I am still unclear what your claim is: that such functions are always an example of "too much abstraction"? If so, I don't think that claim is tenable.
- geocar 7y ago
  > The J authors did think that it was. It's called ">:". So did CL. I still disagree though: >:/ is different than (1+])/. 1++:i. is the same number of characters as >:+:i. I feel like there are many more valuable functions more deserving than this one. > I am still unclear what your claim is: that such functions are always an example of "too much abstraction"? If so, I don't think that claim is tenable. Sorry it's so difficult to figure out; You're not asking really constructive questions, so maybe one of my other replies will help. I'm not saying anything is always one way or another because I think the only absolute is that it always depends!