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2 points by zck 18 days ago | link | parent | on: Running arc from outside the arc2.3 dir?

What OS are you on? If you're on Linux or MacOS, you can use `pushd` and `popd`.

On bash, I have some aliases set up. they will move you to the right directory, run arc or anarki, then when it exits, move you back to the original folder.

alias arc="pushd ~/programs/arc/arc3.2/; rlwrap racket -f as.scm; popd" alias anarki="pushd ~/programs/arc/anarki/; ./arc.sh; popd"

I normally use fish shell, but functions there are simple enough to make based on the bash aliases.

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2 points by markjreed 18 days ago | link

Getting back after arc is not the problem; even if I didn't have cd history set up a simple `cd -` would handle that.

Simple problem: I have a file containing a program written in Arc. I want to run it from the shell. How do I do that? I can fire up arc and `(load)` the file, but then the file needs to be in the arc2.3 dir or else I have to load it by absolute path, even if I was just in the same directory it's in.

For now I've just switched to using Anarki; I can run its `arc.sh` start script from anywhere in the filesystem and feed it a locally-relative pathname and it will run. Although it does seem to take quite a lot longer to start up than arc.

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3 points by zck 114 days ago | link | parent | on: Please test: expanding user directories

Ah, interesting. That's a good point that it's Unix/MacOS-specific. My hope was that it should make Arc interpret paths the same way the default shell on the system does. On Linux, ~/ is the home directory of the current user, so it makes sense that Anarki would work that way on Linux. But Windows doesn't work that way, so it makes sense Anarki wouldn't either.

I don't know of any similar path tricks on Windows, But, if this change hasn't broken anything on Windows, I would be satisfied with that. Can you verify it still works to open an existing file? Are there any other special ways to refer to files or directories on Windows?

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2 points by rocketnia 107 days ago | link

"On Linux, ~/ is the home directory of the current user, so it makes sense that Anarki would work that way on Linux. But Windows doesn't work that way, so it makes sense Anarki wouldn't either."

Yeah, I don't know much about what a Windows user would expect ~ to do. I would say `expand-user-path` leaving ~ alone on Windows is probably as good a behavior as any. It coincides with Command Prompt, where ~ just refers to a file or folder named "~". In PowerShell, ~ seems to be expanded to C:\Users\[username]\ somehow, so there's potentially an alternative design there.

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"I don't know of any similar path tricks on Windows, But, if this change hasn't broken anything on Windows, I would be satisfied with that. Can you verify it still works to open an existing file?"

On Windows 10 64-bit with Racket 8.1, I've at least run the tests.arc unit tests, the unit-test.arc/tests.arc unit tests, and build-web-help.arc, and they seem to work.

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"Are there any other special ways to refer to files or directories on Windows?"

Racket deals with a lot more Windows path features than I've ever learned about or encountered, and there's some gritty documentation of that here: https://docs.racket-lang.org/reference/windowspaths.html

I hardly know where to begin learning about and testing those features, and the documentation makes it look like Racket has explored hat rabbit hole pretty thoroughly already, so I'm inclined to suggest we just piggyback on Racket's work here.

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I just ran the unit-test.arc unit tests on both Arc3.1 and Anarki master, and they ran in virtually the same time. Arc3.1 took 49 seconds, and Anarki took 51 seconds.

Certainly would be worth trying to optimize. I'm sure there are a lot of improvements to be had, both in unit-test.arc and Anarki.

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Hrm. The tests definitely were faster. They weren't as fast as I'd wanted, but certainly not this slow. It just took three minutes for me to load that file. It's slightly complicated by that file loading _and_ running the tests, but again, it wasn't that slow before. For reference, I'm on Ubuntu running Racket 8.1.

One thing that definitely has changed is that now, Anarki requires Racket >=7.7. I just had to update my Racket from 7.2, which worked the last time I ran Anarki, Perhaps this is related?

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2 points by akkartik 143 days ago | link

I also see some failures in unit-test.arc:

    (require 'lib/unit-test.arc/unit-test.arc)
    (load "lib/unit-test.arc/tests.arc")
    (test-and-error-on-failure)

    unit-test-tests.suite-creation.add-tests-to-suite.tests-are-wrapped-to-create-test-result-template failed: (isa result (quote table)) should be nil but instead was nil
    unit-test-tests.remove-thing.remove-nothing-from-single failed: (remove-thing (quote (not-found)) single-suite) should be (obj (single #s(ar-tagged tem (suite #hash((full-suite-name . suite-with-no-full-name) (nested-suites . #hash()) (suite-name . suite-with-no-name) (tests . #hash((nested . #s(ar-tagged tem (test #hash((suite-name . test-with-no-suite-name) (test-fn . #<procedure: g5264>) (test-name . test-with-no-name)) #hash())))))) #hash())))) but instead was (obj (single #s(ar-tagged tem (suite #hash((full-suite-name . suite-with-no-full-name) (nested-suites . #hash()) (suite-name . suite-with-no-name) (tests . #hash((nested . #s(ar-tagged tem (test #hash((suite-name . test-with-no-suite-name) (test-fn . #<procedure: g5264>) (test-name . test-with-no-name)) #hash())))))) #hash()))))
    unit-test-tests.remove-thing.remove-nested-test failed: (remove-thing (quote (single double one)) two-nested-tests) should be (obj (single #s(ar-tagged tem (suite #hash((full-suite-name . suite-with-no-full-name) (nested-suites . #hash((double . #s(ar-tagged tem (suite #hash((full-suite-name . suite-with-no-full-name) (nested-suites . #hash()) (suite-name . suite-with-no-name) (tests . #hash((two . #s(ar-tagged tem (test #hash((suite-name . test-with-no-suite-name) (test-fn . #<procedure: g5264>) (test-name . test-with-no-name)) #hash())))))) #hash()))))) (suite-name . suite-with-no-name) (tests . #hash())) #hash())))) but instead was (obj (single #s(ar-tagged tem (suite #hash((full-suite-name . suite-with-no-full-name) (nested-suites . #hash((double . #s(ar-tagged tem (suite #hash((full-suite-name . suite-with-no-full-name) (nested-suites . #hash()) (suite-name . suite-with-no-name) (tests . #hash((two . #s(ar-tagged tem (test #hash((suite-name . test-with-no-suite-name) (test-fn . #<procedure: g5264>) (test-name . test-with-no-name)) #hash())))))) #hash()))))) (suite-name . suite-with-no-name) (tests . #hash())) #hash()))))
    unit-test-tests.remove-thing.remove-one-of-two-suites failed: (remove-thing (quote (first)) two-suites) should be (obj (second #s(ar-tagged tem (suite #hash((full-suite-name . suite-with-no-full-name) (nested-suites . #hash()) (suite-name . suite-with-no-name) (tests . #hash((nested . #s(ar-tagged tem (test #hash((suite-name . test-with-no-suite-name) (test-fn . #<procedure: g5264>) (test-name . test-with-no-name)) #hash())))))) #hash())))) but instead was (obj (second #s(ar-tagged tem (suite #hash((full-suite-name . suite-with-no-full-name) (nested-suites . #hash()) (suite-name . suite-with-no-name) (tests . #hash((nested . #s(ar-tagged tem (test #hash((suite-name . test-with-no-suite-name) (test-fn . #<procedure: g5264>) (test-name . test-with-no-name)) #hash())))))) #hash()))))

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3 points by zck 142 days ago | link

Updated unit-test.arc to the latest. PR at https://github.com/arclanguage/anarki/pull/205

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2 points by zck 142 days ago | link

Hrm, this should have been failing for a while. It comes down to functions never being able to be `iso` to each other.

  arc> (iso (fn ()) (fn ()))
  'nil
I suspect this might've changed in the new Racket? I hope this hasn't snuck through for so long.

Anyway, working on a fix now.

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3 points by rocketnia 142 days ago | link

At one point, years ago, I relied on every lambda returning a newly allocated object. I think I brought it up as a bug in Rainbow that the [] expressions in my Arc code were generating the same lambda-lifted result instead of creating unique objects each time.

But I think this was never something I could rely on in the original, Racket-based Arc either. The Racket docs don't specify whether a lambda expression returns a new object or reuses an existing one, and in fact they explicitly allow for the possibility of reusing one:

"Similarly, evaluation of a lambda form typically generates a new procedure object, but it may re-use a procedure object previously generated by the same source lambda form."

That sentence has been in the reference since the earliest versions I can find online:

The latest docs, currently for 8.1 (2021): https://docs.racket-lang.org/reference/Equality.html#%28part...

5.0 (2010): https://download.racket-lang.org/docs/5.0/html/reference/eva...

4.0.0.1 (2008): https://web.archive.org/web/20080620030058/http://docs.plt-s...

3.99.0.13 (2008): https://web.archive.org/web/20080229164003/http://docs.plt-s...

I'm not sure if the bug you're referring to had to do with making the same mistake I was making back then, or if you're talking about making the opposite assumption (expecting two procedures to be equal), but it's probably best not to expect stability either way.

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2 points by zck 141 days ago | link

I was doing a deep-`iso` comparison I called `same`, because in Arc, hash tables are not the same. In Arc3.1:

  arc> (iso (obj) (obj))
  nil
  arc> (iso (obj 1 2) (obj 1 2))
  nil
So I made a function that iterated over the key/value pairs and compared them. In some unit tests, I used that on a hash table that contained functions. Yesterday, I refactored the unit tests to instead make sure the keys were right.

Interestingly, it seems that Anarki can compare hash tables:

  arc> (iso (obj) (obj))
  't
  
  arc> (iso (obj 1 2) (obj 1 2))
  't
Anyway, this should fix the unit test tests in the Anarki repo.

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2 points by zck 142 days ago | link

Oh jeez, let me take a look.

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2 points by akkartik 142 days ago | link

Not on you. I know we forked it as well a while ago.

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1 point by krapp 142 days ago | link

>should be nil but instead was nil

I'm sorry, what?

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1 point by zck 142 days ago | link

It's printing out the two values it's comparing. Not sure yet why they're not the same.

It makes more sense when you see an error message like "should be 3 but instead was 2".

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3 points by zck 185 days ago | link | parent | on: Arc Installation

The "racket -f as.scm" is supposed to be done in your terminal, you're right! DrRacket is a different thing that is very cool, but not the tool to run Arc with.

When you type it in your terminal, what does it say? If it says something like "racket not found", try downloading the racket installer from https://download.racket-lang.org/.

If it installs correctly, you should be able to type "racket" (without quotes) in your terminal, and get a message "Welcome to Racket 8.0". To quit, press Ctrl-D, or type (exit) with the parentheses, then hit enter.

If that works, you should be able to run "racket -f as.scm".

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3 points by svk 185 days ago | link

Thank you so much, zck :) I've used a combination of your helpful suggestions, stack overflow, and cd command to get to the right folder, and now it works. I got the arc command prompt (arc>) in my terminal now. I will take my time to explore the tutorial on Arc. I feel good that this community is really helpful. Thanks everyone!

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Super interesting! I like how you can zoom into the system, almost like using a microscope to see how code works.

One thing that isn't quite clear from your examples here (and maybe that wasn't the point, but I am wondering): why have a different stack when a function is called? Your examples would work fine if they used the same stack. That is, if functions used the same stack, `1+` could be defined as `1 +`.

Perhaps it would be more clear if an example used two variables, or used the same variable twice.

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3 points by akkartik 378 days ago | link

That's a great point. As I've built this, the keystone example in my mind has been the `square` function:

    x square = x x *
So it's really funny that I haven't added it yet. Now added.

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2 points by zck 378 days ago | link

Nice!

Is it that you're trying to reduce stack juggling? That's hard to understand from simple examples (that you need to have to grok the syntax). Maybe compare something like finding the hypotenuse of a right triangle given the two other sides. Without naming arguments, you'd have to do something like:

  hypot = dup * swap dup * + sqrt
But with named arguments:

  hypot x y = x x * y y * + sqrt
That seems a little easier to read, but even the original isn't so complicated. Is there an example that makes it more obvious why it's better? Even your `square` example is more tokens than with stack juggling (without arguments, `square = dup *` is just four tokens, compared to six with named arguments). I'd say the with-arguments one is easier to read, but I've far less familiar with stack-based postfix programming.

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2 points by akkartik 378 days ago | link

Yeah, some other polynomial might be a better example. The Pythagorean formula has a clean separation when it comes to which args each term uses. How about the roots of a quadratic equation when you start out with a, b and c on the stack?

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2 points by zck 377 days ago | link

Yes, that is definitely simpler, although the formula is more esoteric. At least, for me, it triggers the "I was taught this in school and haven't used it since" filter.

Maybe something like:

  total-price cost-per-item number-of-items shipping-cost-per-item rush-cost = cost-per-item number-of-items * shipping-cost-per-item number-of-items * + rush-cost +
This doesn't seem super great; it could be refactored to use each thing once, but it's late and I can't think of any better example.

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2 points by akkartik 377 days ago | link

You're right that in general any such example can be refactored to reduce stack operations. That's even a fun game for many Forth programmers to play. (We lispers have our own equivalents.) But it usually makes the code less comprehensible, in my experience.

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2 points by zck 429 days ago | link | parent | on: Still alive?

I use a static site generator I wrote in Arc to generate two websites. It's more fun to do that in Arc than any other language I know of.

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Thanks! The goal is to make it _way_ easier to reproduce a single test, and investigate what's going wrong.

And it's a testament to the power of Lisp that I didn't have to change much to make it happen.

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Interesting. At least for `len`, it can be fixed with a `defextend`, I believe. (https://github.com/arclanguage/anarki/blob/master/arc.arc#L2...)

To Chesterton's Fence it, though, I am not sure if templates are intended to work differently.

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3 points by zck 527 days ago | link

`len` will work with templates after this PR: https://github.com/arclanguage/anarki/pull/182

I'm leaving it unmerged for now until we can see if we can make templates work like tables for all things, except the changes we _want_.

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3 points by akkartik 527 days ago | link

I've always implicitly assumed that tables were just an implementation detail for templates, and assumed they were like objects. I think that might be why it never occurred to me to apply `len` on a template, and why a large program like news.arc never ran into this gap.

I have no objection to your approach of making them more like tables. I also have no objection to updating the documentation to stop referring to them as tables. One of those options might be less work than the other :)

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3 points by zck 526 days ago | link

> I've always implicitly assumed that tables were just an implementation detail for templates, and assumed they were like objects. I think that might be why it never occurred to me to apply `len` on a template, and why a large program like news.arc never ran into this gap.

Ah, interesting! Here's some background that might help understand why having them act like tables might help. `len` wasn't the first function that I found didn't work with templates; it was just the simplest. I was working on adding teardown functionality to unit-test.arc, and I wanted to look at some of the suites that were created, to see if I was adding tests properly. As the templates end up pretty big (one suite with two tests is about 25 lines), and it was late at night, I figured I'd make it simple on myself, and just look at the keys of the template.

This had nothing to do with the desired "production" code, but only with REPL-hacking introspection.

I want to make them reasonably easy to REPL-hack with; whether they're actually tables or not I don't particularly care right now. The most important table functions are probably len, keys, vals, and maybe maptable/each.

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2 points by akkartik 526 days ago | link

How about some rep-hacking rather than REPL-hacking? :D

   (keys rep.tem)

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3 points by zck 526 days ago | link

Haha, that certainly works. It brings up the question of "what Arc internals should people need to know about?". I've never looked into Arc's tagged types until this issue.

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2 points by akkartik 526 days ago | link

My answer to that question has always been, "it depends." The anti-encapsulation ethos (homoiconicity, using lists where other languages may use objects, the entire compiler fitting in one file and being accessible front-and-center, etc.) means that there's always the ability to peel back another layer of the onion when it becomes relevant.

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2 points by krapp 525 days ago | link

I think it's a documentation issue. I think I had to search the forums to find out about it when I was playing with JSON interop. Nowhere on the actual template page in the Arc documentation does it tell you this is a thing.

Some things I've only been able to figure out by studying the compiler or arc source code itself. Granted, that's illuminating, but it's also sometimes really annoying.

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2 points by rocketnia 525 days ago | link

"to find out about it"

Sorry, to find out about which part?

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2 points by rocketnia 524 days ago | link

Ah, I think I understand: The fact that you can call `rep` on a template instance.

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1 point by akkartik 524 days ago | link

Indeed. It never occurred to me to write about this. Would you be interested in writing something up? I can help you wrestle with the documentation system if you like.

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3 points by krapp 527 days ago | link

Templates should just enforce a signature for table fields, but otherwise decompose to tables. I think the issue is that the tables generated by (inst) from a template are annotated as type 'tem when that should (could?) be done with a tag that doesn't actually change the type. Since the template name is passed to the function, you could just build the table with default values without annotating it. You could also delete most of the template functions that just serve as template versions of table functions.

edit: I was also assuming templates type-hinted field values but I don't think they do. Maybe they should?

Also, does anyone else find it a bit odd that a language feature like this is in a lib file rather than being part of the core language?

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3 points by akkartik 527 days ago | link

Small languages take it as a mark of pride to move as much as possible into libraries :) The pitch is that the language is powerful, and nothing shows that like language features as libraries.

I was very proud in Wart that multi-branch ifs were a library feature. And check out this quote in a blog post about Forth:

    : (   41 word drop ; immediate
    ( That was the definition for the comment word. )
    ( Now we can add comments to what we are doing! )
(https://yosefk.com/blog/my-history-with-forth-stack-machines...)

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I disagree with your vision for templates. If you just want something that behaves like tables, why not just use tables? A helper that fills in default values would be pretty easy to write.

Think about the use case of news.arc. There's a list of 'objects' that need to be serialized to disk and unserialized from disk. What should happen if you change the default for a template in code? Should the default update transparently for existing objects? If so, you need some way to distinguish tables that were generated by templates. Which implies something that manages them throughout their life cycle.

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2 points by krapp 525 days ago | link

>Small languages take it as a mark of pride to move as much as possible into libraries :)

Yeah, I've seen projects that show off the power of a language by doing "x in < 100 lines" that just don't count a remote API call with half a million LOC running on a server or something ;) But with language features like macros and templates that have become ubiquitous, I feel like it's kind of cheating not to just fold them into arc proper.

But that's just me... one thing I've learned being here is that I seem to flow against the culture more than with it, so I can just agree to disagree.

> If you just want something that behaves like tables, why not just use tables?

They are tables, that's what's frustrating. They're tables with metadata. From what I can tell reading earler posts about templates, they used to be something that behaves like tables. Interop between forum data and Racket (and any code where tables are expected) is awkward because that incompatibility has to be worked around, resulting in extra code and extra complexity. Templates need a separate API despite having the same behavior as tables.

>If so, you need some way to distinguish tables that were generated by templates. Which implies something that manages them throughout their life cycle.

Fair enough. But why is it necessary to change their type to do so? Why not make this a feature of tables as a whole, if it's useful? Or tag tables in a way that doesn't change their type, if that's possible?

I understand that tradeoffs have to be made and I'm not trying to be cantankerous or dismiss the value of anyone's work, and no, I couldn't do better myself (yet), which is why I'm commenting on it it rather than making a PR. I'm just wondering if this is the best possible implementation of the concept, given how often I and other people seem to run into issues with it.

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2 points by akkartik 524 days ago | link

Don't worry about sounding dismissive, I totally understand where the questions are coming from.

Tables and objects feel like separate concepts, and they have complementary strengths and weaknesses, and one doesn't subsume the other. To me it seems obvious that if we want to have both, we need them to have different types.

For example, sometimes you want the 'dynamic' ability to set arbitrary keys of metadata on a thing. Sometimes you want the same operation to be an error, by providing a schema. How would a single type do both? No language does so, to my knowledge.

Things should have the same type when they have compatible behavior. When they are incompatible, they shouldn't.

Supporting helpers like len and keys may well still make sense. And as the original story did, this is easy to do.

But in general, having incompatible types easily share functions without sharing too much is an open problem: https://en.wikipedia.org/wiki/Expression_problem A language can easily add a method to many types, or add a new type to many methods. But we don't yet know how to achieve both sides.

And honestly, I think the expression problem isn't important. It doesn't take too much code per method/type. And making it easier just encourages large, bloated codebases.

> ...given how often I and other people seem to run into issues with it.

One thing that might be useful here is a list of issues people have encountered with templates. Maybe we should create a wiki page on GitHub and add to it every time an issue comes up. Then we can have a big-picture view of them and a sense of how many are things people need to learn about Arc, and how many are bugs to be fixed.

I believe Anarki behaves exactly the same as Arc's intent when it comes to templates. The changes that I made here seemed strictly superior to the buggy implementation upstream. But if you disagree you should absolutely feel free to just revert the commits and go back to Arc behavior. I don't use Arc anymore, so my opinions are extremely weakly held, you don't have to bother persuading me. Or, if you have some other specific issue in mind, I'd be happy to be persuaded that I'm wrong.

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2 points by rocketnia 524 days ago | link

"But in general, having incompatible types easily share functions without sharing too much is an open problem: https://en.wikipedia.org/wiki/Expression_problem A language can easily add a method to many types, or add a new type to many methods. But we don't yet know how to achieve both sides."

I'm trying to follow, but I think you and I must have different understandings of the expression problem. That article lists several known solutions to the expression problem. The solution Anarki uses is `defextend`.

What do you mean by "sharing too much"?

Is Anarki's `defextend` technique already encouraging a bloated codebase, or is there some other technique you're thinking of that would do that?

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2 points by akkartik 524 days ago | link

Yeah, I suppose you could say the problem is 'solved'. I think of it as a trade-off with costs. We don't know how to achieve zero cost.

For example, I absolutely agree with you that 2 lines per method to extend every table method to some new type constitutes a solution for us. But if we had a thousand such types and a thousand such methods, it may seem like less of a solution. But then `defextend` would be the victim rather than cause of bloat.

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3 points by rocketnia 523 days ago | link

Ah, you're imagining us having to write and maintain 1000×1000 individual `defextend` forms someday? Yeah, that does seem like a problem that would not feel solved once we got to it. :-p

I don't think that aspect of the expression problem is solvable in a language design. Instead, it's an ongoing conversation in the community. Sometimes the intent of one feature and the intent of another feature interact, leading people to do a nonzero amount of work to figure out the intent of the two features put together. That work is an essential part of what the community is trying to accomplish together, so it's a cost that can't be eliminated. The intent has to be reflected in the code somewhere, so there will be a nonzero amount of code that serves feature-coordinating purposes.

Regardless, I'm optimistic that although the amount of code will be nonzero, it'll still have a manageable size. To the extent we have any kind of consistency around these feature interaction decisions, those consistent principles can develop into abstractions. The only way we'll have 1000×1000 individual intersections to maintain is if we as a community culture are already maintaining 1,000,000 compelling and distinct justifications for them. :)

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1 point by akkartik 523 days ago | link

Indeed. I'm curious: does my interpretation of the expression problem miss what the papers tend to focus on?

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2 points by rocketnia 522 days ago | link

Well... That's a good question.

I haven't read any more than a few papers on it, and maybe only one of those in depth (which I'll mention below). Mostly I'm going by forum threads, wiki articles, and the design choices certain languages make (like Inform's multimethods and Haskell's type classes).

As far as I understand the history, Philip Wadler's work basically defined the strict parameters of the expression problem and explored solutions for it. Separate compilation and the avoidance of dynamic casts were big deals for Wadler for some reason.

That work was focused on Java, where it's easy to define new classes that implement existing interfaces but impossible to implement new interfaces on existing classes.

The solution I'm most familiar with for Java-style languages is the use of object algebras, as described in Oliveira and Cook's "Extensibility for the Masses: Practical Extensibility with Object Algebras" (https://www.cs.utexas.edu/~wcook/Drafts/2012/ecoop2012.pdf). In this approach, when you extend the system with a new type, you define a new interface with a generic type parameter and a factory method for building that type, and you have that interface inherit all the existing factory methods. So you don't have to solve the unsolvable task of implementing a new interface for an existing class, because you're representing your types as type parameters and methods, not simply as classes.

So I think the main subject of research was how best to represent an extensible program's types and functions in a language like Java where the most obvious choices weren't expressive enough. I think it's more of a "how do we allow extensions to be made at all" problem than a "how do we make all the extensions maintainable" problem.

But then, I've really barely scratched the surface of the research, so I could easily be missing stuff like that.

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2 points by akkartik 524 days ago | link

> ... with language features like macros and templates that have become ubiquitous, I feel like it's kind of cheating not to just fold them into arc proper.

Cheating how?

It's totally fine to move something into arc.arc if you want to do that. It's always felt like a non-existent distinction in my mind whether something is under arc.arc or libs/. Is Anarki all language or all standard library? Depends on how you look at it. Why does it matter?

> But that's just me... one thing I've learned being here is that I seem to flow against the culture more than with it, so I can just agree to disagree.

This doesn't feel like a disagreement, more like a language barrier. If I understood better I might know whether I agree or not.

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Yeah, just to make sure, I `git bisect`ed it down, and the behavior changed at this commit: https://github.com/arclanguage/anarki/commit/b321fb0c0273d1c...

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2 points by akkartik 544 days ago | link

Oh nice. Thank you.

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2 points by zck 541 days ago | link

Other weird thing I'm seeing:

Arc3.2:

    arc> (withs nil 3)
    3
Anarki:

    arc> (withs nil 3)
    Can't take car of nil
      context...:
       /usr/share/racket/collects/racket/private/kw.rkt:594:14:  withs
       /home/zck/programs/arc/anarki/ac.rkt:647:0: ac-call
       /home/zck/programs/arc/anarki/ac.rkt:1398:4
       eval-one-top12
This is a minimal example from something I found in unit-test.arc. It's some macros related to setup code -- if there's no setup, I currently generate something like `(withs nil 3)`. But that errors in Anarki.

You can explicitly pass no arguments. In Anarki:

    arc> (withs () 3)
    3

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2 points by akkartik 540 days ago | link

At least to me, this is expected. The commit you pointed out above switched the null value to '(). The symbol `nil` still evaluates to (). But the need for evaluation implies that it isn't available in contexts that are not evaluated, such as function arguments or in this particular slot of `withs`.

Like I said, happy to revert it if you don't like it. The whole thing came up because of this conversation: https://github.com/arclanguage/anarki/pull/145#issuecomment-.... The motivation was to simplify the Arc implementation. We already have a nil representation in the underlying Racket; it seems unnecessary to so bend over backwards to switch it to something else.

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2 points by zck 540 days ago | link

Let me figure out where in the ecosystem I'm getting the nil value from. I suspect I need to switch a bunch of usages of nil in my codebase to () or '().

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3 points by akkartik 540 days ago | link

Then again, who knows how long it will take to fix this problem. I'll roll back for now.

Edit: I feared that rolling back may also be non-trivial, but there were only some minor conflicts. Do a `git pull`! All tests are passing, and the bugs here should be fixed now.

Sorry about all this confusion and back-and-forth spanning a year. I'm going to back off on this change now. I think none of us have the bandwidth for a change this radical.

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2 points by zck 536 days ago | link

Yeah, that seems better. I'm still tracking down two test failures, but they're not because of this. I think templates now are of type 'tem, not type 'table.

I tried to make some changes to () instead of nil, and I was not a big fan of how it looked. I found it very unusual that unless quoted, parentheses mean function application. Letting () be the way to write the empty list (and I believe it worked differently quoted from unquoted, but I'm not sure offhand) completely breaks my mental model of how Lisps are parsed.

But with the revert, things look good. Thanks.

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2 points by akkartik 536 days ago | link

Great.

What are the two test failures in?

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3 points by zck 536 days ago | link

As it turns out, it's one test failure (not sure how I got the data into a weird state). It's in the test `tests-are-wrapped-to-create-test-result-template`: https://hg.sr.ht/~zck/unit-test.arc/browse/tests.arc?rev=def...

It's failing because `(type (inst 'foo))` is different in Anarki than Arc. It's a simple change to make it work; I just want to do two things before I stop looking at it:

1. Look deeper into the template inconsistencies. Thanks for the files about this in Anarki. 2. Decide if I want to cut support for Arc, or make this code work in both. This might just involve killing the test, as it's not the _most_ useful test.

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2 points by akkartik 536 days ago | link

Ouch, have the tests for unit-test.arc been failing for the past year? :( :( Very sorry about that. I see the failure now.

I somehow forgot that unit-test.arc has its own tests. Could you post the instructions for running the tests in the Readme? That would also have the salubrious side effect of showing people a way to run a bunch of existing tests.

Edit: I've added some instructions for running unit-test.arc tests to the Anarki readme: https://github.com/arclanguage/anarki/commit/0913288ec1477f2.... Hopefully that'll help remind me.

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2 points by zck 535 days ago | link

Don't worry about it! I haven't even run them in a long time, until this week -- I figured I could get teardown functionality working, then remove the hack around running Anarki tests (https://github.com/arclanguage/anarki/blob/master/tests.arc#...).

Thanks for adding the instructions.

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3 points by rocketnia 532 days ago | link

Once that last one is passing (or maybe even before it's passing), should the top-level tests.arc run these tests too? That way this can be caught not only by Travis CI, but also by people running tests.arc according to the readme.

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2 points by zck 532 days ago | link

Good question. I guess it's a question of if we have enough Anarki tests to minimze breaking changes.

If we do, then I don't know if it matters if we run unit-test.arc tests -- it's just one Arc library, presumably of several.

It's a little different than other libraries because it's what we use for Anarki unit tests.

Running it as part of Anarki's unit tests would prevent breakage, and is a simple solution to get a lot more tests added to the language. Anyone want to write a bunch of tests for Anarki itself?

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3 points by akkartik 532 days ago | link

Anarki isn't really intended to avoid or minimize breaking changes. The unit tests verify only that everything is internally consistent. That boundary around 'internal' should include unit-test.arc, I think.

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3 points by krapp 537 days ago | link

Is the problem the equality between nil and the empty list, or did that just expose some unknown flaw with the way Arc deals with macros?

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3 points by zck 534 days ago | link

I _think_ it's some weirdness with the nil/empty list thing. I was getting a case where (str x) resulted in the string "nil", but whatever that object was was not treated as nil, for example in conditionals.

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2 points by akkartik 541 days ago | link

If I found a way to "roll forward" and lose all trace of nil from the language, would that be acceptable?

(I tried briefly but haven't managed it yet. So it's probably faster to just roll back. I'm just curious about the question.)

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2 points by zck 540 days ago | link

Interesting concept. I feel like I'd be ok with it? I want to say we should bind `nil` to `'()`, so existing code would continue to work, but I might be overindexing on compatability and what I'm used to.

I will admit to not being super sure what the real differences between nil and '() are. Presumably it's more than "what is the human-readable representation of the value that terminates a list/is the false value". But I'm not sure what. Also, is there a difference between the quoted and unquoted version? It feels odd to write () in a repl unquoted -- usually, I expect parens to mean a function or macro call.

Prior discussions I've found:

* https://github.com/arclanguage/anarki/pull/145#issuecomment-... * http://arclanguage.org/item?id=11723 (ten years ago Tuesday!) indicates using '() helps with Racket interop * http://arclanguage.org/item?id=21047

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