Arc Forumnew | comments | leaders | submitlogin
4 points by shawn 2134 days ago | link | parent

I switched `(write ...)` to `(pretty-print ...)` for repl values. https://github.com/arclanguage/anarki/pull/142

Let me know if that seems sufficient for now.

You're right that Arc still can't read tables written via `write`. That is definitely worth supporting. Here is an example of how it could work: https://github.com/sctb/lumen/blob/55b14ca8aafeaf6b0ca1b636d...

It would be important to ensure that circular structures don't cause an infinite loop, and I'd be nervous about straying too far from Racket's `write` facility. For better or worse, it's a limitation of racket that you can't `read` a table you've written. But it could be worth doing.



3 points by rocketnia 2134 days ago | link

"it's a limitation of racket that you can't `read` a table you've written"

Eh? You definitely can, in Racket. :) The only problem I know of is that when you write a mutable table, you read back an immutable one.

---

"You're right that Arc still can't read tables written via `write`."

Arc's supported this for as long as I can remember. The only problem is that they come back immutable.

Here's Arc 3.2 on Racket 7.0:

  arc> (= foo (fromstring (tostring:write:obj a 1 b 2) (read)))
  #hash((a . 1) (b . 2))
  arc> (= foo!a 3)
  Error: "hash-set!: contract violation\n  expected: (and/c hash? (not/c immutable?))\n  given: '#hash((a . 1) (b . 2))\n  argument position: 1st\n  other arguments...:\n   'a\n   3"
And here's the latest Anarki:

  arc> (= foo (fromstring (tostring:write:obj a 1 b 2) (read)))
  '#hash((a . 1) (b . 2))
  
  arc> (= foo!a 3)
  3
  
  arc> foo
  '#hash((a . 3) (b . 2))
Oh, I guess it works!

It looks like that's thanks to a March 8, 2012 commit by akkartik (https://github.com/arclanguage/anarki/commit/547d8966de76320...)... which, lol... Everything I was saying in a couple of recent threads about replacing the Arc reader to read mutable tables... I guess that's already in place. :)

-----

4 points by kinnard 2132 days ago | link

It'd be cool if this worked with curly brace syntax. You could read in (and write) a file that looked like this:

  {'id 3 
   'c {
      'name "james c clarke" 
      'age 23 
      'addr "1724 Cox Ave. NY, NY 90210"
     }
  }
I think it'd make reading and writing a much better experience.[1]

[1] http://arclanguage.org/item?id=20803

EDIT: I guess this would be called "table literals"?

-----

2 points by kinnard 2131 days ago | link

Does the necessity of quasiquote + unquote feel natural?

  (= tpipe {todo 
              '({id 1 cont "get eggs" done '(nil)}
                {id 23 cont "fix toilet" done '(nil)})
            week '(nil)
            today '({id 83 cont "Build something that works in arc" done '(nil)})
This won't work:

  arc> tpipe!todo.1!id
One must employ (list) or quasiquotation

    (= npipe {todo 
                (list {id 1 cont "get eggs" done '(nil)}
                      {id 23 cont "fix toilet" done '(nil)})
              week '(nil)
              today (list {id 83 cont "Build something that works in arc" done '(nil)})
              done (list {id 44 cont "Research Ordered Associative Arrays" done '(2019 1 21)})})

    (= unqpipe {todo 
                `(,{id 1 cont "get eggs" done '(nil)}
                  ,{id 23 cont "fix toilet" done '(nil)})
                week '(nil)
                today `(,{id 83 cont "Build something that works in arc" done '(nil)})
                done `(,{id 44 cont "Research Ordered Associative Arrays" done '(2019 1 21)})})

-----

3 points by rain1 2122 days ago | link

I think you should have to quote them. Like how you have to quote lists:

    '(foo bar)
is just a list, but

    (foo bar)
will either call the function foo or error if it doesn't exist.

So in a similar way

    {foo "bar"}
should give a syntax error, but maybe it can have some kind of semantic meaning later. I've been considering that square brackets could be used for assignment/local binding, to cut down on the need for LET (not necessarily in arc just in lisp in general).

-----

2 points by i4cu 2122 days ago | link

> should give a syntax error...

I don't agree. quoting a list is a way to protect the expression from evaluation, in this case because round brackets normally indicate an expression that needs to be called. A table literal {...} doesn't need protection from evaluation as a callable expression as it's just data and like any other data it should evaluate to itself. And, frankly, it would really suck having to protect that data everywhere in my code because someone wants a really nuanced use case to work.

Really what should happen is that [] should be implemented such that we don't need to protect lists of data.

-----

2 points by i4cu 2122 days ago | link

> Really what should happen is that [] should be implemented such that we don't need to protect lists of data.

I should point out that I don't think this can happen since square brackets are reserved for other uses in Arc.

-----

2 points by rain1 2122 days ago | link

I see what you mean, making it self evaluate seems like the best option.

-----

2 points by krapp 2121 days ago | link

>For better or worse, it's a limitation of racket that you can't `read` a table you've written. But it could be worth doing.

I've been trying to get the tables generated by the personal data link in news to export as JSON for a while now[0]. Part of the problem seems to be related to this - Racket doesn't seem to know what to do with #tagged tem or #hash (much less nils.)

[0]https://github.com/arclanguage/anarki/blob/master/apps/news/...

-----