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Apologies for the frequent downtime (tryarc.org)
2 points by evanrmurphy 4737 days ago | 33 comments


4 points by zck 4736 days ago | link

Thanks for hosting this site in the first place! It's really useful. Is there anything I can do to help out?

Last I checked, you couldn't paste into the repl (I can't check now, unfortunately, as it's down). That feature will make a huge difference to me -- my main use case for tryarc.org is telling people about arc, and they won't type in an example I give them, especially if it's more than a two-line toy. What needs to happen to get this to work? Again, can I help?

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5 points by evanrmurphy 4736 days ago | link

Good news - copy and paste is finally working now (just fixed it). So now people will be able to paste in your examples! :-)

Thank you for the encouraging/motivating comment! Fixing copy-paste has been on my list for a long time, but this finally got me to do it.

I appreciate your offer to help. Maybe I should open-source Try Arc and then people can start issuing pull requests when they're motivated to fix something.

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2 points by zck 4736 days ago | link

Awesome! That'll really help me show people arc code, as I'm rarely at a computer with Arc installed when I want to show people.

Open-sourcing Try Arc would be cool. I'd love to look at larger Arc projects -- all of mine are middling at best. I'm working on bigger ones, but the lack of libraries is...frustrating, so I'd love to see how other people work with Arc.

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2 points by akkartik 4736 days ago | link

I'm curious: who are these people you're showing arc to and how do you find them on a regular basis? ^_^

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2 points by zck 4736 days ago | link

Generally, I'll try to show it to some of my programmer friends, or to people at work.

I had actually come up with an interview question: take two strings and return the index of the first difference. I posted some arc code, and wanted to have people run it.

My code:

  (def first-difference (seq1 seq2 (o comparer is))
       "Returns the index of the first difference between seq1 and seq2, or nil if
        they are the same. This function uses 'comparer as the function to compare
        elements of the sequences."
       (withs (len1 (len seq1) ;; 'withs ([var1 val1]* ) binds each var to its val
               len2 (len seq2)
               helper (afn (seq1 seq2 pos) ;; 'afn makes an anonymous function that
                                           ;; can recurse by calling 'self
                           (if (is len1
                                   len2
                                   pos) ;; at end of both sequences
                               nil
                             (or (is len1
                                     pos)
                                 (is len2
                                     pos)) ;; at end of only one sequence
                             pos
                             (~comparer seq1.pos
                                        seq2.pos) ;; found a difference
                             pos
                             (self seq1 seq2 (+ pos 1)))))
               (helper seq1 seq2 0)))

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2 points by akkartik 4736 days ago | link

Nice example. For exposition is it useful to simplify the problem by focusing on lists?

  (def first-difference(seq1 seq2)
    (if (or no.seq1 no.seq2
            (~iso car.seq1 car.seq2))
      0
      (+ 1 (first-difference cdr.seq1 cdr.seq2))))
Edit: no, that's not right, because it doesn't return nil on identical sequences. Here are two variants with and without the accumulator. Which is easier for noobs?

  (def first-difference(seq1 seq2 (o pos 0))
    (if
      (and no.seq1 no.seq2)
        nil
      (or no.seq1 no.seq2 (~iso car.seq1 car.seq2))
        pos
      'else
        (first-difference cdr.seq1 cdr.seq2 (+ pos 1))))

  (def first-difference(seq1 seq2)
    (if
      (and no.seq1 no.seq2)
        nil
      (or no.seq1 no.seq2 (~iso car.seq1 car.seq2))
        0
      'else
        (only.+ (first-difference cdr.seq1 cdr.seq2) 1)))
 
  (test-iso "" 0 (first-difference nil '(34)))
  (test-iso "" nil (first-difference '(1) '(1)))
  (test-iso "" 1 (first-difference '(1) '(1 2)))
  (test-iso "" 3 (first-difference '(1 2 3 4) '(1 2 3)))

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1 point by jsgrahamus 4735 days ago | link

  arc> (def 1st-diff (str1 str2 i)
    (if (or (is str1 "") (is str2 ""))
      0
      (or (> i (- (len str1) 1)) (> i (- (len str2) 1)))
      i
      (no (is (str1 i) (str2 i)))
      i
      (1st-diff str1 str2 (+ i 1))))
  #<procedure: 1st-diff>
  arc> (1st-diff "" "" 0)
  0
  arc> (1st-diff "" "" 0)
  0
  arc> (= astring "abcde")
  "abcde"
  arc> (= bstring "abced")
  "abced"
  arc> (1st-diff "" "" 0)
  0
  arc> (1st-diff astring "" 0)
  0
  arc> (1st-diff "" astring 0)
  0
  arc> (1st-diff astring bstring 0)
  3
  arc> (1st-diff bstring astring 0)
  3
  arc> (1st-diff astring "abcdef" 0)
  5
  arc> (1st-diff "abcdef" astring 0)
  5
  arc>

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1 point by jsgrahamus 4735 days ago | link

It's interesting to compare this to the solution in my workday language. One of the reasons that M is shorter is because its functions are more tolerant. For arc, I had to make sure that the index to the string was not too large. In M, it simply returns an empty string if you attempt to access a string position beyond the length. And I used iteration with M. Perhaps the arc solution would have been shorter had I done the same there.

Interesting exercise for this newbie.

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2 points by akkartik 4735 days ago | link

Yeah you can index past the end in my arc variant (http://github.com/akkartik/wart). But it currently returns nil. What should it be?

I'd love to see the M version expanded into english.

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2 points by jsgrahamus 4735 days ago | link

Great.

I'm used to seeing it as the empty string

Here is the expanded M version (! = LF):

  IF X=Y WRITE !,0 ; No difference
  ELSE  FOR I=1:1 IF $EXTRACT(X,I)'=$EXTRACT(Y,I) WRITE !,I QUIT

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1 point by akkartik 4734 days ago | link

I still don't know enough MUMPS to follow it :)

Are you concatenating strings? Is that where returning "" is useful? In wart concatenating strings is tolerant of non-strings, so I think returning nil should be ok.

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2 points by jsgrahamus 4733 days ago | link

If the string X = the string Y, print 0 (to indicate there are no differences / MUMPS uses 1-based indexing of strings)

Otherwise, go through each character of the strings and at the point where they differ, print that index and quit looping.

MUMPS does not error out on attempting to extract a character beyond the string's length. So in that event, 1 string's extract will return the empty string, which will differ from the other string's extract and will cause you to print the index and quit. Not generating such an error, of course, cuts down on the code needed.

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2 points by zck 4733 days ago | link

So if we enter the for loop, we know there is a difference between the two sequences.

So we just need to find an index position i where (isnt seq1.i seq2.i) is true. If indexing off the end of a string causes an error, we need to put in code to prevent that. If indexing off the end of a string returns anything that can't be an element of the string, we can compare each index i until we find a difference, knowing that we'll eventually find one.

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1 point by jsgrahamus 4733 days ago | link

Correct.

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1 point by jsgrahamus 4735 days ago | link

test-iso?

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1 point by akkartik 4735 days ago | link

https://github.com/nex3/arc/blob/ec47676f99af11b6fa8935a3cb0...

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3 points by jsgrahamus 4736 days ago | link

In my work language:

  I X=Y W !,0 ; No difference
  E  F I=1:1 I $E(X,I)'=$E(Y,I) W !,I Q
A challenge for me is arc/lisp/scheme's verboseness.

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1 point by akkartik 4736 days ago | link

What is that, J?

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1 point by rocketnia 4736 days ago | link

I think you may already have an inkling somewhere in the back of your mind.... http://arclanguage.org/item?id=15341

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1 point by akkartik 4735 days ago | link

Lol.

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1 point by jsgrahamus 4735 days ago | link

MUMPS / M / Caché - Used it for most of 30 years. In the U.S. mostly used on medical information systems, however it is also used in banks, credit unions, Ameritrade, etc.

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2 points by jsgrahamus 4736 days ago | link

Can you employ Racket's libraries for what you need?

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1 point by zck 4735 days ago | link

Some of it. What I've been working on lately is trying to get the Twitter API to work with Arc. I haven't found any Racket libraries for Twitter or even for OAuth. I would be very excited to find one, though -- this project has been [stuck](http://arclanguage.com/item?id=16040) for [way](http://arclanguage.com/item?id=15207) too [long](http://arclanguage.com/item?id=14817).

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1 point by evanrmurphy 4736 days ago | link

That worked for me with Try Arc. It's really not a large program, the portion that I wrote. On the backend, all the heavy lifting is done by Racket's sandbox library and srv.arc. On the front-end, it's Chris Done's jQuery console (and to some extent now, WordPress).

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3 points by akkartik 4736 days ago | link

Hells yeah!

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1 point by evanrmurphy 4737 days ago | link

I just wanted to apologize for the frequent downtime that has been occurring at Try Arc (you may or may not have noticed). I hope it hasn't inconvenienced too many people trying to hack on Arc while away from their installations or newcomers just getting started. I know at least one time zck was unable to test some code because of it (http://arclanguage.org/item?id=15207).

Thanks for your patience while I get this figured out.

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2 points by jsgrahamus 4735 days ago | link

I haven't experienced the downtime. However, I would like to use it on my Android, but the Enter key does not seem to end the input line. Any ideas on how to handle that?

Thanks, Steve

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1 point by evanrmurphy 4735 days ago | link

Hi Steve, have you had a chance to try this on your Android since yesterday? I think the update I made to fix copy-paste may have also fixed this.

The reason I say this is that I just tried it on my Android - a Samsung/Google Nexus S - and it worked (the Enter key did successfully end the input line). But it may also be due to us having different phones, so when you get a chance to try it out again, please let me know.

Also, thanks for your patience and for reminding me about this issue. I remember you first raising it a long time ago.

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1 point by jsgrahamus 4735 days ago | link

I have a T-Mobile G-1 and it does not terminate the line. Perhaps because I have version 1.6.

You're welcome of course.

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1 point by evanrmurphy 4734 days ago | link

Ok, thanks. I've created an issue for this in the Feedback forum, which is my running todo list for try arc: http://tryarc.uservoice.com/forums/80605-general/suggestions...

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1 point by evanrmurphy 4736 days ago | link

I think it turns out that my Linode just needed more memory. I added some a few minutes ago, we'll see if that fixes the problem.

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1 point by akkartik 4737 days ago | link

Lol, that blog post seems down right now :)

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1 point by evanrmurphy 4737 days ago | link

Strange. Haven't noticed that go down, try again :-)

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