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?
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.
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.
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)))
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?
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.
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.
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.
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.
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).
