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Poll: Which library should we focus on first?
7 points by shader 3778 days ago | 30 comments
The previous poll determined hands down that adding libraries deserved the highest community attention. Though some people reasonably stated that we should write real programs first and then determine what libraries are needed, some libraries are so commonly used that we can reasonably implement them first. An example would be a basic math library, with sin, cos, pi, gcd, etc. These are very standard functions, so they don't require much design work / use to figure out what the interfaces should be.

So I've compiled a short list of libraries and tools, some of which have been taken from the Libraries TODO list on Anarki's git wiki.

Which do you think we should do "first"? Note that voting for a library is almost the same as offering to work on it :)

7 points
8 points
Graphics: e.g. SDL, OpenGL, DirectX, etc.
5 points
Web tools: xml parser, screen scraping, rss, arc-to-javascript, etc.
17 points
Regex / string manipulation
10 points
Object system
5 points
Image manipulation
1 point
14 points
Unit testing
2 points
Module System
3 points

8 points by Darmani 3778 days ago | link

Well, since I voted for the basic library with sin, cos, pi, gcd, etc, I felt obligated to implement a basic math library with sin, cos, pi, gcd, closely related fucntions, and everything I needed or thought I'd need to implement those.

Implementations guaranteed not to be optimally efficient:

Edit: Fixed a mistake in bringing out-of-period numbers into period in sin and cos

  (= pi 3.141592653589793238)
  (= 2*pi (* 2 pi))
  (def signum (n)
    (if (> n 0)
      (< n 0)
  (def floor (x)
    (if (< x 0)
      (- (trunc x) 1)
      (trunc x)))
  (def ceil (x)
    (if (< x 0)
      (trunc x)
      (+ (trunc x) 1)))
  (defmemo fac (n)
    (if (is n 0)
      (* n (fac (- n 1)))))
  ;Existing mod only accepts integers. Left intact as "modulo"
  ;This mod copies the behavior of Ruby's mod
  (def mod (dividend divisor)
    "Returns the remainder from dividing dividend by divisor.
    Adds divisor once more if they are of different signs so that the result is always of the same sign as divisor."
    (if (is divisor 0)
          (error "modulo undefined for 0")
        (isnt (signum dividend) (signum divisor))
          (+ divisor (- dividend (* divisor (trunc (/ dividend divisor)))))
          (- dividend (* divisor (trunc (/ dividend divisor))))))
  (def sin (x)
    "Returns the sine of x in radians."
      (let x (let red (mod x 2*pi)
                (if (> (abs red) pi)
                  (- red (* (signum red) 2*pi))
         ;Taylor polynomial; 0.0 is to cast to float
         (- (+ 0.0 x (/ (expt x 5) (fac 5)) (/ (expt x 9) (fac 9)))
             (/ (expt x 3) (fac 3)) (/ (expt x 7) (fac 7)))))
  (def cos (x)
    "Returns the cosine of x in radians."
       (let x (let red (mod x 2*pi)
                 (if (> (abs red) pi)
                   (- red (* (signum red) 2*pi))
         ;Taylor polynomial
         (- (+ 1.0 (/ (expt x 4) (fac 4)) (/ (expt x 8) (fac 8)))
             (/ (expt x 2) (fac 2)) (/ (expt x 6) (fac 6)))))
  (def tan (x)
    "Returns the tangent of x in radians."
    ;Lazy definition
    (/ (sin x) (cos x)))
  (def int? (x)
    "Returns whether x is an integer"
    (is (mod x 1.0) 0.0))
  (defmemo prime (n)
    "Returns the nth prime. 2 is the 0th prime."
    (if (< n 0)
        (is n 0)
          (let prev-primes (map prime (range 0 (- n 1)))
              ((afn (i)
                  (if (no (breakable:each p prev-primes ;Each always returns nil, so a break returns t
                              (if (int? (/ i p))
                                (break t))))
                        (self (+ i 1))))
                (+ 1 (last prev-primes))))))
  (def prime-factorization (n)
    "Returns a list each prime up to the greatest prime in n paired with the power of that prime in n.
    E.g.: (prime-factorization 20) returns ((2 2) (3 0) (5 1)).
    Use (reduce * (map [apply expt _] ...)) to change a prime factorization into the number."
    (rev:accum keep
      (let p-ord 0
        (while (> n 1)
            (with (p (prime p-ord)
                    pow 0)
              (until (isnt (mod n p) 0)
                (++ pow)
                (zap [/ _ p] n))
              (keep (list p pow)))
            (++ p-ord)))))
  (def gcd (x y)
    "Returns the greatest common divisor of x and y."
      (reduce * (map [apply expt _]
          (map (fn (a b)
                    (list (car a) (min (cadr a) (cadr b))))
            (prime-factorization x) (prime-factorization y)))))
  (def lcm (x y)
    "Returns the least common multiple of x and y."
    (/ (* x y) (gcd x y)))


4 points by shader 3778 days ago | link

Nice. I only did the gcd function, so you've got an amazing head start on me. However, the version of gcd that I did was Euclid's algorithm. Probably faster than prime factorization; and I included a case for only one number, and a list of greater than two.

Since I couldn't commit to github for some reason, here's the code:

  ;;Int (predicate)
  (def int (n)
    "Returns true if n is an integer; i.e. has no decimal part."
    (is (trunc n) n)) ; return true if the number is the same as itself without the decimal part

  ;;Greatest Common Denominator
  (def gcd l
    "returns the greatest common denominator, or divisor, of a list of numbers. Numbers should be integers,
     or the result will default to 0."
    (with (a (car l) c (cdr l))
      (if (len> c 1) 
            (gcd a (gcd (car c) (cdr c))) ; handle lists of more than two numbers
          (no a) 0
          (no c) (abs a)
          (let b (car (flat c))
            (if (or (~int a) (~int b)) 0 ; skip non-integers
                (is a b) a ; return common divisor
                (if (> a b)
                      (gcd (- a b) b)
                    (gcd (- b a) a)))))))

Figured out what I was doing wrong with github. Math library now started in lib/math.arc. Currently it only contains my gcd function and the 'int test, but feel free to add any other math functions.

In the future, we may need to make it a math folder, with individual files for trig functions, hyperbolic functions, calculus, matrix and vector function, quaternions, etc. But for now one file is more than enough to contain my lowly gcd :)


1 point by Darmani 3778 days ago | link

  arc>(def int (n)
    (is (trunc n) n))
  #<procedure: int>
  arc>(int 1.0)
My original int? was identical to yours, but that's why I changed it. Although, now that I think about it, since prime-factorization discards the results of operations that cast n to a rational, that's unnecessary. Still, there will need to be separate functions for testing if a num's type is int (which yours does), and testing if a num lacks decimal places (which mine does).

(And yes, Euclid's is definitely faster than prime factorization -- I originally looked at better algorithms for prime finding and gcd but I decided to settle for the "pure" approach -- sieve instead of some Fermat's or another fast primality test, prime factorization based instead of Euclid's.)

P.S.: Feel free to make use of the code I posted.


1 point by shader 3778 days ago | link

Ah, I didn't notice that. Apparently I should test things more carefully next time :)

I don't know if you have github access, but if you do, you can feel free to add your own code to the math.arc lib. I probably won't have a chance to add it myself in the next week or so. If I can, though, I will definitely try to do so.


2 points by eds 3775 days ago | link

I just pushed 'floor, 'ceil, and 'fac from, and 'sin, 'cos, and 'tan to Anarki.

In doing so, I noticed one bug in Darmani's original implementation of 'floor and 'ceil. 'floor would return incorrect results on negative integers (e.g. (floor -1) => -2), and 'ceil on positive integers (e.g. (ceil 1) => 2). This has been corrected on Anarki.

I also used mzscheme's 'sin, 'cos, and 'tan instead of Darmani's, not because of speed issues, but because of decreased precision in those functions. In order to get maximum precision it would be necessary to calculate the Taylor series an extra couple of terms, which I didn't feel like doing at the time.

I didn't commit 'signum, 'mod, 'prime, or 'prime-factorization, because I wasn't sure if they were needed except for computing 'sin, 'cos, and 'gcd... but feel free to commit them if you want.


1 point by shader 3766 days ago | link

I have a few questions:

1) Isn't pushing those math functions straight from scheme sort of cheating? I mean, maybe I'm just wrong, but wouldn't the solution be more long term if we avoided scheme and implemented the math in arc?

2) Shouldn't fac be tail recursive? Or is it, and I just can't tell? Or are you just expecting that no one will try and compute that large of a factorial

3) If some one did compute that large of a factorial, is there some way for arc to handle arbitrarily sized integers?


1 point by almkglor 3766 days ago | link

1) No, you should implement in the math in the underlying machine instructions, which are guaranteed to be as precise and as fast as the manufacturer can make it. The underlying machine instructions are fortunately possible to access in standard C libraries, and the standard C library functions are wrapped by mzscheme, which we then import in arc.

2) It should be, and it isn't.

  (defmemo fac (n)
    ((afn (n a)
       (if (> n 1)
           (self (- n 1) (* a n))
     n 1))
3) Yes, arc-on-mzscheme handles this automagically. arc2c does not (I think it'll overflow)


3 points by kens 3766 days ago | link

Implementing numerically stable and accurate transcendental functions is rather difficult. If you're going down that road, please don't just use Taylor series, but look up good algorithms that others have implemented. One source is

That said, I don't see much value in re-implementing math libraries in Arc, given that Arc is almost certainly going to be running on a platform that already has good native math libraries.


1 point by shader 3766 days ago | link

I figured that being close to machine instructions was a good thing, but I thought that we should do that via some other method, not necessarily scheme, which may or may not remain the base of arc in the future.

That being said, if you think that pulling from scheme is a good idea, why don't we just pull all of the other math functions from there as well?


2 points by almkglor 3766 days ago | link

> That being said, if you think that pulling from scheme is a good idea, why don't we just pull all of the other math functions from there as well?

Yes. Yes it is.

That's what I said ^^


1 point by shader 3765 days ago | link

Ok, I added that tail optimized version to math.arc.

Do you want to have a separate math libs for the scheme functions and native implementations? You already suggested the possibility.


2 points by almkglor 3765 days ago | link

Err, "native implementations" being?

Actually I think it might be better if we had a spec which says "A Good Arc Implementation (TM) includes the following functions when you (require "lib/math.arc"): ...." Then the programmer doesn't even have to care about "scheme functions" or "java functions" or "c functions" or "machine language functions" or "SKI functions" - the implementation imports it by whatever means it wants.

Maybe also spec that the implementation can reserve the plain '$ for implementation-specific stuff.


4 points by almkglor 3778 days ago | link

Interesting, you actually defined it mathematically ^^

It might also be useful to create a lib/mz-fast-math.arc which just imports 'sin, 'cos, 'tan from mzscheme using '$


1 point by jmatt 3776 days ago | link

I think that's a good idea.


4 points by stefano 3777 days ago | link

If someone wants to implement an IDE for Arc, or any other desktop (as opposed to web-based) application a GUI library is essential. I had already started the job some time ago by writing a simple GTK binding (very few function at the moment) on Anarki. We could use it as a back-end for a more Arc-ish GUI library.


1 point by conanite 3777 days ago | link

an IDE is coming! if you don't mind it being in java, that is ...


1 point by almkglor 3776 days ago | link

How about in Rainbow? Is it implementable there?


4 points by conanite 3776 days ago | link

i'm working on it. hope to post news this weekend. it's also my daughter's birthday, she's 2 tomorrow :)


1 point by almkglor 3775 days ago | link

LOL. Hope it goes well ^^


1 point by oconnor0 3776 days ago | link



1 point by oconnor0 3776 days ago | link

Ah, that Rainbow...


12 points by almkglor 3778 days ago | link

A module system to organize them all?


5 points by stefano 3777 days ago | link

This is really necessary, especially if we want to keep using short names and not something like:

  (gui-window-set-title w "my title")


2 points by shader 3778 days ago | link

I've already started on the math library, beginning with the gcd function.

Unfortunately, I'm not that good at arc yet. How do you make a function that will take 0 or more arguments, instead of requiring at least one?


8 points by cchooper 3778 days ago | link

Like this:

  (def foo args
    (prn args))

  => nil

  (foo 1)
  => (1)

  (foo 1 2)
  => (1 2)


3 points by markokocic 3775 days ago | link

Slime support would be nice. Some schemes and clojure already have some sort of slime integration.


2 points by jimm 3765 days ago | link

See lib/mysql-ffi.arc in Anarki for a simple MySQL interface.


1 point by wgac 3529 days ago | link

Here are definitions of the basic trigonometric functions alternative to the Taylor series. They use complex numbers and Euler's formula. By the way, could someone tell me how to make my code stand out in a comment? Thanks.

(= e 2.71828182845904523539)

(= pi 3.14159265358979323846)

(def sin (x) (/ (- (expt e (* 0+1.i x)) (expt e (* 0-1.i x))) 0+2i))

(def cos (x) (/ (+ (expt e (* 0+1.i x)) (expt e (* 0-1.i x))) 2.0))

(def tan (x) (/ (sin x) (cos x)))

(def cot (x) (/ (cos x) (sin x)))


1 point by thaddeus 3529 days ago | link

I'm assuming when you say 'standout' you mean format/indent your line breaks for code.... for that you add 4 spaces before each line of code. If you mean standout = bold, no clue. T.


1 point by wgac 3528 days ago | link