Hi Raul - is there someplace I can see this flip code in action?
I recently attended a big talk on the Julia programming language but I left after about 40 minutes as it looked like another dog's breakfast of a language, e.g. they use " X ' " to transpose "X" because it looks like one of the math notations for doing this. The one good thing I got out of the talk was when they showed a table comparing Julia to other languages in terms of performance for various "standard" tasks - like finding primes and Fibonacci numbers. Of course, their language was better than R and Matlab, sometimes by a large margin, but what really stood out for me is that Javascript was as good or better than Julia for many of the tasks. That motivated me to start learning Javascript, so I'm glad to see non-trivial examples like you show here. Regards, Devon On Wed, May 9, 2012 at 9:22 AM, Raul Miller <[email protected]> wrote: > I was amused by this: > > "Arguably it's the nicest programming environment I've ever used, > even though I go back and forth about whether J itself is brilliant or > insane." > > http://prog21.dadgum.com/28.html > > In an unrelated conversation, someone I know complained about APL > syntax, and I pointed out that the case he was talking about had no > unusual syntax -- it was bog-standard expression syntax, just like any > other language's expression syntax. It was just the symbols and their > definitions being different. > > And, he said "yes" -- that when he said "syntax" he really meant the > semantics. > > Meanwhile, in a completely different context, I was building some > "flip" code for javascript. There are numerous jquery plugins that > deal with "flipping" content -- giving an effect like rotating it on a > 3d plane. But I wanted to be able to flip on an arbitrary axis. > After a bit of investigation, I decided to use the css3 2d matrix > operations -- that gave me compatibility with IE9, chrome, firefox and > a few others (but not IE8, so users of windows XP would have to use > something other than IE to get this effect). > > After struggling with various implementations, I finally fell back on > how I would do it in J. Leaving out the jQuery animate stuff, the > code looks like this: > > function do_rotate(target, axis, angle, X, Y) { > var m= inner_product( > translate(X, Y), > inner_product( > rotxy(axis), > inner_product( > rotyz(angle), > inner_product( > rotxy(-axis), > translate(-X, -Y))))); > var matM= cssmatrix(m, 1); > var matG= cssmatrix(m, 0); > target.css({ > 'transform': matG, > '-moz-transform': matM, > '-ms-transform': matG, > '-o-transform': matG, > '-webkit-transform': matG > }); > }; > function op(f, m1, m2) { > var r= []; > if ('object' != typeof m1) > if ('object' != typeof m2) > r= f(m1, m2); > else > for (var j= 0; j < m2.length; j++) > r[j]= op(f, m1, m2[j]); > else > if ('object' != typeof m2) > for (var j= 0; j < m1.length; j++) > r[j]= op(f, m1[j], m2); > else > for (var j= 0; j < m2.length; j++) > r[j]= op(f, m1[j], m2[j]); > return r; > } > function add(m1, m2) { > return op(function(x, y) {return x+y}, m1, m2); > } > function mul(m1, m2) { > return op(function(x, y) {return x*y}, m1, m2); > } > function sum(m) { > var r= 0; > for (var j= 0; j < m.length; j++) > r= add(r, m[j]); > return r; > } > function inner_product(m1, m2) { > var r= []; > for (var j= 0; j < m1.length; j++) > r[j]= sum(mul(m1[j], m2)); > return r; > } > function translate(x, y) { > return [[1, 0, 0, x], [0, 1, 0, y], [0, 0, 0, 1], [0, 0, 0, > 1]]; > } > function rotxy(angle) { > var c= Math.cos(angle); > var s= Math.sin(angle); > return [[c, -s, 0, 0], [s, c, 0, 0], [0, 0, 0, 1], [0, 0, 0, > 1]]; > } > function rotyz(angle) { > var c= Math.cos(angle); > var s= Math.sin(angle); > return [[1, 0, 0, 0], [0, c, -s, 0], [0, s, c, 0], [0, 0, 0, > 1]]; > } > function cssmatrix(m, moz) { > moz= moz ?'px' :0; > return 'matrix('+[m[0][0], m[1][0], m[0][1], m[1][1], > m[0][2]+moz, > m[1][2]+moz].join(',')+')'; > } > > And that was enough for me to get where I wanted to be. > > Here, function op() gives me the ability to have javascript functions > which behave like J rank 0 dyadic verbs. And, inner_product is J's +/ > .* as long as the left argument has a rank no greater than 2. (In > real life, J's implementation is not so recursive -- I think that the > recursion in op() has more to do with javascript's array data > structures than with J.) > > Anyways, I think my point here is that everything J does is simple -- > dead simple. > > It's difficult, though, sometimes, conveying just how simple this stuff is. > > -- > Raul > ---------------------------------------------------------------------- > For information about J forums see http://www.jsoftware.com/forums.htm -- Devon McCormick, CFA ^me^ at acm. org is my preferred e-mail ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
