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var List = function() {
  return (function build(xs) {
    if(xs.length === 0) return Nil
    return new Cons(xs[0], build(Array.prototype.slice.call(xs, 1)));
  })(arguments);
}

var Nil = {
  head: null,
  tail: null,

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var Empty = {
  contains:  function(x)     { return false; },
  incl:      function(x)     { return new NonEmpty(x, Empty, Empty); },
  union:     function(other) { return other; },
  toString:  function()      { return '.'; }
};

var NonEmpty = function(elem, left, right) {

  return {

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Sorting = {

  insert_sort: function(xs) {

    function insert(x, xs) {
     if(xs.length === 0) return [x];
     else return x <= xs[0] ? [x].concat(xs) : [xs[0]].concat(insert(x, xs.slice(1)));
    }

    return xs.length === 0 ? [] : insert(xs[0], this.insert_sort(xs.slice(1)));

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Object.prototype.isEqual = function(obj) {

  function iter(a, b) {
    for(p in a) {
      if(a.hasOwnProperty(p)) {

        if(!b.hasOwnProperty(p)) return false;

        else if(['array', 'object'].indexOf(typeof b[p]) > -1) {
          if(!iter(b[p], a[p])) return false;

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scale = function(a,d) { return a.map(function(x) { return (x - avg(a)) / d}) }

avg = function(a) { return sum(a) / a.length }
sum = function(a) { return a.reduce(function(x,y) { return x + y; }) }
max = function(a) { return a.sort(function(x,y) { return x < y; })[0] }
min = function(a) { return a.sort(function(x,y) { return x > y; })[0] }
sd = function(a,av) { return Math.sqrt(avg(a.map(function(x) { return (x - av) * x; }))); }

z = [20,25,10,33,50,42,19]
scale(z,(max(z) - min(z))) // [-0.2107142857142857, -0.23571428571428568, -0.2107142857142857, -0.08571428571428567, 0.11428571428571432, 0.3392857142857143, 0.5392857142857144]

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zipw = function(a,b,f) {
	var c = a.length < b.length ? {a:a, b:b} : {a:b, b:a};
	return c.a.map(function(x,i) {
		return f(x,c.b[i]);
	});
}
zipw([1,2,3],[10,11,12], function(x,y) { return x + y; }); // [11,13,15]
zipw([1,2,3],[10,11,12], function(x,y) { return x * y; }); // [10,22,36]

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mmultiply = function(a,b) {
	return a.map(function(x,i) {
		return transpose(b).map(function(y,k) {
			return dotproduct(x, y)
		});
	});
}

dotproduct = function(a,b) {
	return a.map(function(x,i) {

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function im(n) { var a = Array.apply(null, new Array(n)); return a.map(function(x, i) { return a.map(function(y, k) { return i === k ? 1 : 0; }) }) }

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function text2bin(msg) { return msg.split('').map(function(x) { var b = x.charCodeAt(0).toString(2); return Array(9 - b.length).join(0) + b; }).join(''); }

function bin2text(bin) { return bin.match(/(.{1,8})/g).map(function(x) { return String.fromCharCode(parseInt(x, 2)) }).join(''); }

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calculate = function(a, f) { return a.reduce(function(x,y) { return f(x, y) }); }

sum = function(a, b) { return a + b; }
sub = function(a, b) { return a - b; }

sumAll = function(a) { return calculate(a, sum); }
subAll = function(a) { return calculate(a, sub); }