Simple JS implementation of Prismatic's blog post about Graph

dumb_graph.js

function sum (fn, xs) {
  var toRet = 0;
  for (var i = 0, ii = xs.length; i < ii; i++) {
    toRet += fn(xs[i], i, xs);
  }
  return toRet;
}

function update(t, o) {
  for (var k in o) {
    t[k] = o[k];
  }
  return t;
}

function depGraph(graph) {
  var deps = {};
  for (var k in statsGraph) {
    var fnStr = graph[k].toString();
    var fnArgs = fnStr.slice(fnStr.indexOf('(')+1, fnStr.indexOf(')')).split(/\s*,\s*/);
    deps[k] = fnArgs;
  }
  return deps;
}

function satisfyDeps(depsList, results) {
  var acc = [];
  for (var i = 0, ii = depsList.length; i < ii; i++) {
    if (typeof results[depsList[i]] == 'undefined') {
      return false;
    } else {
      acc.push(results[depsList[i]]);
    }
  }
  return acc;
}

function eagerCompile(graph) {
  return function(startValue) {
    var deps = depGraph(graph);
    var k = Object.keys(deps);
    var res = update({}, startValue);
    var processing, args, missingDep = true;
    do {
      processing = false;
      for (var i = 0, ii = k.length; i < ii; i++) {
        if (typeof res[k[i]] == 'undefined') {
          if (args = satisfyDeps(deps[k[i]], res)) {
            res[k[i]] = graph[k[i]].apply(res, args);
            processed = true;
            missingDep = false
          }
        }
      }
      if (missingDep) {
        throw 'Missing dependency';
      }
    } while (processing);

    return res;
  }
}

var statsGraph = {
  n:  function(xs)    { return xs.length; },
  m:  function(xs, n) { return sum(function(x){ return x;     }, xs) / n; },
  m2: function(xs, n) { return sum(function(x){ return x * x; }, xs) / n; },
  v:  function(m, m2) { return m2 - (m * m); }
};

var stats = eagerCompile(statsGraph);

console.log(stats({xs: [1, 2, 3, 6]}));