perf(scan): add performance benchmark for fold

perf/scan.js

@@ -0,0 +1,81 @@
+var Benchmark = require('benchmark');
+var xs = require('../lib/index').default;
+var most = require('most');
+var rx = require('rx');
+var rxjs = require('@reactivex/rxjs');
+var kefir = require('kefir');
+var bacon = require('baconjs');
+var lodash = require('lodash');
+var highland = require('highland');
+
+var runners = require('./runners');
+var kefirFromArray = runners.kefirFromArray;
+
+// Create a stream from an Array of n integers
+// filter out odds, map remaining evens by adding 1, then reduce by summing
+var n = runners.getIntArg(1000000);
+var a = new Array(n);
+for(var i = 0; i< a.length; ++i) {
+  a[i] = i;
+}
+
+var suite = Benchmark.Suite('scan -> reduce ' + n + ' integers');
+var options = {
+  defer: true,
+  onError: function(e) {
+    e.currentTarget.failure = e.error;
+  }
+};
+
+suite
+  .add('xstream', function(deferred) {
+    runners.runXStream(deferred, xs.from(a).fold(sum, 0).fold(passthrough, 0).last());
+  }, options)
+  .add('most', function(deferred) {
+    runners.runMost(deferred, most.from(a).scan(sum, 0).reduce(passthrough, 0));
+  }, options)
+  .add('rx 4', function(deferred) {
+    runners.runRx(deferred, rx.Observable.fromArray(a).scan(sum, 0).reduce(passthrough, 0));
+  }, options)
+  .add('rx 5', function(deferred) {
+    runners.runRx5(deferred, rxjs.Observable.fromArray(a).scan(sum, 0).reduce(passthrough, 0));
+  }, options)
+  .add('kefir', function(deferred) {
+    runners.runKefir(deferred, kefirFromArray(a).scan(sum, 0).scan(passthrough, 0).last());
+  }, options)
+  .add('bacon', function(deferred) {
+    runners.runBacon(deferred, bacon.fromArray(a).scan(0, sum).reduce(0, passthrough));
+  }, options)
+  .add('highland', function(deferred) {
+    runners.runHighland(deferred, highland(a).scan(0, sum).reduce(0, passthrough));
+  }, options)
+  .add('lodash', function() {
+    return lodashScan(sum, 0, a).reduce(passthrough, 0);
+  })
+  .add('Array', function() {
+    return arrayScan(sum, 0, a).reduce(passthrough, 0);
+  });
+
+runners.runSuite(suite);
+
+function arrayScan(f, initial, a) {
+  var result = initial;
+  return a.map(function(x) {
+    return result = f(result, x);
+  });
+}
+
+function lodashScan(f, initial, a) {
+  var result = initial;
+  return lodash(a).map(function(x) {
+    return result = f(result, x);
+  });
+}
+
+function sum(x, y) {
+  return x + y;
+}
+
+function passthrough(z, x) {
+  return x;
+}