add stream folder with scan and scan-merge

stream/scan-merge.js

@@ -0,0 +1,26 @@
+//! adapted for mithril from flyd https://github.com/paldepind/flyd
+'use strict'
+
+var combine = require('../stream').combine
+
+module.exports = function (tuples, seed) {
+  var streams = tuples.map(function (tuple) {
+		var stream = tuple[0]
+		if (stream._state.state === 0) stream(undefined)
+    return stream
+  })
+
+  var newStream = combine(function () {
+    var changed = arguments[arguments.length - 1]
+
+    streams.forEach(function (stream, idx) {
+      if (changed.indexOf(stream) > -1) {
+        seed = tuples[idx][1](seed, stream._state.value)
+      }
+    })
+
+    return seed
+  }, streams)
+
+  return newStream
+}