Experimental async lambda implementation.

lib/mu/renderer.js

@@ -50,12 +50,26 @@ function _render(tokens, context, partials, stream, callback) {
       case 'mustache':    
         switch (token[1]) {
         case 'utag': // Unescaped Tag
-          stream.emit('data', s(normalize(context, token[2])));
-          return next();
+          var v = normalize(context, token[2], undefined, function( v ) {
+            stream.emit('data', s(v));
+            next();
+          });
+          if( v !== undefined ) {
+            stream.emit('data', v );
+            next();
+          }
+          return;
 
         case 'etag': // Escaped Tag
-          stream.emit('data', escape(s(normalize(context, token[2]))));
-          return next();
+          var v = normalize(context, token[2], undefined, function( v ) {
+            stream.emit('data', escape(s(v)));
+            next();
+          });
+          if( v !== undefined ) {
+              stream.emit('data', escape(v));
+              next();
+          }
+          return;
 
         case 'section':
           var res = normalize(context, token[2], token[3]);
@@ -106,11 +120,15 @@ function escape(string) {
   return string.replace(/[&<>"]/g, escapeReplace);
 }
 
-function normalize(context, name, body) {
+function normalize(context, name, body, next) {
   var val = walkToFind(context, name);
 
   if (typeof(val) === 'function') {
-    val = val.call(smashContext(context), body);
+    var fn = val;
+    val = fn.call(smashContext(context), body, next);
+    if( val === undefined && fn.length < 2 ) { // => val doesn't accept a callback function
+      val = '';
+    }
   }
 
   return val;