diff --git a/jmespath.js b/jmespath.js
index f59e8e4..61a815f 100644
--- a/jmespath.js
+++ b/jmespath.js
@@ -17,6 +17,13 @@
     }
   }
 
+  function isTraversable(obj) {
+    if (obj == null) return false;
+    var type = typeof obj;
+    if (type != 'function' && type != 'object') return false;
+    return true;
+  }
+
   function strictDeepEqual(first, second) {
     // Check the scalar case first.
     if (first === second) {
@@ -402,6 +409,10 @@
               if (stream[this._current] === "=") {
                   this._current++;
                   return {type: TOK_EQ, value: "==", start: start};
+              } else {
+                var error = new Error("Unexpected token: do you mean `==' operator ?");
+                error.name = "ParserError";
+                throw error;
               }
           }
       },
@@ -868,7 +879,7 @@
             case "Field":
               if (value === null ) {
                   return null;
-              } else if (isObject(value)) {
+              } else if (isTraversable(value)) {
                   field = value[node.name];
                   if (field === undefined) {
                       return null;
@@ -1660,6 +1671,14 @@
       return interpreter.search(node, data);
   }
 
+  function exec(ast, data) {
+      var runtime = new Runtime();
+      var interpreter = new TreeInterpreter(runtime);
+      runtime._interpreter = interpreter;
+      return interpreter.visit(ast, data);
+  }
+
+  exports.exec = exec;
   exports.tokenize = tokenize;
   exports.compile = compile;
   exports.search = search;