fix issues related to export & function (#2002)

- `unused` function names
- confusion with function call syntax

fixes #2001

lib/parse.js

@@ -2417,11 +2417,16 @@ function parse($TEXT, options) {
             }
         }
 
-        var is_definition = is("keyword", "var") || is("keyword", "let") || is("keyword", "const");
+        var is_definition = is("keyword", "var")
+            || is("keyword", "let")
+            || is("keyword", "const")
+            || is("keyword", "function") && !is_default;
         if (is_definition) {
             exported_definition = statement();
+        } else if (is("keyword", "function")) {
+            exported_value = expr_atom(false);
         } else {
-            exported_value = expression();
+            exported_value = expression(false);
             semicolon();
         }