whoops, lost the bad-word error case

eval.go

@@ -87,6 +87,8 @@ func (c *Context) Exec(w Word) error {
 		if err != nil {
 			return err
 		}
+	} else {
+		return fmt.Errorf("unable to parse word %s", w.Name)
 	}
 	return nil
 }