Strange behavior in Laravel

this open the view page with tons of errors (can't read the front-end=css/js codes)

Route::get('category/{cat}' , function($cat) {
   return view('main/category');
});

however this opens it without any problem

Route::get('category' , function() {
   return view('main/category');
});

how to implement this route parameters ?

via Chebli Mohamed