Error while implementing the contract in existing class: Laravel 5.2.31

I am following this link to implement it

I did below steps to implement the Contract in my existing class.

Below is the class where I will write some logic also before sending it to controller

class RoleBL implements IRole {

    public function All() {
        return (new RoleDb())->All();
    }

}

Database Function

class RoleDb {
    public function All() {
        $Roles = \App\Models\Role\RoleModel
                ::all();
        return $Roles;
    }
}

Interface

interface IRole {
    public function All();
}

Service Provider class

class RoleServiceProvider extends \Illuminate\Support\ServiceProvider {

    public function register()
    {
        $this->app->bind('App\Contract\Role\IRole', function($app){
            return new \App\Classes\BusinessLogic\Role\RoleBL($app['HttpClient']);
        });
    }
}

Controller - Constructor

public function __construct(\App\Classes\Role\IRole $_roles) {
    parent::__construct();
    $roles = $_roles;
}

When I ran the site, I got following error.

Target [App\Contract\Role\IRole] is not instantiable while building [App\Http\Controllers\Website\Membership\MembershipController].

Please guide me if I missed anything?

via Chebli Mohamed