[Go][excerpt] list filter.

// Excerpt
// Select items from the list when item fulfill the predicate.
// Implement grep function object to use this method.
func (list *List) Select(grep func(interface{}) (bool, error)) (*List, error) {
    newList := New()

    current := list.head
    for current != nil {
        b, err := grep(current.data)
        if err != nil {
            return newList, err
        }

        if b == true {
            newList.Push(current.data)
        }

        current = current.next
    }

    return newList, nil
}