View cart if already in cart

function king_replace_loop_add_to_cart_button( $button, $product  ){

    // Not needed for variable products
    if( $product->is_type( 'variable' ) )
        return $button;

    if ( is_shop() && $product->is_purchasable() && $product->is_in_stock() ){

        // Button text here
        $button_text = __( "View product", "woocommerce" );

        return '<a class="button" href="' . $product->get_permalink() . '">' . $button_text . '</a>';
    }
}

add_filter( 'woocommerce_loop_add_to_cart_link', 'king_replace_loop_add_to_cart_button', 10, 2 );