Return block of files, all dirs first (See related posts)

    dir-file-sort: func [
        {Returns the block of files with directories first, followed by
        files, with each group sorted.}
        block [any-block!]
        /local result
    ][
        result: copy []
        foreach blk lib/ser/split block [:dir?] none [
            append result sort blk
        ]
    ]