open System.IO
module seqModule =
    let private canExecuteFunc(func) =
        fun e ->
            try
                func(e) |> ignore
                true
            with
                | _ -> false
    let private getFileList = fun (di:DirectoryInfo) -> di.GetFiles()
    let private openFileForRead = fun (fi:FileInfo) -> let fs = fi.OpenRead()
                                                       fs.Close()

    let rec private getSubFolders(dirInfo:DirectoryInfo) =
            let dirLst = dirInfo.GetDirectories() |> Array.filter (canExecuteFunc(getFileList)) |> Seq.ofArray
            match Seq.isEmpty dirLst with
                | true  -> seq { yield! Seq.empty }
                | false -> seq { yield! dirLst
                                 yield! Seq.map getSubFolders dirLst
                                       |> Seq.concat }

    let getFolders(path) =
        let di = new DirectoryInfo(path)
        seq { yield di
              yield! getSubFolders(di) }

    let getAllFiles(path) =
        let getFiles = fun (di:DirectoryInfo) -> di.GetFiles() |> Seq.ofArray |> Seq.filter (canExecuteFunc(openFileForRead))
        getFolders(path)
        |> Seq.map getFiles
        |> Seq.concat