Step2.cs

var linkOptions = new DataflowLinkOptions { PropagateCompletion = true };

// RECURSION: If the entry is a directory, feed it back into the same block.
getFolderContents.LinkTo(getFolderContents, linkOptions,
    entry => Directory.Exists(entry));

// BASE CASE: If the entry is a file, send it forward for hashing.
getFolderContents.LinkTo(computeMD5, linkOptions,
    entry => File.Exists(entry));

// Final stage: display the hash.
computeMD5.LinkTo(displayResult, linkOptions);