Haskell library to "union mount" a bunch of folders onto an in-memory data structure, and keeping the latter in sync as the files change over time. Used in Ema and Emanote.
Both the mount and unionMount functions return a tuple value of type Dynamic, giving direct access to the initial value as well as the updater function that may be run in a separate thread. See how Ema uses it for an illustration.
See this example illustrating mounting a directory of Markdown files into (effectively) a Map FilePath String. A more involved example from Emanote demonstrates the "union" aspect of the library.