Currently, HFM supports importing of .hs files. This feature creates a new file inside the .hsproj with the same file name and contents as the original file.
However, there are cases when the user is working on a repo of .hs files. In this case, it makes sense to be able to apply the modifications done within HFM back to the repo. Unfortunately, there seems to be no way to "sync" back your modifications except by manually copying the changes in the source code.
The current strategy for source control with HFM is mentioned here: http://community.hfm.io/hc/en-us/articles/213724557-How-do-I-use-Git-with-Haskell-for-Mac-
However, my suggestion is that aside from import, add support allowing HFM to read/write to an external file. This should look like a symlink inside .hsproj.
In doing so, the user can have a separate repo of .hs files without the need to check-in/commit the .hsproj itself.