ghc-tags-core library provides:
a function to extract tag information from HsModule GhcPs parsed tree representation of Haskell code
parsers ctag and etag style tag files (vim / emacs)
formatting tags into ctag and etag files.
tries to be compatible with universal-ctags
Check out these projects:
ghc-tags-plugin -
a ghc compiler
plugin
which extracts tags during GHC's parser pass
more to come!