There are currently a number of different ways to generate tags with Haskell.
This page should be used to collect information on them, including information on how to use tags with common editors and what benefits they can give you.
Haskell tag generators
Chris Ryder and Simon Thompson give a tag generator's source in a paper
echo ":ctags" | ghci -v0 Main.hs
echo ":etags" | ghci -v0 Main.hs
utils/hasktags from GHC.
Random other bits
vim :help tags-file-format :help cursorhold-example