Haskell-Conceal is a project mainly written in Vim Script, it's free.
Add some conceal operation to haskell's syntax
This is a mirror of http://www.vim.org/scripts/script.php?script_id=3200
Use Vim 7.3 Conceal feature to display unicode operator in Haskell without changing the underlying file.
GitHub: https://github.com/Twinside/vim-haskellConceal