This package provides haskell-unicode-input-method, an input method which allows you to easily type a number of Unicode symbols that are useful when writing Haskell code.
To automically load in haskell-mode put the following code in your .emacs file:
(require 'haskell-unicode-input-method)
(add-hook 'haskell-mode-hook
(lambda () (set-input-method "haskell-unicode")))
Make sure the directory containing the .el file is in your load-path, for example:
(add-to-list 'load-path "~/.elisp/emacs-haskell-unicode-input-method")
To manually enable use M-x set-input-method or C-x RET C-\ with haskell-unicode. Note that the elisp file must be evaluated for this to work.
Now you can simply type -> and it is immediately replaced with
→. Use C-\ to toggle the input method. To see a table of all
key sequences use M-x describe-input-method haskell-unicode. A
sequence like <= is ambiguous and can mean either ⇐ or ≤. Typing
it presents you with a choice. Type 1 or 2 to select an option or keep
typing to use the default option.
If you don't like the highlighting of partially matching tokens you can turn it off:
(setq input-method-highlight-flag nil)