New autoloaded turn-on-haskell-unicode-input-method + documentation

...and also add `turn-on-haskell-unicode-input-method` to the list of
choices presented for the `haskell-mode-hook` variable in the
customization interface.

This addresses #13

NEWS

@@ -35,6 +35,7 @@ See also [[https://github.com/haskell/haskell-mode/compare/v13.06...v13.07][deta
     shifting to apply.
 
 - Add `haskell-unicode-input-method.el` to distribution
+  (enable with `turn-on-haskell-unicode-input-method`)
 
 - Fix all byte-compilation warnings
 

haskell-mode.el

@@ -447,7 +447,8 @@ CONFIGURING INDENTATION
                                     ,@(if (fboundp 'capitalized-words-mode)
                                           '(capitalized-words-mode))
                                     turn-on-haskell-simple-indent turn-on-haskell-doc-mode
-                                    turn-on-haskell-decl-scan imenu-add-menubar-index))
+                                    turn-on-haskell-decl-scan imenu-add-menubar-index
+                                    turn-on-haskell-unicode-input-method))
 
 (defvar eldoc-print-current-symbol-info-function)
 

haskell-mode.texi

@@ -110,16 +110,22 @@ TODO
 
 @cindex Unicode
 
-TODO:
-@itemize
-@item
-tell about the issues and benefits of using Unicode in source code.
-@item
-tell about @code{UnicodeSyntax} language extension and the unicode
-symbol providing packages on hackage
-@item
-tell about the haskell-unicode entry methods
-@end itemize
+See the Haskell Wiki's entry on @uref{http://www.haskell.org/haskellwiki/Unicode-symbols, Unicode Symbols} for general information about Unicode support in Haskell.
+
+As Emacs supports editing files containing Unicode out of the box, so does Haskell Mode. As an add-on, Haskell Mode includes the @code{haskell-unicode} input method which allows you to easily type a number of Unicode symbols that are useful when writing Haskell code; for more details @xref{Input Methods,,,Emacs}.
+
+To automatically enable the @code{haskell-unicode} input method in haskell-mode buffers use @kbd{M-x customize-variable @key{RET} haskell-mode-hook} or put the following code in your `.emacs` file:
+
+@example
+(add-hook 'haskell-mode-hook 'turn-on-haskell-unicode-input-method)
+@end example
+
+@noindent
+To temporarily enable this input method for a single buffer you can use @kbd{M-x turn-on-haskell-unicode-input-method}.
+
+When the @code{haskell-unicode} input method is active, you can simply type @samp{->} and it is immediately replaced with @samp{→}. Use @kbd{C-\} to toggle the input method. To see a table of all key sequences use @kbd{M-x describe-input-method @key{RET} haskell-unicode}. A sequence like @samp{<=} is ambiguous and can mean either @samp{⇐} or @samp{≤}. Typing it presents you with a choice. Type @kbd{1} or @kbd{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 by setting @code{input-method-highlight-flag} to @code{nil} via @kbd{M-x customize-variable}.
 
 @node Indentation, inferior-haskell-mode, Unicode, Top
 @chapter Indentation

haskell-unicode-input-method.el

@@ -37,6 +37,13 @@
 (provide 'haskell-unicode-input-method)
 (require 'quail)
 
+;;;###autoload
+(defun turn-on-haskell-unicode-input-method ()
+  "Set input method `haskell-unicode'.
+See Info node `Unicode(haskell-mode)' for more details."
+  (interactive)
+  (set-input-method "haskell-unicode"))
+
 (quail-define-package
  "haskell-unicode" ;; name
  "UTF-8"           ;; language