Add a convenience 'Prelude' module when using indexed do notation.

This is less error prone and way easier than all clients having to
redefine the necessary operators. It's also less code alltogether.

Signed-off-by: Austin Seipp <mad.one@gmail.com>
Add tree walking example.

Signed-off-by: Austin Seipp <mad.one@gmail.com>
Commented out copy of the 'reverse' shift operators

Signed-off-by: Austin Seipp <mad.one@gmail.com>
Update tutorial regarding the use of RankNTypes.

Signed-off-by: Austin Seipp <mad.one@gmail.com>
Fix re-export of Prelude in indexed prelude

Signed-off-by: Austin Seipp <mad.one@gmail.com>
Wibbles.

Signed-off-by: Austin Seipp <mad.one@gmail.com>