Andres,
The code you've listed shows how to go from an already existing instance of class FiniteMap to an instance for the same class that adds a trie structure on top of the underlying finite map implementation. You have to add a "base instance" to the code so that it can work. For example, by importing Data.Map and adding an "instance FiniteMap Data.Map.Map Char" with the appropriate definitions.
Thank you. I added the following: instance FiniteMap Map Char where empty = M.empty look = M.lookup bind = M.insert
You'll also need to add extra type information to "empty" in your example expression so that GHC can know which instance you actually want.
Is the follwing what you mean?
look "bar" $ bind "bar" 1 $ (empty :: Trie (Map Char) String Int) Just 1
P.S. FiniteMap uses another finite map, Data.Map in this case. I wonder why we can call it bootstrapping... --Kazu