Connecting to mongohq with Haskell is really simple.

1. Create yout account at https://mongohq.com

2. Install mongodb via cabal:

cabal install mongodb

3. Check this code:

This connects, logs in, inserts and then retrieves a document in a collection. Runnin' main will print something like this:
[[(Chunk "_id" Empty,BsonObjectId 23543969989857644967178010624),(Chunk "author" Empty,BsonString (Chunk "Jo\195\163o Milho" Empty)),(Chunk "text" Empty,BsonString (Chunk "Hello MongoHQ World!" Empty))]]

Your document will also be visible in the mongohq page.

4. More info here: http://github.com/srp/mongoDB/

Enjoy!