I have created an SDK for Stellar in Haskell. Since security is essential in applications such as Stellar, Haskell's strong type system is very useful to prevent costly bugs. Currently, the SDK support querying the Stellar network through a Horizon server. Furthermore, it allows you to create new keypairs and to build, sign and submit transactions.
The sources are available on Github: https://github.com/teequoo/haskell-stellar-sdk
There are several aspects that still require some work. I plan to add support for streaming data from Horizon, using the conduit package. Furthermore, I want to add comprehensive documentation and tests.
If you have questions or feedback, please let me know.