HERA is an implementation of exact real arithmetic in Haskell using the approach by Andrej Bauer and Iztok Kavkler, see these and these slides. It uses the fast multiple precision floating point library MPFR. Download source, and see documentation and examples of usage at my home page.
[Note by Andrej: this is a guest post by AleÅ¡ Bizjak, a first-year student of mathematics at my department. I am very proud of the excellent work he did on his summer project.]