I've also written a few wrappers for Haskell libraries over at http://darcsden.com/alex - see http, json, and command.

Basically, you define your methods in Haskell, and call them from Atomo; these methods can be defined as an expression (=:::), a value (=::), or some arbitrary VM action to be executed to yield a value (=:). (Admittedly those operators have gotten a bit silly.)

The definitions use QuasiQuotes for the method pattern, and can use them for expressions as well, though that's not encouraged (operator precedence and macros make it a tricky thing to do at compile time). They look a bit noisy - [$p|x foo: y|] but that'll be fixed come GHC 7, where that pesky $ is removed.