MochΛ is a Haskell to Objective-C language binding for Mac OS X. Using Mocha, Haskell code can send messages to Objective-C objects, and Objective-C class declarations can be written in Haskell. Haskell API definitions are provided for the entire Mac OS X Cocoa framework, and automated interface generation can be performed for any user-supplied frameworks.

Update: Mocha has been officially discontinued—but never fear, Wolfgang Thaller and I have been working on HOC, which fulfils much of the same goals that Mocha strived for, and furthermore, it’s actually released and working! See the HOC release announcement for more details.