Yi (editor)
Yi is a text editor written and extensible in Haskell. The goal of Yi is to provide a flexible, powerful and correct editor core dynamically scriptable in Haskell.
Yi used to be a Haskell interpreter, very much like Emacs is an Emacs Lisp interpreter; however, the current version of Yi recompiles the code that describes its settings (including editing modes and extensions). Specifically, Yi is implemented as a small executable program which compiles through GHC the larger body of code which actually constitutes a useful editor; this small 'kernel' can repeatedly recompile (and thus type-check) the extensions. This makes it easy to dynamically hack, experiment and modify Yi despite it being written in a strongly statically typed language. Using Haskell as a first-class extension language means that other libraries and tools written in Haskell are also readily usable in editor code.
The long term goal of the project is to in essence make Yi the editor of choice for Haskell hackers in much the same way that Emacs is the editor of choice for Lisp programmers.
Read more about Yi (editor): Front Ends, "Emulation Modes"