wxHaskell is a portable and native GUI library for Haskell, built on wxWidgets. It is often used by those wanting to develop a GUI with a functional language.
wxHaskell is a middle-level GUI library. Several experimental high-level GUI library approaches are implemented on top of wxHaskell:
In contrast, the high-level GUI libraries FG and Grapefruit are implemented on top of the middle-level Gtk2Hs, which is based on GTK2.
All of these high-level libraries are experimental, using advanced mathematical concepts in their approach (see arrows in functional programming).