Quoting Jan Brosius (jan.brosius@skynet.be):
If there is a Gtkairo backend for mcclim than I would expect that mcclim uses an ffi e.g. cffi. If so I would like to have some working knowledge of how it is done and what C library one uses. I mean wxcl uses wxWidgets (written in C++), swig to "translate it to cffi and also cffi. But I couldn't find a folder like cffi in the mcclim distribution.
Gtkairo uses CFFI to call GTK+ functions. The FFI definitions for that are partly hard-written (gtk-ffi.lisp, cairo-ffi.lisp), partly auto-generated (ffi.lisp), and can be found in mcclim/Backends/gtkairo/. Users are not meant to call those FFI functions directly, and only a small part of GTK+ functionality is used. If you are looking for complete GTK+ bindings, consider CLG or one of all the other GTK+ bindings available for Common Lisp. d.