| This seems to be a lot of mechanism for questionable benefit. A simpler and cleaner | approach, IMHO, is the following: I rather agree. One other idea though. Suppose you say class ComplicatedClass x where _simpleTitleFn :: x -> String muchMoreComplicatedTitleFn :: extra arguments -> x -> IO ... In general GHC doesn't report "warning unused" for variables whose name begin with an underscore. In the case of class methods, I don't think it suppresses the warning, but that would be an easy change to make. Indeed, it would arguably be more consistent to do so anyway
#-}) which compiles exactly as normal except that (1) no warning is given for instances which don't define it; (2) a warning is given whenever anyone outside the class declaration *uses* simpleTitleFn.
The "_" idea would achieve (1). You could get (2) by not exporting the "_" method from the module defining ComplicatedClasss. How would that be? Simon