In two recent posts here, I've suggested moderately evil things to do with the C preprocessor, both on the same theme of defining a macro that can be used like a loop keyword by following its invocation with a statement or block of your choice.

Last week some further thoughts on the subject occurred to me, which were rather more comprehensive and also considerably more evil still. I think I've now taken that general idea to somewhere near the limit of its possibilities, by developing a general system of construction-kit macros that make it more or less feasible for people to develop custom loop types.

The result is far too long to fit in this post, so I've put it up on my website. For those with a strong stomach and an interest in metaprogramming or C abuse or both, I present ‘Metaprogramming Custom Control Structures in C’: http://www.chiark.greenend.org.uk/~sgtatham/mp/.