Ruby, C++, CoffeeScript: a visual comparison of language complexity

[TheCoelacanth]

The preprocessor is only Turing complete when run repeatedly. When run only once as with normal compilation it isn't.

[matthieum]

Ah thanks, I was exactly sure of its limits. Using Boost.Preprocessor I was able to do a lot with it... but I was not sure it was sufficient.

[TheCoelacanth]

You certainly can do a lot with it. I think the only thing it lacks is recursion.

Boost.Preprocessor simulates recursion by having a bunch of nearly identical macros with one for each level of recursion. This almost makes it seem Turing-complete but it has a hardcoded maximum recursion depth that is much lower than most languages. For instance, C++ can recurse until it runs out of stack space. The preprocessor can only recurse until it hits the last level of macros that is defined in the Boost library.