I can think of a couple examples off the top of my head --- TeX and template metaprogramming. Although I think Knuth protests too much when he says that he tri

I can think of a couple examples off the top of my head --- TeX and template metaprogramming. Although I think Knuth protests too much when he says that he tried not to make TeX Turing complete. At any rate, in both cases, Turing-completeness should be considered a hazard. There should be a warning label on TeX, particularly: WARNING: TeX is Turing complete. Proceed with caution!