TeX is kind of an unfortunate accident in that respect: Knuth had explicitly set out to make a relatively underpowered macro processor, not a general-purpose pr

TeX is kind of an unfortunate accident in that respect: Knuth had explicitly set out to make a relatively underpowered macro processor, not a general-purpose programming language; yet at the end he couldn’t help realizing he had, in fact, built a Turing-complete language. (Some parts of appendix D of the TeXbook are much easier to comprehend if you know what continuation passing is.) When he did set out to build a programming language, Knuth built METAFONT, and it’s just ridiculous how much nicer that is to program—even though it shares with TeX its token-stream-transformer nature and the standard pitfalls of grammarless macroexpanders such as miserable syntax error messages.