TeX is weird. Really weird, if one expects it to work like a modern programming language. The crux of it is that it's a macro-expansion language, which means t

TeX is weird. Really weird, if one expects it to work like a modern programming language. The crux of it is that it's a macro-expansion language, which means that you pretty much need to do the kind of stream-processing approach TeX uses, since you don't know the expansion of a macro up-front, which in turn can very well change the meaning of tokens downstream of that again. For an (admittedly extreme) example of this, consider TikZ; it's basically an entire new programming language, implemented purely by TeX macros. I sometimes compare it to programming in Common Lisp, but you all you have available are the primitives (except lambda, I supppose) and defmacro.