Your comments betray a lot of ignorance, so I will just point out the glaring inaccuracies in #1. Here are two different expression parsers that are likely ins

Your comments betray a lot of ignorance, so I will just point out the glaring inaccuracies in #1. Here are two different expression parsers that are likely installed on machines you use, and they absolutely make a function call for each level of precedence (eval1, eval2, ..., exp1, exp2, ...) http://code.metager.de/source/xref/gnu/coreutils/src/expr.c http://code.metager.de/source/xref/gnu/coreutils/src/expr.c https://opensource.apple.com/source/bash/bash-76.1/bash/expr.c https://opensource.apple.com/source/bash/bash-76.1/bash/expr... My point is not that this is BAD -- it probably doesn't matter on modern machines. I'm just saying there are choices to make. Parsing requires some knowledge and choices -- that's all. You don't just "type out the code". #3 is not a refutation, because all the languages I mentioned are extraordinarily common. The answer to "parsing real languages is hard" is not "don't parse real languages". I can also tell by #4 that you don't have any background in security. It's not about YOUR code per se. It's about code that is deployed and that we all rely on.