In theory there should be no difference between theory and practice, but in practice there often is. TeX's syntax itself being Turing-complete means you can bar

In theory there should be no difference between theory and practice, but in practice there often is. TeX's syntax itself being Turing-complete means you can barely start to do static analysis on the code before hitting a wall you can only get over by installing a huge fraction of the ~1GB download that is TeXLive. "Being theoretically possible" is in no way orthogonal to "impractical in many or most circumstances".