[Someone]

Blacklisting (checking that the input doesn’t contain any of a fixed set of known troublemakers) is asking for trouble, but whitelisting (checking that the input doesn’t contain anything but a fixed set of known safe constructs) should be fine.

If your whitelist allows a wide range of constructs, it isn’t much easier to check that an input is in the allowed set than to write an evaluator that is limited to that set, so it may not be much of an advantage to have a more powerful ”eval” lying around.