On this topic: My absolute favorite Common Lisp special operator is `(the`. Usage, `(the value-type form`, as in `(the integer (do-a-bunch-of-math))`.

At first glance, it looks like your strong-typing tool. And it can be. You can build a static analyzer that will match, as best it can, the type of the form to the value-type and throw errors if they don't match. It can also be a runtime check; the runtime is allowed to treat `the` as an assert and throw an error if there's a mismatch.

But what the spec actually says is that it's a special operator that does nothing but return the evaluation of the form if the form's value is of the right type and the behavior is undefined otherwise. So relative to, say, C++, it's a clean entrypoint for undefined behavior; it signals to a Lisp compiler or interpreter "Hey, the programmer allows you to do shenanigans here to make the code go faster. Throw away the runtime type identifier, re-represent the data in a faster bit-pattern, slam this value into functions without runtime checks, assume particular optimizations will succeed, paint it red to make it go fasta... Just, go nuts."