special-operator-p

(special-operator-p symbol)

True when the symbol names one of the 25 ANSI special operators -- block, catch, eval-when, flet, function, go, if, labels, let, let*, load-time-value, locally, macrolet, multiple-value-call, multiple-value-prog1, progn, progv, quote, return-from, setq, symbol-macrolet, tagbody, the, throw, unwind-protect -- and nil for everything else.

nil includes the Common Lisp MACROS that rontolisp happens to implement as special forms of its own (defun, handler-case, dolist, ...). The question a caller asks is "may I apply this name", and those names answer it through macro-function instead, exactly as in Common Lisp.

Lite: a non-symbol argument answers nil where Common Lisp signals a type error.