macroexpand-1

(macroexpand-1 form)

Expands form once when its operator is a user macro (defined with defmacro) or a built-in macro, and returns the form unchanged otherwise. Only the top-level operator is expanded; subforms are left alone.

The second value is Common Lisp's expanded-p flag: (multiple-value-list (macroexpand-1 '(unless c x))) is ((IF C NIL X) T). The environment argument is accepted and ignored (there is no lexical macro environment to consult).

On the compilation path only a LITERAL quoted argument expands: the CLI folds the call to its expansion at compile time. A computed argument reaches a compiled program, which has no macro table left, so it answers the form unchanged with expanded-p nil — unless the form IS a macro call, which signals macroexpand-1: a compiled program cannot expand a macro at run time. That is the same answer macro-function's stub gives there, and it is what makes the usual "expand until it stops expanding" loop terminate on every backend.

A non-macro form is returned as-is: