[brudgers]

My understanding is that typically, Lisp macros are expanded at 'compile' time. The compiler expands macros recursively until there's nothing left to expand and then compilation proceeds normally.

A Lisp macro operates on data structures. Macros transform one data structure into another data structure. Lisp code is a data structure (typically a list) and ultimately all macros get resolved by expansion to ordinary Lisp code and the expanded code then is compiled/interpreted.

Unlike C, Lisp macros have access to all of Lisp (including other macros) during expansion. So a macro's expansion can be determined programmatically by executing Lisp code...this part is where it gets harder to understand macros intuitively because the code called during the macro expansion phase does not have access to the code that runs at the runtime and vice versa.

That's why it is handy to think about macros as manipulating data structures...we don't expect data structures to return values or generate values in the environment by execution.