If a macroexpansion communicates with other parts of the system using eg. structures or instances, expanding nested macros doesn't work in Slime: ...assuming you have CFFI installed and loaded... (cffi:defcallback foo :void ((data :string)) (error data)) C-RET expands it to (PROGN (CFFI-SYS:%DEFCALLBACK FOO :VOID (DATA) (:POINTER) (LET ((DATA (CFFI:TRANSLATE-FROM-FOREIGN DATA #<CFFI::FOREIGN-STRING-TYPE :UTF-8>))) (BLOCK FOO (ERROR DATA))) :CALLING-CONVENTION :CDECL) 'FOO) where the %DEFCALLBACK is also a macro. Trying to re-expand that using C-RET breaks when it tries to READ #<. It would be nice if (a) the second expansion worked (2) the #<...> objects in the buffer were presentations. Cheers, -- Nikodemus