But in the SLIME debugger I'm unable to locate those 1 2 3 4 5 which
were pushed on the stack (and there is no function to try to query the
argument list from, since it's an unexisting function, its frame was
Sorry, I was confused by your needs. There is no notion of arguments in the debugger information. The only notion rigth now is that of lexically and globally bound variables. Thus, the only exposed "values" are those assigned to variables. Since your function is not defined, when the error handler is invoked, those values are not assigned to any variable and cannot be inspected by the debugger.
The only possible fix I see for this is to add some convenience functions to peek the interpreter stack. This can easily be done, adding a few more commands to the debugger and using the C interface to get those values. The basic tool is ECL_STACK_REF(env,relative_index), a C macro that accesses the interpreter stack. With this macro and a small c-inline code, one can inspect the unassigned values