LispWorks User Guide and Reference Manual > 6 The Advice
Facility > 6.2 Combining the advice   6.2.1 :before and :after
advice  First we deal with the case when there is no around
advice present. Here each of the pieces of before advice are
called in turn, with the same arguments that were given to the
function, next the original definition is called with these
arguments, and finally each of the pieces of after advice is
called in reverse order with the same arguments (so that by
default the most recently added piece of after advice is invoked
last). The results returned by the function call are the values
produced by the last piece of after advice to be called (if
there is one), or by the original definition (if there is no
after advice).  Note that none of these bits of code should
destructively modify the arguments that they receive. Adding a
piece of before advice thus provides a simple way of specifying
some additional action to be performed before the original
definition, and before any older bits of be