<s>
In	O
aspect	B-Architecture
and	O
functional	B-Language
programming	I-Language
,	O
advice	O
describes	O
a	O
class	O
of	O
functions	O
which	O
modify	O
other	O
functions	O
when	O
the	O
latter	O
are	O
run	O
;	O
it	O
is	O
a	O
certain	O
function	O
,	O
method	O
or	O
procedure	O
that	O
is	O
to	O
be	O
applied	O
at	O
a	O
given	O
join	B-Application
point	I-Application
of	O
a	O
program	O
.	O
</s>
<s>
The	O
Emacspeak	B-Language
Emacs-addon	O
makes	O
extensive	O
use	O
of	O
advice	O
:	O
it	O
must	O
modify	O
thousands	O
of	O
existing	O
Emacs	B-Application
modules	O
and	O
functions	O
such	O
that	O
it	O
can	O
produce	O
audio	O
output	O
for	O
the	O
blind	O
corresponding	O
to	O
the	O
visual	O
presentation	O
,	O
but	O
it	O
would	O
be	O
infeasible	O
to	O
copy	O
all	O
of	O
them	O
and	O
redefine	O
them	O
to	O
produce	O
audio	O
output	O
in	O
addition	O
to	O
their	O
normal	O
outputs	O
;	O
so	O
,	O
the	O
Emacspeak	B-Language
programmers	O
define	O
advice	O
functions	O
which	O
run	O
before	O
and	O
after	O
.	O
</s>
<s>
Another	O
Emacs	B-Application
example	O
;	O
suppose	O
after	O
one	O
corrected	O
a	O
misspelled	O
word	O
through	O
ispell	B-Application
,	O
one	O
wanted	O
to	O
re-spellcheck	O
the	O
entire	O
buffer	O
.	O
</s>
<s>
ispell-word	O
offers	O
no	O
such	O
functionality	O
,	O
even	O
if	O
the	O
spellchecked	O
word	O
is	O
used	O
a	O
thousand	O
times	O
.	O
</s>
<s>
One	O
could	O
track	O
down	O
the	O
definition	O
of	O
ispell-word	O
,	O
copy	O
it	O
into	O
one	O
's	O
Emacs	B-Application
,	O
and	O
write	O
the	O
additional	O
functionality	O
,	O
but	O
this	O
is	O
tedious	O
,	O
prone	O
to	O
broken-ness	O
(	O
the	O
Emacs	B-Application
version	O
will	O
get	O
out	O
of	O
sync	O
with	O
the	O
actual	O
Ispell	B-Application
Elisp	O
module	O
,	O
if	O
it	O
even	O
works	O
out	O
of	O
its	O
home	O
)	O
.	O
</s>
<s>
What	O
one	O
wants	O
is	O
fairly	O
simple	O
:	O
just	O
to	O
run	O
another	O
command	O
after	O
ispell-word	O
runs	O
.	O
</s>
<s>
However	O
,	O
these	O
were	O
dropped	O
from	O
C++	B-Language
.	O
</s>
<s>
Advices	O
are	O
part	O
of	O
the	O
Common	B-Application
Lisp	I-Application
Object	I-Application
System	I-Application
(	O
CLOS	B-Application
)	O
,	O
as	O
:before	O
,	O
:after	O
,	O
and	O
:around	O
methods	O
,	O
which	O
are	O
combined	O
with	O
the	O
primary	O
method	O
under	O
"	O
standard	O
method	O
combination	O
"	O
.	O
</s>
<s>
Common	O
Lisp	B-Language
implementations	O
provide	O
advice	O
functionality	O
(	O
in	O
addition	O
to	O
the	O
standard	O
method	O
combination	O
for	O
CLOS	B-Application
)	O
as	O
extensions	O
.	O
</s>
<s>
LispWorks	O
supports	O
advising	O
functions	O
,	O
macros	O
and	O
CLOS	B-Application
methods	O
.	O
</s>
<s>
"	O
Advising	O
"	O
found	O
its	O
way	O
into	O
BBN	B-Language
Lisp	I-Language
and	O
later	O
into	O
Xerox	O
PARC	O
's	O
Interlisp	B-Language
.	O
</s>
<s>
It	O
also	O
found	O
its	O
way	O
to	O
Flavors	B-Language
,	O
the	O
first	O
object-oriented	B-Language
extension	O
to	O
Lisp	B-Language
developed	O
at	O
MIT	O
.	O
</s>
