<s>
A	O
class	B-Application
browser	I-Application
is	O
a	O
feature	O
of	O
an	O
integrated	B-Application
development	I-Application
environment	I-Application
(	O
IDE	B-Application
)	O
that	O
allows	O
the	O
programmer	O
to	O
browse	O
,	O
navigate	O
,	O
or	O
visualize	O
the	O
structure	O
of	O
object-oriented	B-Language
programming	I-Language
code	O
.	O
</s>
<s>
Most	O
modern	O
class	B-Application
browsers	I-Application
owe	O
their	O
origins	O
to	O
Smalltalk	B-Application
,	O
one	O
of	O
the	O
earliest	O
object-oriented	B-Language
languages	I-Language
and	O
development	O
environments	O
.	O
</s>
<s>
The	O
typical	O
Smalltalk	B-Application
"	O
five-pane	O
"	O
browser	O
is	O
a	O
series	O
of	O
horizontally-abutting	O
selection	O
panes	O
positioned	O
above	O
an	O
editing	O
pane	O
,	O
the	O
selection	O
panes	O
allow	O
the	O
user	O
to	O
specify	O
first	O
a	O
category	O
and	O
then	O
a	O
class	O
,	O
and	O
further	O
to	O
refine	O
the	O
selection	O
to	O
indicate	O
a	O
specific	O
class	O
-	O
or	O
instance-method	O
the	O
implementation	O
of	O
which	O
is	O
presented	O
in	O
the	O
editing	O
pane	O
for	O
inspection	O
or	O
modification	O
.	O
</s>
<s>
Most	O
succeeding	O
object-oriented	B-Language
languages	I-Language
differed	O
from	O
Smalltalk	B-Application
in	O
that	O
they	O
were	O
compiled	B-Language
and	O
executed	O
in	O
a	O
discrete	O
runtime	B-Device
environment	I-Device
,	O
rather	O
than	O
being	O
dynamically	O
integrated	O
into	O
a	O
monolithic	O
system	O
like	O
the	O
early	O
Smalltalk	B-Application
environments	O
.	O
</s>
<s>
With	O
the	O
popularity	O
of	O
C++	B-Language
starting	O
in	O
the	O
late-1980s	O
,	O
modern	O
IDEs	O
added	O
class	B-Application
browsers	I-Application
,	O
at	O
first	O
to	O
simply	O
navigate	O
class	O
hierarchies	O
,	O
and	O
later	O
to	O
aid	O
in	O
the	O
creation	O
of	O
new	O
classes	O
.	O
</s>
<s>
With	O
the	O
introduction	O
of	O
Java	B-Language
in	O
the	O
mid-1990s	O
class	B-Application
browsers	I-Application
became	O
an	O
expected	O
part	O
of	O
any	O
graphic	O
development	O
environment	O
.	O
</s>
<s>
Modern	O
class	B-Application
browsers	I-Application
fall	O
into	O
three	O
general	O
categories	O
:	O
the	O
columnar	O
browsers	O
,	O
the	O
outline	O
browsers	O
,	O
and	O
the	O
diagram	O
browsers	O
.	O
</s>
<s>
Continuing	O
the	O
Smalltalk	B-Application
tradition	O
,	O
columnar	O
browsers	O
display	O
the	O
class	O
hierarchy	O
from	O
left	O
to	O
right	O
in	O
a	O
series	O
of	O
columns	O
.	O
</s>
<s>
Systems	O
with	O
roots	O
in	O
Microsoft	B-Application
Windows	I-Application
tend	O
to	O
use	O
an	O
outline-form	O
browser	O
,	O
often	O
with	O
colorful	O
(	O
if	O
cryptic	O
)	O
icons	O
to	O
denote	O
classes	O
and	O
their	O
attributes	O
.	O
</s>
<s>
In	O
the	O
early	O
years	O
of	O
the	O
21st	O
century	O
class	B-Application
browsers	I-Application
began	O
to	O
morph	O
into	O
modeling	O
tools	O
,	O
where	O
programmers	O
could	O
not	O
only	O
visualize	O
their	O
class	O
hierarchy	O
as	O
a	O
diagram	O
,	O
but	O
also	O
add	O
classes	O
to	O
their	O
code	O
by	O
adding	O
them	O
to	O
the	O
diagram	O
.	O
</s>
<s>
Most	O
of	O
these	O
visualization	O
systems	O
have	O
been	O
based	O
on	O
some	O
form	O
of	O
the	O
Unified	B-Language
Modeling	I-Language
Language	I-Language
(	O
UML	B-Language
)	O
.	O
</s>
<s>
As	O
development	O
environments	O
add	O
refactoring	O
features	O
,	O
many	O
of	O
these	O
features	O
have	O
been	O
implemented	O
in	O
the	O
class	B-Application
browser	I-Application
as	O
well	O
as	O
in	O
text	O
editors	O
.	O
</s>
<s>
An	O
early	O
add-on	O
for	O
Digitalk	O
Smalltalk	B-Application
was	O
a	O
logic	B-Application
browser	I-Application
for	O
Prolog	B-Language
rules	O
encapsulated	O
as	O
clauses	O
within	O
classes	O
.	O
</s>
<s>
More	O
recent	O
logic	B-Application
browsers	I-Application
have	O
appeared	O
as	O
and	O
(	O
Smalltalk	B-Application
Open	O
Unification	O
Language	O
with	O
LiCor	O
,	O
or	O
library	O
for	O
code	O
reasoning	O
)	O
for	O
Squeak	B-Operating_System
and	O
VisualWorks	O
Smalltalk	B-Application
.	O
</s>
<s>
A	O
logic	B-Application
browser	I-Application
provides	O
an	O
interface	O
to	O
Prolog	B-Language
implemented	O
in	O
Smalltalk	B-Application
(	O
Lisp	B-Language
engines	O
have	O
often	O
been	O
implemented	O
in	O
Smalltalk	B-Application
)	O
.	O
</s>
<s>
Visual	B-Application
Prolog	I-Application
and	O
XPCE	O
provide	O
comparable	O
rule	O
browsing	O
.	O
</s>
<s>
The	O
comments	O
of	O
Alan	O
Kay	O
on	O
the	O
parallel	O
of	O
Smalltalk	B-Application
and	O
Prolog	B-Language
emerged	O
in	O
the	O
same	O
timeframe	O
but	O
with	O
very	O
little	O
cross-fertilization	O
.	O
</s>
<s>
The	O
interest	O
in	O
XSB	O
prolog	B-Language
for	O
XUL	B-Application
and	O
the	O
migration	O
of	O
AMZI	O
!	O
</s>
<s>
prolog	B-Language
to	O
the	O
Eclipse	B-Application
IDE	I-Application
are	O
current	O
paths	O
in	O
logic	B-Application
browser	I-Application
evolution	O
.	O
</s>
<s>
Rules	O
encapsulated	O
in	O
classes	O
can	O
be	O
found	O
in	O
Logtalk	B-Language
and	O
several	O
OOP	B-Language
Prolog	B-Language
variants	O
such	O
as	O
,	O
and	O
as	O
well	O
as	O
mainstream	O
SICStus	B-Language
.	O
</s>
<s>
One	O
variant	O
of	O
the	O
Seaside	B-Application
web	I-Application
framework	I-Application
in	O
Smalltalk	B-Application
permits	O
a	O
class	B-Application
browser	I-Application
to	O
be	O
opened	O
at	O
runtime	O
in	O
the	O
running	O
web	O
browser	O
:	O
an	O
edit	O
to	O
a	O
method	O
then	O
takes	O
immediate	O
effect	O
in	O
the	O
running	O
web	O
application	O
.	O
</s>
<s>
In	O
the	O
case	O
of	O
Vistascript	O
(	O
Vista	O
Smalltalk	B-Application
)	O
for	O
Microsoft	B-Application
IE7	I-Application
,	O
a	O
right-click	O
on	O
the	O
background	O
opens	O
a	O
ClassHierarchyBrowser	O
.	O
</s>
<s>
This	O
is	O
somewhat	O
like	O
editing	O
JavaScript	B-Language
prototypes	O
in	O
a	O
web	O
browser	O
or	O
Ruby	B-Language
,	O
Groovy	B-Application
or	O
Jython	B-Language
classes	O
in	O
an	O
IDE	B-Application
running	O
in	O
a	O
JVM	B-Language
.	O
</s>
