<s>
Hop	B-Application
is	O
a	O
Lisp-like	O
programming	O
language	O
by	O
Manuel	O
Serrano	O
for	O
web	O
2.0	O
and	O
also	O
the	O
name	O
of	O
the	O
web	O
broker	O
(	O
server	B-Application
and	O
proxy	O
)	O
that	O
implements	O
this	O
language	O
.	O
</s>
<s>
It	O
is	O
written	O
in	O
Bigloo	B-General_Concept
Scheme	B-Language
.	O
</s>
<s>
Hop	B-Application
is	O
a	O
stratified	O
language	O
,	O
which	O
means	O
that	O
a	O
single	O
program	O
file	O
contains	O
instructions	O
for	O
both	O
the	O
server	B-Application
and	O
the	O
client	O
.	O
</s>
<s>
The	O
server	B-Application
executes	O
CPU	O
demanding	O
computations	O
and	O
operations	O
that	O
require	O
system	O
privileges	O
for	O
accessing	O
files	O
or	O
other	O
resources	O
.	O
</s>
<s>
Lines	O
1	O
and	O
2	O
result	O
in	O
a	O
service	O
definition	O
on	O
the	O
server	B-Application
.	O
</s>
<s>
It	O
instructs	O
a	O
client	O
(	O
browser	O
)	O
to	O
display	O
a	O
button	O
with	O
the	O
label	O
"	O
Server	B-Application
time	O
"	O
and	O
to	O
send	O
a	O
request	O
to	O
the	O
server	B-Application
when	O
the	O
user	O
clicks	O
on	O
the	O
button	O
.	O
</s>
<s>
Hop	B-Application
automatically	O
generates	O
all	O
the	O
instructions	O
needed	O
for	O
the	O
communication	O
between	O
the	O
client	O
and	O
the	O
server	B-Application
.	O
</s>
<s>
Hop	B-Application
is	O
based	O
on	O
Scheme	B-Language
.	O
</s>
<s>
Therefore	O
a	O
Hop	B-Application
program	O
is	O
essentially	O
a	O
list	O
of	O
words	O
and/or	O
lists	O
that	O
start	O
and	O
end	O
with	O
parentheses	O
.	O
</s>
<s>
Function	O
names	O
in	O
Hop	B-Application
may	O
contain	O
characters	O
other	O
than	O
letters	O
and	O
numbers	O
.	O
</s>
<s>
Therefore	O
the	O
syntax	O
of	O
Hop	B-Application
looks	O
very	O
similar	O
to	O
HTML	O
(	O
by	O
design	O
)	O
.	O
</s>
<s>
The	O
Hop	B-Application
expression	O
"	O
(	O
<HTML>	O
content	O
)	O
"	O
is	O
similar	O
to	O
the	O
HTML	O
expression	O
"	O
content	O
"	O
.	O
</s>
<s>
The	O
$	O
character	O
in	O
"	O
$	O
server-date	O
"	O
indicates	O
that	O
the	O
server	B-Application
should	O
substitute	O
the	O
variable	O
name	O
"	O
server-date	O
"	O
with	O
the	O
variable	O
's	O
value	O
before	O
sending	O
the	O
HTML	O
to	O
the	O
client	O
.	O
</s>
<s>
The	O
"	O
with-hop	O
"	O
function	O
in	O
"	O
(	O
with-hop	O
(	O
...	O
)	O
(	O
...	O
)	O
)	O
"	O
is	O
a	O
special	O
function	O
that	O
delegates	O
work	O
to	O
the	O
server	B-Application
and	O
takes	O
two	O
parameters	O
.	O
</s>
<s>
The	O
first	O
parameter	O
contains	O
the	O
request	O
the	O
client	O
should	O
send	O
to	O
the	O
server	B-Application
asynchronously	O
.	O
</s>
<s>
The	O
second	O
parameter	O
contains	O
the	O
callback	O
function	O
that	O
the	O
client	O
should	O
invoke	O
when	O
the	O
response	O
arrives	O
from	O
the	O
server	B-Application
.	O
</s>
<s>
"	O
(	O
lambda	O
(	O
h	O
)	O
(	O
alert	O
h	O
)	O
)	O
"	O
is	O
an	O
anonymous	O
function	O
that	O
takes	O
a	O
single	O
input	O
parameter	O
"	O
(	O
h	O
)	O
"	O
,	O
which	O
contains	O
the	O
server	B-Application
response	O
when	O
the	O
function	O
is	O
called	O
.	O
</s>
<s>
Given	O
its	O
recent	O
introduction	O
,	O
Hop	B-Application
currently	O
exhibits	O
a	O
number	O
of	O
weaknesses	O
.	O
</s>
