<s>
The	O
basic	O
control	O
structures	O
of	O
Perl	B-Language
are	O
similar	O
to	O
those	O
used	O
in	O
C	B-Language
and	O
Java	B-Language
,	O
but	O
they	O
have	O
been	O
extended	O
in	O
several	O
ways	O
.	O
</s>
<s>
In	O
the	O
following	O
,	O
label	O
is	O
an	O
optional	O
identifier	O
terminated	O
by	O
a	O
colon	O
,	O
and	O
block	O
is	O
a	O
sequence	O
of	O
one	O
of	O
more	O
Perl	B-Language
statements	O
surrounded	O
by	O
braces	O
.	O
</s>
<s>
All	O
looping	O
constructs	O
except	O
for	O
the	O
C-style	O
for-loop	O
can	O
have	O
a	O
continue	O
block	O
that	O
is	O
executed	O
after	O
each	O
iteration	O
of	O
the	O
loop	O
body	O
,	O
before	O
the	O
loop	O
condition	O
is	O
evaluated	O
again	O
.	O
</s>
<s>
This	O
is	O
the	O
so-called	O
C-style	O
for	O
loop	O
.	O
</s>
<s>
The	O
label	O
block	O
construct	O
is	O
a	O
bit	O
of	O
an	O
oddity	O
:	O
Perl	B-Language
treats	O
a	O
bare	O
block	O
with	O
or	O
without	O
a	O
label	O
as	O
a	O
loop	O
that	O
is	O
executed	O
once	O
.	O
</s>
<s>
Perl	B-Language
provides	O
three	O
loop	O
control	O
keywords	O
that	O
all	O
accept	O
an	O
optional	O
loop	O
label	O
as	O
an	O
argument	O
.	O
</s>
<s>
The	O
loop	O
control	O
keywords	O
are	O
treated	O
as	O
expressions	O
in	O
Perl	B-Language
,	O
not	O
as	O
statements	O
like	O
in	O
C	B-Language
or	O
Java	B-Language
.	O
</s>
<s>
where	O
block	O
is	O
a	O
sequence	O
of	O
one	O
of	O
more	O
Perl	B-Language
statements	O
surrounded	O
by	O
braces	O
.	O
</s>
<s>
This	O
means	O
that	O
the	O
strings	O
"	O
0.0	O
"	O
,	O
"	O
00	O
"	O
,	O
"	O
-0	B-Algorithm
"	O
,	O
and	O
"	O
0	O
but	O
true	O
"	O
are	O
all	O
true	O
,	O
even	O
though	O
their	O
value	O
would	O
be	O
converted	O
to	O
0	O
in	O
a	O
numeric	O
context	O
;	O
values	O
like	O
these	O
are	O
sometimes	O
used	O
when	O
a	O
successful	O
operation	O
needs	O
to	O
return	O
0	O
.	O
</s>
<s>
Perl	B-Language
also	O
provides	O
variants	O
of	O
the	O
loop	O
and	O
conditional	O
constructs	O
that	O
work	O
on	O
a	O
simple	O
statement	O
(	O
an	O
expression	O
evaluated	O
for	O
its	O
side-effects	O
)	O
instead	O
of	O
a	O
block	O
:	O
</s>
<s>
There	O
are	O
two	O
forms	O
of	O
goto	B-Application
in	O
Perl	B-Language
:	O
</s>
<s>
For	O
example	O
,	O
when	O
attempting	O
to	O
preserve	O
error	O
status	O
in	O
$	O
?,	O
some	O
modules	O
will	O
use	O
goto	B-Application
like	O
this	O
:	O
</s>
<s>
The	O
second	O
form	O
is	O
called	O
a	O
tail	B-Language
call	I-Language
,	O
and	O
is	O
used	O
to	O
enhance	O
the	O
performance	O
of	O
certain	O
kinds	O
of	O
constructs	O
where	O
Perl	B-Language
's	O
default	O
stack	O
management	O
would	O
perform	O
non-optimally	O
.	O
</s>
