<s>
PackCC	B-Application
is	O
a	O
parser	B-Language
generator	I-Language
for	O
C	B-Language
.	O
Its	O
main	O
features	O
are	O
as	O
follows	O
:	O
</s>
<s>
Generates	O
a	O
parser	O
in	O
written	O
C	B-Language
from	O
a	O
grammar	O
described	O
in	O
a	O
PEG	O
,	O
</s>
<s>
Gives	O
a	O
parser	O
great	O
efficiency	O
by	O
packrat	B-Application
parsing	I-Application
,	O
</s>
<s>
Supports	O
direct	O
and	O
indirect	O
left-recursive	B-Application
grammar	O
rules	O
,	O
</s>
<s>
Generates	O
a	O
thread-safe	B-Operating_System
and	O
reentrant	B-Operating_System
parser	O
,	O
</s>
<s>
The	O
PEG	O
is	O
a	O
top-down	O
parsing	O
language	O
,	O
and	O
is	O
similar	O
to	O
the	O
regular	B-Language
expression	I-Language
grammar	O
.	O
</s>
<s>
Compared	O
with	O
a	O
bottom-up	O
parsing	O
language	O
,	O
like	O
Yacc	B-Application
's	O
one	O
,	O
the	O
PEG	O
is	O
much	O
more	O
intuitive	O
and	O
cannot	O
be	O
ambiguous	O
.	O
</s>
<s>
The	O
generated	O
parser	O
can	O
parse	O
inputs	O
very	O
efficiently	O
by	O
packrat	B-Application
parsing	I-Application
.	O
</s>
<s>
The	O
packrat	B-Application
parsing	I-Application
is	O
the	O
recursive	B-Application
descent	I-Application
parsing	I-Application
algorithm	O
that	O
is	O
accelerated	O
using	O
memoization	O
.	O
</s>
<s>
By	O
using	O
packrat	B-Application
parsing	I-Application
,	O
any	O
input	O
can	O
be	O
parsed	O
in	O
linear	O
time	O
.	O
</s>
<s>
Unlike	O
common	O
packrat	B-Application
parsers	I-Application
,	O
PackCC	B-Application
can	O
support	O
direct	O
and	O
indirect	O
left-recursive	B-Application
grammar	O
rules	O
.	O
</s>
<s>
Actually	O
,	O
it	O
uses	O
many	O
goto	O
statements	O
,	O
but	O
the	O
control	O
flows	O
are	O
much	O
more	O
traceable	O
than	O
goto	O
spaghetti	O
storms	O
generated	O
by	O
some	O
other	O
parser	B-Language
generators	I-Language
.	O
</s>
<s>
PackCC	B-Application
itself	O
is	O
under	O
MIT	B-License
license	I-License
,	O
but	O
the	O
generated	O
code	O
can	O
be	O
distributed	O
under	O
any	O
license	O
or	O
can	O
be	O
used	O
in	O
proprietary	O
software	O
.	O
</s>
<s>
Note	O
that	O
left-recursive	B-Application
grammar	O
rules	O
are	O
included	O
.	O
</s>
