<s>
In	O
computer	B-General_Concept
science	I-General_Concept
,	O
an	O
LL	B-Language
parser	I-Language
(	O
Left-to-right	O
,	O
leftmost	O
derivation	O
)	O
is	O
a	O
top-down	B-Application
parser	I-Application
for	O
a	O
restricted	O
context-free	O
language	O
.	O
</s>
<s>
An	O
LL	B-Language
parser	I-Language
is	O
called	O
an	O
LL(k )	O
parser	O
if	O
it	O
uses	O
k	O
tokens	O
of	O
lookahead	O
when	O
parsing	O
a	O
sentence	O
.	O
</s>
<s>
An	O
LL	B-Language
parser	I-Language
is	O
called	O
LL-regular	O
(	O
LLR	O
)	O
if	O
it	O
parses	O
an	O
LL-regular	O
language	O
.	O
</s>
<s>
LL	O
grammars	O
,	O
particularly	O
LL(1 )	O
grammars	O
,	O
are	O
of	O
great	O
practical	O
interest	O
,	O
as	O
parsers	O
for	O
these	O
grammars	O
are	O
easy	O
to	O
construct	O
,	O
and	O
many	O
computer	B-Language
languages	I-Language
are	O
designed	O
to	O
be	O
LL(1 )	O
for	O
this	O
reason	O
.	O
</s>
<s>
LL	B-Language
parsers	I-Language
may	O
be	O
table-based	O
,	O
i.e.	O
</s>
<s>
similar	O
to	O
LR	B-Application
parsers	I-Application
,	O
but	O
LL	O
grammars	O
can	O
also	O
be	O
parsed	O
by	O
recursive	B-Application
descent	I-Application
parsers	I-Application
.	O
</s>
<s>
The	O
parser	O
is	O
a	O
deterministic	B-Application
pushdown	I-Application
automaton	I-Application
with	O
the	O
ability	O
to	O
peek	O
on	O
the	O
next	O
input	O
symbols	O
without	O
reading	O
.	O
</s>
<s>
Below	O
follows	O
a	O
C++	O
implementation	O
of	O
a	O
table-based	O
LL	B-Language
parser	I-Language
for	O
the	O
example	O
language	O
:	O
</s>
<s>
This	O
perception	O
changed	O
gradually	O
after	O
the	O
release	O
of	O
the	O
Purdue	B-Application
Compiler	I-Application
Construction	I-Application
Tool	I-Application
Set	I-Application
around	O
1992	O
,	O
when	O
it	O
was	O
demonstrated	O
that	O
many	O
programming	O
languages	O
can	O
be	O
parsed	O
efficiently	O
by	O
an	O
LL(k )	O
parser	O
without	O
triggering	O
the	O
worst-case	O
behavior	O
of	O
the	O
parser	O
.	O
</s>
<s>
Moreover	O
,	O
in	O
certain	O
cases	O
LL	B-Language
parsing	I-Language
is	O
feasible	O
even	O
with	O
unlimited	O
lookahead	O
.	O
</s>
<s>
By	O
contrast	O
,	O
traditional	O
parser	O
generators	O
like	O
yacc	B-Application
use	O
LALR(1 )	O
parser	O
tables	O
to	O
construct	O
a	O
restricted	O
LR	B-Application
parser	I-Application
with	O
a	O
fixed	O
one-token	O
lookahead	O
.	O
</s>
<s>
Left	B-Application
recursion	I-Application
will	O
cause	O
a	O
FIRST/FIRST	O
conflict	O
with	O
all	O
alternatives	O
.	O
</s>
<s>
For	O
a	O
general	O
method	O
,	O
see	O
removing	O
left	B-Application
recursion	I-Application
.	O
</s>
<s>
A	O
simple	O
example	O
for	O
left	B-Application
recursion	I-Application
removal	O
:	O
</s>
<s>
Now	O
there	O
is	O
no	O
left	B-Application
recursion	I-Application
and	O
no	O
conflicts	O
on	O
either	O
of	O
the	O
rules	O
.	O
</s>
