<s>
The	O
Syntax	B-Application
Definition	I-Application
Formalism	I-Application
(	O
SDF	O
)	O
is	O
a	O
metasyntax	O
used	O
to	O
define	O
context-free	O
grammars	O
:	O
that	O
is	O
,	O
a	O
formal	O
way	O
to	O
describe	O
formal	O
languages	O
.	O
</s>
<s>
A	O
parser	B-Language
and	O
parser	B-Language
generator	I-Language
for	O
SDF	O
specifications	O
are	O
provided	O
as	O
part	O
of	O
the	O
free	O
ASF+SDF	O
Meta	O
Environment	O
.	O
</s>
<s>
These	O
operate	O
using	O
the	O
SGLR	O
(	O
Scannerless	B-Application
GLR	B-Application
parser	I-Application
)	O
.	O
</s>
<s>
An	O
SDF	O
parser	B-Language
outputs	O
parse	O
trees	O
or	O
,	O
in	O
the	O
case	O
of	O
ambiguities	O
,	O
parse	O
forests	O
.	O
</s>
