<s>
Lithe	B-Language
is	O
an	O
experimental	O
programming	O
language	O
created	O
in	O
1982	O
by	O
David	O
Sandberg	O
at	O
the	O
University	O
of	O
Washington	O
which	O
allows	O
the	O
programmer	O
to	O
freely	O
choose	O
their	O
own	O
syntax	O
.	O
</s>
<s>
Lithe	B-Language
combines	O
the	O
ideas	O
of	O
syntax-directed	B-Application
translation	I-Application
and	O
classes	O
in	O
a	O
novel	O
manner	O
that	O
results	O
in	O
a	O
remarkably	O
simple	O
yet	O
powerful	O
language	O
.	O
</s>
<s>
The	O
standard	O
class-based	B-Application
programming	I-Application
model	O
does	O
not	O
specify	O
a	O
mechanism	O
by	O
which	O
to	O
manipulate	O
objects	O
:	O
where	O
Smalltalk	B-Application
uses	O
message	O
passing	O
,	O
Lithe	B-Language
uses	O
syntax-directed	B-Application
translation	I-Application
(	O
SDT	O
)	O
.	O
</s>
<s>
Lithe	B-Language
merges	O
SDT	O
with	O
the	O
class	O
model	O
by	O
using	O
classes	O
as	O
the	O
non-terminal	O
alphabet	O
of	O
the	O
grammar	O
.	O
</s>
<s>
Since	O
the	O
grammar	O
class	O
used	O
by	O
Lithe	B-Language
properly	O
contains	O
all	O
context-free	O
grammars	O
,	O
a	O
wide	O
variety	O
of	O
syntax	O
can	O
be	O
described	O
,	O
and	O
SDT	O
provides	O
a	O
simple	O
way	O
to	O
attach	O
semantics	O
to	O
any	O
such	O
syntax	O
.	O
</s>
<s>
The	O
package	O
is	O
the	O
unit	O
of	O
program	B-Architecture
modularity	I-Architecture
in	O
Lithe	B-Language
.	O
</s>
<s>
Information	B-Application
hiding	I-Application
is	O
achieved	O
by	O
requiring	O
both	O
export	O
keywords	O
on	O
those	O
rules	O
and	O
classes	O
that	O
are	O
to	O
be	O
seen	O
outside	O
a	O
package	O
and	O
that	O
the	O
source	O
package	O
names	O
be	O
included	O
in	O
the	O
with	O
clause	O
of	O
the	O
consumer	O
package	O
.	O
</s>
<s>
Programming	O
in	O
Lithe	B-Language
consists	O
of	O
defining	O
rule-action	O
pairs	O
and	O
classes	O
.	O
</s>
<s>
After	O
this	O
rule-action	O
pair	O
has	O
been	O
defined	O
,	O
it	O
can	O
be	O
freely	O
used	O
within	O
Lithe	B-Language
source	O
code	O
,	O
for	O
example	O
,	O
the	O
following	O
expression	O
will	O
thereafter	O
be	O
valid	O
:	O
</s>
<s>
Note	O
that	O
the	O
Lithe	B-Language
description	O
swaps	O
the	O
left	O
and	O
right	O
sides	O
of	O
the	O
BNF	O
one	O
,	O
then	O
adds	O
a	O
name	O
to	O
each	O
nonterminal	O
in	O
the	O
BNF	O
right-hand	O
side	O
.	O
</s>
