<s>
A	O
program	B-Application
transformation	I-Application
is	O
any	O
operation	O
that	O
takes	O
a	O
computer	B-Application
program	I-Application
and	O
generates	O
another	O
program	O
.	O
</s>
<s>
In	O
many	O
cases	O
the	O
transformed	O
program	O
is	O
required	O
to	O
be	O
semantically	O
equivalent	O
to	O
the	O
original	O
,	O
relative	O
to	O
a	O
particular	O
formal	B-Application
semantics	I-Application
and	O
in	O
fewer	O
cases	O
the	O
transformations	O
result	O
in	O
programs	O
that	O
semantically	O
differ	O
from	O
the	O
original	O
in	O
predictable	O
ways	O
.	O
</s>
<s>
While	O
the	O
transformations	O
can	O
be	O
performed	O
manually	O
,	O
it	O
is	O
often	O
more	O
practical	O
to	O
use	O
a	O
program	B-Application
transformation	I-Application
system	I-Application
that	O
applies	O
specifications	O
of	O
the	O
required	O
transformations	O
.	O
</s>
<s>
Program	B-Application
transformations	I-Application
may	O
be	O
specified	O
as	O
automated	O
procedures	O
that	O
modify	O
compiler	O
data	O
structures	O
(	O
e.g.	O
</s>
<s>
abstract	B-Data_Structure
syntax	I-Data_Structure
trees	I-Data_Structure
)	O
representing	O
the	O
program	O
text	O
,	O
or	O
may	O
be	O
specified	O
more	O
conveniently	O
using	O
patterns	O
or	O
templates	O
representing	O
parameterized	O
source	O
code	O
fragments	O
.	O
</s>
<s>
A	O
practical	O
requirement	O
for	O
source	B-Application
code	I-Application
transformation	I-Application
systems	O
is	O
that	O
they	O
be	O
able	O
to	O
effectively	O
process	O
programs	O
written	O
in	O
a	O
programming	O
language	O
.	O
</s>
<s>
This	O
usually	O
requires	O
integration	O
of	O
a	O
full	O
front-end	O
for	O
the	O
programming	O
language	O
of	O
interest	O
,	O
including	O
source	O
code	O
parsing	B-Language
,	O
building	O
internal	O
program	O
representations	O
of	O
code	O
structures	O
,	O
the	O
meaning	O
of	O
program	O
symbols	O
,	O
useful	O
static	O
analyses	O
,	O
and	O
regeneration	O
of	O
valid	O
source	O
code	O
from	O
transformed	O
program	O
representations	O
.	O
</s>
<s>
The	O
problem	O
of	O
building	O
and	O
integrating	O
adequate	O
front	O
ends	O
for	O
conventional	O
languages	O
(	O
Java	B-Language
,	O
C++	B-Language
,	O
PHP	B-Application
etc	O
.	O
)	O
</s>
<s>
may	O
be	O
of	O
equal	O
difficulty	O
as	O
building	O
the	O
program	B-Application
transformation	I-Application
system	I-Application
itself	O
because	O
of	O
the	O
complexity	O
of	O
such	O
languages	O
.	O
</s>
