<s>
In	O
computer	B-General_Concept
programming	I-General_Concept
,	O
a	O
programming	B-Application
language	I-Application
implementation	I-Application
is	O
a	O
system	O
for	O
executing	O
computer	B-Application
programs	I-Application
.	O
</s>
<s>
There	O
are	O
two	O
general	O
approaches	O
to	O
programming	B-Application
language	I-Application
implementation	I-Application
:	O
</s>
<s>
Interpretation	B-Application
:	O
The	O
program	O
is	O
read	O
as	O
input	O
by	O
an	O
interpreter	B-Application
,	O
which	O
performs	O
the	O
actions	O
written	O
in	O
the	O
program	O
.	O
</s>
<s>
Compilation	B-Language
:	O
The	O
program	O
is	O
read	O
by	O
a	O
compiler	B-Language
,	O
which	O
translates	O
it	O
into	O
some	O
other	O
language	O
,	O
such	O
as	O
bytecode	O
or	O
machine	B-Language
code	I-Language
.	O
</s>
<s>
The	O
translated	O
code	O
may	O
either	O
be	O
directly	O
executed	B-General_Concept
by	O
hardware	O
,	O
or	O
serve	O
as	O
input	O
to	O
another	O
interpreter	B-Application
or	O
another	O
compiler	B-Language
.	O
</s>
<s>
An	O
interpreter	B-Application
is	O
composed	O
of	O
two	O
parts	O
:	O
a	O
parser	B-Language
and	O
an	O
evaluator	B-Application
.	O
</s>
<s>
After	O
a	O
program	O
is	O
read	O
as	O
input	O
by	O
an	O
interpreter	B-Application
,	O
it	O
is	O
processed	O
by	O
the	O
parser	B-Language
.	O
</s>
<s>
The	O
parser	B-Language
breaks	O
the	O
program	O
into	O
language	O
components	O
to	O
form	O
a	O
parse	O
tree	O
.	O
</s>
<s>
The	O
evaluator	B-Application
then	O
uses	O
the	O
parse	O
tree	O
to	O
execute	O
the	O
program	O
.	O
</s>
<s>
A	O
virtual	B-Architecture
machine	I-Architecture
is	O
a	O
special	O
type	O
of	O
interpreter	B-Application
that	O
interprets	O
bytecode	O
.	O
</s>
<s>
Bytecode	O
is	O
a	O
portable	B-Architecture
low-level	O
code	O
similar	O
to	O
machine	B-Language
code	I-Language
,	O
though	O
it	O
is	O
generally	O
executed	B-General_Concept
on	O
a	O
virtual	B-Architecture
machine	I-Architecture
instead	O
of	O
a	O
physical	O
machine	O
.	O
</s>
<s>
To	O
improve	O
their	O
efficiencies	O
,	O
many	O
programming	O
languages	O
such	O
as	O
Java	B-Language
,	O
Python	B-Language
,	O
and	O
C#	B-Application
are	O
compiled	B-Language
to	O
bytecode	O
before	O
being	O
interpreted	O
.	O
</s>
<s>
Some	O
virtual	B-Architecture
machines	I-Architecture
include	O
a	O
just-in-time	O
(	O
JIT	O
)	O
compiler	B-Language
to	O
improve	O
the	O
efficiency	O
of	O
bytecode	O
execution	O
.	O
</s>
<s>
While	O
the	O
bytecode	O
is	O
being	O
executed	B-General_Concept
by	O
the	O
virtual	B-Architecture
machine	I-Architecture
,	O
if	O
the	O
JIT	O
compiler	B-Language
determines	O
that	O
a	O
portion	O
of	O
the	O
bytecode	O
will	O
be	O
used	O
repeatedly	O
,	O
it	O
compiles	B-Language
that	O
particular	O
portion	O
to	O
machine	B-Language
code	I-Language
.	O
</s>
<s>
The	O
JIT	O
compiler	B-Language
then	O
stores	O
the	O
machine	B-Language
code	I-Language
in	O
memory	B-Architecture
so	O
that	O
it	O
can	O
be	O
used	O
by	O
the	O
virtual	B-Architecture
machine	I-Architecture
.	O
</s>
<s>
JIT	O
compilers	B-Language
try	O
to	O
strike	O
a	O
balance	O
between	O
longer	O
compilation	B-Language
time	O
and	O
faster	O
execution	O
time	O
.	O
</s>
<s>
A	O
compiler	B-Language
translates	O
a	O
program	O
written	O
in	O
one	O
language	O
into	O
another	O
language	O
.	O
</s>
<s>
Most	O
compilers	B-Language
are	O
organized	O
into	O
three	O
stages	O
:	O
a	O
front	O
end	O
,	O
an	O
optimizer	O
,	O
and	O
a	O
back	O
end	O
.	O
</s>
<s>
It	O
makes	O
sure	O
the	O
program	O
is	O
valid	O
and	O
transforms	O
it	O
into	O
an	O
intermediate	B-Application
representation	I-Application
,	O
a	O
data	O
structure	O
used	O
by	O
the	O
compiler	B-Language
to	O
represent	O
the	O
program	O
.	O
</s>
<s>
The	O
optimizer	O
improves	O
the	O
intermediate	B-Application
representation	I-Application
to	O
increase	O
the	O
speed	O
or	O
reduce	O
the	O
size	O
of	O
the	O
executable	B-Application
which	O
is	O
ultimately	O
produced	O
by	O
the	O
compiler	B-Language
.	O
</s>
<s>
The	O
back	O
end	O
converts	O
the	O
optimized	O
intermediate	B-Application
representation	I-Application
into	O
the	O
output	O
language	O
of	O
the	O
compiler	B-Language
.	O
</s>
<s>
If	O
a	O
compiler	B-Language
of	O
a	O
given	O
high	B-Language
level	I-Language
language	I-Language
produces	O
another	O
high	B-Language
level	I-Language
language	I-Language
,	O
it	O
is	O
called	O
a	O
transpiler	B-Language
.	O
</s>
<s>
Transpilers	B-Language
can	O
be	O
used	O
to	O
extend	O
existing	O
languages	O
or	O
to	O
simplify	O
compiler	B-Language
development	O
by	O
exploiting	O
portable	B-Architecture
and	O
well-optimized	O
implementations	O
of	O
other	O
languages	O
(	O
such	O
as	O
C	B-Language
)	O
.	O
</s>
<s>
Many	O
combinations	O
of	O
interpretation	B-Application
and	O
compilation	B-Language
are	O
possible	O
,	O
and	O
many	O
modern	O
programming	B-Application
language	I-Application
implementations	I-Application
include	O
elements	O
of	O
both	O
.	O
</s>
<s>
For	O
example	O
,	O
the	O
Smalltalk	B-Application
programming	I-Application
language	I-Application
is	O
conventionally	O
implemented	O
by	O
compilation	B-Language
into	O
bytecode	O
,	O
which	O
is	O
then	O
either	O
interpreted	O
or	O
compiled	B-Language
by	O
a	O
virtual	B-Architecture
machine	I-Architecture
.	O
</s>
<s>
Since	O
Smalltalk	B-Application
bytecode	O
is	O
run	O
on	O
a	O
virtual	B-Architecture
machine	I-Architecture
,	O
it	O
is	O
portable	B-Architecture
across	O
different	O
hardware	O
platforms	O
.	O
</s>
<s>
Different	O
implementations	O
can	O
be	O
written	O
in	O
different	O
languages	O
and	O
can	O
use	O
different	O
methods	O
to	O
compile	B-Language
or	O
interpret	O
code	O
.	O
</s>
<s>
For	O
example	O
,	O
implementations	O
of	O
Python	B-Language
include	O
:	O
</s>
