<s>
XPL0	B-Language
is	O
a	O
computer	O
programming	O
language	O
that	O
is	O
essentially	O
a	O
cross	O
between	O
Pascal	B-Application
and	O
C	B-Language
.	O
It	O
looks	O
somewhat	O
like	O
Pascal	B-Application
but	O
works	O
more	O
like	O
C	B-Language
.	O
It	O
was	O
created	O
in	O
1976	O
by	O
Peter	O
J	O
.	O
R	O
.	O
Boyle	O
who	O
wanted	O
a	O
high-level	O
language	O
for	O
his	O
microcomputer	B-Architecture
and	O
wanted	O
something	O
more	O
sophisticated	O
than	O
BASIC	O
,	O
which	O
was	O
the	O
dominant	O
language	O
for	O
personal	O
computers	O
at	O
the	O
time	O
.	O
</s>
<s>
XPL0	B-Language
is	O
based	O
on	O
PL/0	B-Language
,	O
an	O
example	O
compiler	O
in	O
the	O
book	O
Algorithms	O
+	O
Data	O
Structures	O
=	O
Programs	O
by	O
Niklaus	O
Wirth	O
.	O
</s>
<s>
The	O
first	O
XPL0	B-Language
compiler	O
was	O
written	O
in	O
ALGOL	B-Language
.	O
</s>
<s>
It	O
generated	O
instructions	O
for	O
a	O
pseudo-machine	O
that	O
was	O
implemented	O
as	O
an	O
interpreter	O
on	O
a	O
Digital	O
Group	O
computer	O
based	O
on	O
the	O
6502	B-General_Concept
microprocessor	I-General_Concept
.	O
</s>
<s>
The	O
compiler	O
was	O
converted	O
from	O
ALGOL	B-Language
to	O
XPL0	B-Language
and	O
was	O
then	O
able	O
to	O
compile	O
itself	O
and	O
run	O
on	O
a	O
microcomputer	B-Architecture
.	O
</s>
<s>
XPL0	B-Language
soon	O
proved	O
its	O
worth	O
in	O
a	O
variety	O
of	O
products	O
based	O
on	O
the	O
6502	B-General_Concept
.	O
</s>
<s>
These	O
embedded	B-Architecture
systems	I-Architecture
would	O
otherwise	O
have	O
had	O
their	O
code	O
written	O
in	O
assembly	B-Language
language	I-Language
,	O
which	O
is	O
much	O
more	O
tedious	O
to	O
do	O
.	O
</s>
<s>
Boyle	O
used	O
XPL0	B-Language
to	O
write	O
a	O
disk	B-Operating_System
operating	I-Operating_System
system	I-Operating_System
called	O
Apex	O
.	O
</s>
<s>
Beginning	O
in	O
1980	O
this	O
was	O
sold	O
,	O
along	O
with	O
XPL0	B-Language
,	O
as	O
an	O
alternative	O
to	O
Apple	B-Operating_System
DOS	I-Operating_System
for	O
the	O
AppleII	O
computer	O
,	O
which	O
was	O
based	O
on	O
the	O
6502	B-General_Concept
.	O
</s>
<s>
Since	O
those	O
early	O
years	O
XPL0	B-Language
has	O
been	O
implemented	O
on	O
a	O
dozen	O
processors	O
,	O
and	O
many	O
features	O
have	O
been	O
added	O
.	O
</s>
<s>
Open	B-Application
source	I-Application
compilers	O
for	O
Windows	O
and	O
MS-DOS	B-Application
on	O
PCs	O
and	O
Linux	B-Application
on	O
the	O
Raspberry	O
Pi	O
are	O
available	O
from	O
the	O
link	O
below	O
.	O
</s>
<s>
This	O
is	O
how	O
the	O
traditional	O
Hello	O
World	O
program	O
is	O
coded	O
in	O
XPL0	B-Language
:	O
</s>
<s>
In	O
XPL0	B-Language
all	O
names	O
must	O
be	O
declared	O
before	O
they	O
can	O
be	O
used	O
.	O
</s>
<s>
Graphics	O
has	O
been	O
a	O
feature	O
of	O
XPL0	B-Language
since	O
its	O
days	O
on	O
the	O
AppleII	O
computer	O
.	O
</s>
