<s>
Modula-3	B-Language
is	O
a	O
programming	O
language	O
conceived	O
as	O
a	O
successor	O
to	O
an	O
upgraded	O
version	O
of	O
Modula-2	B-Language
known	O
as	O
Modula-2	B-Language
+	I-Language
.	O
</s>
<s>
While	O
it	O
has	O
been	O
influential	O
in	O
research	O
circles	O
(	O
influencing	O
the	O
designs	O
of	O
languages	O
such	O
as	O
Java	B-Language
,	O
C#	B-Application
,	O
Python	B-Language
and	O
Nim	B-Application
)	O
it	O
has	O
not	O
been	O
adopted	O
widely	O
in	O
industry	O
.	O
</s>
<s>
Modula-3	B-Language
'	O
s	O
main	O
features	O
are	O
simplicity	O
and	O
safety	O
while	O
preserving	O
the	O
power	O
of	O
a	O
systems-programming	O
language	O
.	O
</s>
<s>
Modula-3	B-Language
aimed	O
to	O
continue	O
the	O
Pascal	B-Application
tradition	O
of	O
type	O
safety	O
,	O
while	O
introducing	O
new	O
constructs	O
for	O
practical	O
real-world	O
programming	O
.	O
</s>
<s>
In	O
particular	O
Modula-3	B-Language
added	O
support	O
for	O
generic	B-Language
programming	I-Language
(	O
similar	O
to	O
templates	B-Application
)	O
,	O
multithreading	B-Operating_System
,	O
exception	B-General_Concept
handling	I-General_Concept
,	O
garbage	B-General_Concept
collection	I-General_Concept
,	O
object-oriented	B-Language
programming	I-Language
,	O
partial	O
revelation	O
,	O
and	O
explicit	O
marking	O
of	O
unsafe	O
code	O
.	O
</s>
<s>
The	O
design	O
goal	O
of	O
Modula-3	B-Language
was	O
a	O
language	O
that	O
implements	O
the	O
most	O
important	O
features	O
of	O
modern	O
imperative	B-Application
programming	I-Application
languages	I-Application
in	O
quite	O
basic	O
forms	O
.	O
</s>
<s>
Thus	O
allegedly	O
dangerous	O
and	O
complicating	O
features	O
such	O
as	O
multiple	B-Application
inheritance	I-Application
and	O
operator	O
overloading	O
were	O
omitted	O
.	O
</s>
<s>
The	O
Modula-3	B-Language
project	O
started	O
in	O
November	O
1986	O
when	O
Maurice	O
Wilkes	O
wrote	O
to	O
Niklaus	O
Wirth	O
with	O
some	O
ideas	O
for	O
a	O
new	O
version	O
of	O
Modula	B-Language
.	O
</s>
<s>
Wirth	O
had	O
already	O
moved	O
on	O
to	O
Oberon	B-Language
,	O
but	O
had	O
no	O
problems	O
with	O
Wilkes	O
's	O
team	O
continuing	O
development	O
under	O
the	O
Modula	B-Language
name	O
.	O
</s>
<s>
Compilers	B-Language
from	O
DEC	O
and	O
Olivetti	O
soon	O
followed	O
,	O
and	O
3rd	O
party	O
implementations	O
after	O
that	O
.	O
</s>
<s>
Its	O
design	O
was	O
heavily	O
influenced	O
by	O
work	O
on	O
the	O
Modula-2	B-Language
+	I-Language
language	O
in	O
use	O
at	O
SRC	O
and	O
at	O
the	O
Acorn	O
Computers	O
Research	O
Center	O
(	O
ARC	O
,	O
later	O
ORC	O
when	O
Olivetti	O
acquired	O
Acorn	O
)	O
at	O
the	O
time	O
,	O
which	O
was	O
the	O
language	O
in	O
which	O
the	O
operating	O
system	O
for	O
the	O
DEC	B-Device
Firefly	I-Device
multiprocessor	O
VAX	B-Device
workstation	O
was	O
written	O
and	O
in	O
which	O
the	O
Acorn	O
Compiler	B-Language
for	O
Acorn	O
C	B-Language
and	O
Modula	B-Language
Execution	O
Library	O
(	O
CAMEL	O
)	O
at	O
ARC	O
for	O
the	O
ARX	B-Operating_System
operating	O
system	O
project	O
of	O
ARM	B-Architecture
based	O
Acorn	B-Device
Archimedes	I-Device
range	O
of	O
computers	O
was	O
written	O
.	O
</s>
<s>
As	O
the	O
revised	O
Modula-3	B-Language
Report	O
states	O
,	O
the	O
language	O
was	O
influenced	O
by	O
other	O
languages	O
such	O
as	O
Mesa	B-Language
,	O
Cedar	B-Language
,	O
Object	B-Language
Pascal	I-Language
,	O
Oberon	B-Language
and	O
Euclid	B-Language
.	O
</s>
<s>
During	O
the	O
1990s	O
,	O
Modula-3	B-Language
gained	O
considerable	O
currency	O
as	O
a	O
teaching	O
language	O
,	O
but	O
it	O
was	O
never	O
widely	O
adopted	O
for	O
industrial	O
use	O
.	O
</s>
<s>
Contributing	O
to	O
this	O
may	O
have	O
been	O
the	O
demise	O
of	O
DEC	O
,	O
a	O
key	O
Modula-3	B-Language
supporter	O
(	O
especially	O
when	O
it	O
ceased	O
to	O
maintain	O
it	O
effectively	O
before	O
DEC	O
was	O
sold	O
to	O
Compaq	O
in	O
1998	O
)	O
.	O
</s>
<s>
In	O
any	O
case	O
,	O
in	O
spite	O
of	O
Modula-3	B-Language
'	O
s	O
simplicity	O
and	O
power	O
,	O
it	O
appears	O
that	O
there	O
was	O
little	O
demand	O
for	O
a	O
procedural	B-Application
compiled	B-Language
language	I-Language
with	O
restricted	O
implementation	O
of	O
object-oriented	B-Language
programming	I-Language
.	O
</s>
<s>
For	O
a	O
time	O
,	O
a	O
commercial	O
compiler	B-Language
named	O
CM3	O
maintained	O
by	O
one	O
of	O
the	O
chief	O
implementors	O
prior	O
at	O
DEC	O
SRC	O
who	O
was	O
hired	O
before	O
DEC	O
being	O
sold	O
to	O
Compaq	O
,	O
an	O
integrated	B-Application
development	I-Application
environment	I-Application
(	O
IDE	O
)	O
named	O
Reactor	O
and	O
an	O
extensible	O
Java	B-Language
virtual	I-Language
machine	I-Language
(	O
licensed	O
in	O
binary	O
code	O
and	O
source	O
code	O
formats	O
and	O
buildable	O
with	O
Reactor	O
)	O
were	O
offered	O
by	O
Critical	O
Mass	O
,	O
Inc.	O
,	O
but	O
that	O
company	O
ceased	O
active	O
operations	O
in	O
2000	O
and	O
gave	O
some	O
of	O
the	O
source	O
code	O
of	O
its	O
products	O
to	O
Software	O
Solutions	O
GmbH	O
.	O
</s>
<s>
Modula-3	B-Language
is	O
now	O
taught	O
in	O
universities	O
mostly	O
in	O
comparative	O
programming	O
language	O
courses	O
,	O
and	O
its	O
textbooks	O
are	O
out	O
of	O
print	O
.	O
</s>
<s>
Essentially	O
the	O
only	O
corporate	O
supporter	O
of	O
Modula-3	B-Language
is	O
,	O
which	O
inherited	O
the	O
sources	O
from	O
Critical	O
Mass	O
and	O
has	O
since	O
made	O
several	O
releases	O
of	O
the	O
CM3	O
system	O
in	O
source	O
and	O
binary	O
code	O
.	O
</s>
<s>
The	O
Reactor	O
IDE	O
has	O
been	O
open	B-License
source	I-License
released	O
after	O
several	O
years	O
it	O
had	O
not	O
,	O
with	O
the	O
new	O
name	O
CM3-IDE	O
.	O
</s>
<s>
In	O
March	O
2002	O
,	O
also	O
took	O
over	O
the	O
repository	O
of	O
another	O
active	O
Modula-3	B-Language
distribution	O
,	O
PM3	O
,	O
until	O
then	O
maintained	O
at	O
the	O
École	O
Polytechnique	O
de	O
Montréal	O
but	O
which	O
later	O
continued	O
by	O
the	O
work	O
on	O
HM3	O
improved	O
over	O
the	O
years	O
later	O
until	O
it	O
was	O
obsoleted	O
.	O
</s>
<s>
All	O
programs	O
in	O
Modula-3	B-Language
have	O
at	O
least	O
a	O
module	B-Architecture
file	O
,	O
while	O
most	O
also	O
include	O
an	O
interface	O
file	O
that	O
is	O
used	O
by	O
clients	O
to	O
access	O
data	O
from	O
the	O
module	B-Architecture
.	O
</s>
<s>
As	O
in	O
some	O
other	O
languages	O
,	O
a	O
Modula-3	B-Language
program	O
must	O
export	O
a	O
Main	O
module	B-Architecture
,	O
which	O
can	O
either	O
be	O
a	O
file	O
named	O
Main.m3	O
,	O
or	O
a	O
file	O
can	O
call	O
EXPORT	O
to	O
export	O
the	O
Main	O
module	B-Architecture
.	O
</s>
<s>
Module	B-Architecture
file	O
names	O
are	O
advised	O
to	O
be	O
the	O
same	O
as	O
the	O
name	O
in	O
source	O
code	O
.	O
</s>
<s>
If	O
they	O
differ	O
,	O
the	O
compiler	B-Language
only	O
emits	O
a	O
warning	O
.	O
</s>
<s>
Other	O
conventions	O
in	O
the	O
syntax	O
include	O
naming	O
the	O
exported	O
type	O
of	O
an	O
interface	O
T	O
,	O
since	O
types	O
are	O
usually	O
qualified	O
by	O
their	O
full	O
names	O
,	O
so	O
a	O
type	O
T	O
inside	O
a	O
module	B-Architecture
named	O
Foo	O
will	O
be	O
named	O
Foo.T.	O
</s>
<s>
First	O
and	O
foremost	O
,	O
all	O
compiled	B-Language
units	O
are	O
either	O
INTERFACE	O
or	O
implementation	O
MODULEs	B-Architecture
,	O
of	O
one	O
flavor	O
or	O
another	O
.	O
</s>
<s>
An	O
interface	O
compiled	B-Language
unit	O
,	O
starting	O
with	O
the	O
keyword	O
INTERFACE	O
,	O
defines	O
constants	O
,	O
types	O
,	O
variables	O
,	O
exceptions	B-General_Concept
,	O
and	O
procedures	O
.	O
</s>
<s>
The	O
implementation	O
module	B-Architecture
,	O
starting	O
with	O
the	O
keyword	O
MODULE	B-Architecture
,	O
provides	O
the	O
code	O
,	O
and	O
any	O
further	O
constants	O
,	O
types	O
,	O
or	O
variables	O
needed	O
to	O
implement	O
the	O
interface	O
.	O
</s>
<s>
By	O
default	O
,	O
an	O
implementation	O
module	B-Architecture
will	O
implement	O
the	O
interface	O
of	O
the	O
same	O
name	O
,	O
but	O
a	O
module	B-Architecture
may	O
explicitly	O
EXPORT	O
to	O
a	O
module	B-Architecture
not	O
of	O
the	O
same	O
name	O
.	O
</s>
<s>
For	O
example	O
,	O
the	O
main	O
program	O
exports	O
an	O
implementation	O
module	B-Architecture
for	O
the	O
Main	O
interface	O
.	O
</s>
<s>
Any	O
compiled	B-Language
unit	O
may	O
IMPORT	O
other	O
interfaces	B-Application
,	O
although	O
circular	O
imports	O
are	O
forbidden	O
.	O
</s>
<s>
This	O
may	O
be	O
resolved	O
by	O
doing	O
the	O
import	O
from	O
the	O
implementation	O
MODULE	B-Architecture
.	O
</s>
<s>
The	O
entities	O
within	O
the	O
imported	O
module	B-Architecture
may	O
be	O
imported	O
,	O
instead	O
of	O
only	O
the	O
module	B-Architecture
name	O
,	O
using	O
the	O
FROM	O
Module	B-Architecture
IMPORT	O
Item	O
[	O
,	O
Item ]*	O
syntax	O
:	O
</s>
<s>
A	O
typical	O
use	O
is	O
to	O
define	O
one	O
data	B-General_Concept
structure	I-General_Concept
(	O
record	O
or	O
object	O
)	O
per	O
interface	O
along	O
with	O
any	O
support	O
procedures	O
.	O
</s>
<s>
Some	O
ability	O
is	O
deemed	O
unsafe	O
,	O
where	O
the	O
compiler	B-Language
can	O
no	O
longer	O
guarantee	O
that	O
results	O
will	O
be	O
consistent	O
;	O
for	O
example	O
,	O
when	O
interfacing	O
to	O
the	O
C	B-Language
language	I-Language
.	O
</s>
<s>
The	O
keyword	O
UNSAFE	O
prefixed	O
in	O
front	O
of	O
INTERFACE	O
or	O
MODULE	B-Architecture
,	O
may	O
be	O
used	O
to	O
tell	O
the	O
compiler	B-Language
to	O
enable	O
certain	O
low	O
level	O
features	O
of	O
the	O
language	O
.	O
</s>
<s>
An	O
interface	O
that	O
imports	O
an	O
unsafe	O
module	B-Architecture
must	O
also	O
be	O
unsafe	O
.	O
</s>
<s>
A	O
safe	O
interface	O
may	O
be	O
exported	O
by	O
an	O
unsafe	O
implementation	O
module	B-Architecture
.	O
</s>
<s>
This	O
is	O
the	O
typical	O
use	O
when	O
interfacing	O
to	O
external	O
libraries	B-Library
,	O
where	O
two	O
interfaces	B-Application
are	O
built	O
:	O
one	O
unsafe	O
,	O
the	O
other	O
safe	O
.	O
</s>
<s>
A	O
generic	B-Language
interface	O
and	O
its	O
corresponding	O
generic	B-Language
module	B-Architecture
,	O
</s>
<s>
prefix	O
the	O
INTERFACE	O
or	O
MODULE	B-Architecture
keyword	O
with	O
GENERIC	B-Language
,	O
and	O
take	O
as	O
formal	O
arguments	O
other	O
interfaces	B-Application
.	O
</s>
<s>
Thus	O
(	O
like	O
C++	B-Application
templates	I-Application
)	O
one	O
can	O
easily	O
define	O
and	O
use	O
abstract	O
data	O
types	O
,	O
but	O
unlike	O
C++	B-Language
,	O
the	O
granularity	O
is	O
at	O
the	O
module	B-Architecture
level	O
.	O
</s>
<s>
An	O
interface	O
is	O
passed	O
to	O
the	O
generic	B-Language
interface	O
and	O
implementation	O
modules	B-Architecture
as	O
arguments	O
,	O
and	O
the	O
compiler	B-Language
will	O
generate	O
concrete	O
modules	B-Architecture
.	O
</s>
<s>
For	O
example	O
,	O
one	O
could	O
define	O
a	O
GenericStack	O
,	O
then	O
instantiate	O
it	O
with	O
interfaces	B-Application
such	O
as	O
IntegerElem	O
,	O
or	O
RealElem	O
,	O
or	O
even	O
interfaces	B-Application
to	O
Objects	O
,	O
as	O
long	O
as	O
each	O
of	O
those	O
interfaces	B-Application
defines	O
the	O
properties	O
needed	O
by	O
the	O
generic	B-Language
modules	B-Architecture
.	O
</s>
<s>
The	O
bare	O
types	O
INTEGER	O
,	O
or	O
REAL	O
ca	O
n't	O
be	O
used	O
,	O
because	O
they	O
are	O
not	O
modules	B-Architecture
,	O
and	O
the	O
system	O
of	O
generics	B-Language
is	O
based	O
on	O
using	O
modules	B-Architecture
as	O
arguments	O
.	O
</s>
<s>
By	O
comparison	O
,	O
in	O
a	O
C++	B-Application
template	I-Application
,	O
a	O
bare	O
type	O
would	O
be	O
used	O
.	O
</s>
<s>
A	O
compiled	B-Language
unit	O
must	O
import	O
identifiers	O
from	O
other	O
compiled	B-Language
units	O
,	O
using	O
an	O
IMPORT	O
statement	O
.	O
</s>
<s>
Modula-3	B-Language
supports	O
the	O
allocation	O
of	O
data	O
at	B-Library
runtime	I-Library
.	O
</s>
<s>
There	O
are	O
two	O
kinds	O
of	O
memory	O
that	O
can	O
be	O
allocated	O
,	O
TRACED	O
and	O
UNTRACED	O
,	O
the	O
difference	O
being	O
whether	O
the	O
garbage	B-General_Concept
collector	I-General_Concept
can	O
see	O
it	O
or	O
not	O
.	O
</s>
<s>
In	O
an	O
UNSAFE	O
module	B-Architecture
,	O
DISPOSE	O
is	O
available	O
to	O
free	O
untraced	O
memory	O
.	O
</s>
<s>
Object-oriented	B-Language
programming	I-Language
techniques	O
may	O
be	O
used	O
in	O
Modula-3	B-Language
,	O
but	O
their	O
use	O
is	O
not	O
needed	O
.	O
</s>
<s>
Many	O
of	O
the	O
other	O
features	O
provided	O
in	O
Modula-3	B-Language
(	O
modules	B-Architecture
,	O
generics	B-Language
)	O
can	O
usually	O
take	O
the	O
place	O
of	O
object-orientation	O
.	O
</s>
<s>
An	O
object	O
type	O
(	O
termed	O
a	O
"	O
class	O
"	O
in	O
other	O
object-oriented	B-Language
languages	I-Language
)	O
is	O
introduced	O
with	O
the	O
OBJECT	O
declaration	O
,	O
which	O
has	O
essentially	O
the	O
same	O
syntax	O
as	O
a	O
RECORD	O
declaration	O
,	O
although	O
an	O
object	O
type	O
is	O
a	O
reference	O
type	O
,	O
whereas	O
RECORDs	O
in	O
Modula-3	B-Language
are	O
not	O
(	O
similar	O
to	O
structs	B-Application
in	O
C	B-Language
)	O
.	O
</s>
<s>
Modula-3	B-Language
'	O
s	O
REVEAL	O
construct	O
provides	O
a	O
conceptually	O
simple	O
and	O
clean	O
yet	O
very	O
powerful	O
mechanism	O
for	O
hiding	O
implementation	O
details	O
from	O
clients	O
,	O
with	O
arbitrarily	O
many	O
levels	O
of	O
friendliness	O
.	O
</s>
<s>
Modula-3	B-Language
is	O
one	O
of	O
a	O
few	O
programming	O
languages	O
which	O
requires	O
external	O
references	O
from	O
a	O
module	B-Architecture
to	O
be	O
strictly	O
qualified	O
.	O
</s>
<s>
That	O
is	O
,	O
a	O
reference	O
in	O
module	B-Architecture
A	O
to	O
the	O
object	O
x	O
exported	O
from	O
module	B-Architecture
B	O
must	O
take	O
the	O
form	O
B.x.	O
</s>
<s>
In	O
Modula-3	B-Language
,	O
it	O
is	O
impossible	O
to	O
import	O
all	O
exported	O
names	O
from	O
a	O
module	B-Architecture
.	O
</s>
<s>
Because	O
of	O
the	O
language	O
's	O
requirements	O
on	O
name	O
qualification	O
and	O
method	B-Language
overriding	I-Language
,	O
it	O
is	O
impossible	O
to	O
break	O
a	O
working	O
program	O
simply	O
by	O
adding	O
new	O
declarations	O
to	O
an	O
interface	O
(	O
any	O
interface	O
)	O
.	O
</s>
<s>
This	O
makes	O
it	O
possible	O
for	O
large	O
programs	O
to	O
be	O
edited	O
concurrently	O
by	O
many	O
programmers	O
with	O
no	O
worries	O
about	O
naming	O
conflicts	O
;	O
and	O
it	O
also	O
makes	O
it	O
possible	O
to	O
edit	O
core	O
language	O
libraries	B-Library
with	O
the	O
firm	O
knowledge	O
that	O
no	O
extant	O
program	O
will	O
be	O
broken	O
in	O
the	O
process	O
.	O
</s>
<s>
Exception	B-General_Concept
handling	I-General_Concept
is	O
based	O
on	O
a	O
TRY	O
...	O
EXCEPT	O
block	O
system	O
,	O
which	O
has	O
since	O
become	O
common	O
.	O
</s>
<s>
One	O
feature	O
that	O
has	O
not	O
been	O
adopted	O
in	O
other	O
languages	O
,	O
with	O
the	O
notable	O
exceptions	B-General_Concept
of	O
Delphi	B-Language
,	O
Python	B-Language
,	O
Scala	B-Application
and	O
Visual	B-Language
Basic.NET	I-Language
,	O
is	O
that	O
the	O
EXCEPT	O
construct	O
defined	O
a	O
form	O
of	O
switch	O
statement	O
with	O
each	O
possible	O
exception	O
as	O
a	O
case	O
in	O
its	O
own	O
EXCEPT	O
clause	O
.	O
</s>
<s>
Modula-3	B-Language
also	O
supports	O
a	O
LOOP	O
...	O
EXIT	O
END	O
...	O
construct	O
that	O
loops	O
until	O
an	O
EXIT	O
occurs	O
,	O
a	O
structure	O
equivalent	O
to	O
a	O
simple	O
loop	O
inside	O
a	O
TRY	O
...	O
EXCEPT	O
clause	O
.	O
</s>
<s>
The	O
language	O
supports	O
the	O
use	O
of	O
multi-threading	O
,	O
and	O
synchronization	O
between	O
threads	B-Operating_System
.	O
</s>
<s>
There	O
is	O
a	O
standard	O
module	B-Architecture
within	O
the	O
runtime	B-Library
library	I-Library
(	O
m3core	O
)	O
named	O
Thread	B-Operating_System
,	O
which	O
supports	O
the	O
use	O
of	O
multi-threaded	B-Operating_System
applications	O
.	O
</s>
<s>
The	O
Modula-3	B-Language
runtime	B-Library
may	O
make	O
use	O
of	O
a	O
separate	O
thread	B-Operating_System
for	O
internal	O
tasks	O
such	O
as	O
garbage	B-General_Concept
collection	I-General_Concept
.	O
</s>
<s>
A	O
built-in	O
data	B-General_Concept
structure	I-General_Concept
MUTEX	B-Operating_System
is	O
used	O
to	O
synchronize	O
multiple	O
threads	B-Operating_System
and	O
protect	O
data	B-General_Concept
structures	I-General_Concept
from	O
simultaneous	O
access	O
with	O
possible	O
corruption	O
or	O
race	O
conditions	O
.	O
</s>
<s>
The	O
LOCK	O
statement	O
introduces	O
a	O
block	O
in	O
which	O
the	O
mutex	B-Operating_System
is	O
locked	O
.	O
</s>
<s>
Unlocking	O
a	O
MUTEX	B-Operating_System
is	O
implicit	O
by	O
the	O
code	O
execution	O
locus	O
's	O
leaving	O
the	O
block	O
.	O
</s>
<s>
The	O
MUTEX	B-Operating_System
is	O
an	O
object	O
,	O
and	O
as	O
such	O
,	O
other	O
objects	O
may	O
be	O
derived	O
from	O
it	O
.	O
</s>
<s>
For	O
example	O
,	O
in	O
the	O
input/output	B-General_Concept
(	O
I/O	B-General_Concept
)	O
section	O
of	O
the	O
library	O
libm3	O
,	O
readers	O
and	O
writers	O
(	O
Rd.T	O
,	O
and	O
Wr.T	O
)	O
are	O
derived	O
from	O
MUTEX	B-Operating_System
,	O
and	O
they	O
lock	O
themselves	O
before	O
accessing	O
or	O
modifying	O
any	O
internal	O
data	O
such	O
as	O
buffers	O
.	O
</s>
<s>
Modula-3	B-Language
is	O
one	O
of	O
the	O
rare	O
languages	O
whose	O
evolution	O
of	O
features	O
is	O
documented	O
.	O
</s>
<s>
In	O
Systems	O
Programming	O
with	O
Modula-3	B-Language
,	O
four	O
essential	O
points	O
of	O
the	O
language	O
design	O
are	O
intensively	O
discussed	O
.	O
</s>
<s>
These	O
topics	O
are	O
:	O
structural	O
vs.	O
name	O
equivalence	O
,	O
subtyping	O
rules	O
,	O
generic	B-Language
modules	B-Architecture
,	O
and	O
parameter	O
modes	O
like	O
READONLY	O
.	O
</s>
<s>
Continuing	O
a	O
trend	O
started	O
with	O
the	O
C	B-Language
language	I-Language
,	O
many	O
of	O
the	O
features	O
needed	O
to	O
write	O
real	O
programs	O
were	O
left	O
out	O
of	O
the	O
language	O
definition	O
and	O
instead	O
provided	O
via	O
a	O
standard	B-Library
library	I-Library
set	O
.	O
</s>
<s>
Standard	B-Library
libraries	I-Library
providing	O
the	O
following	O
features	O
.	O
</s>
<s>
These	O
are	O
called	O
standard	O
interfaces	B-Application
and	O
are	O
required	O
(	O
must	O
be	O
provided	O
)	O
in	O
the	O
language	O
.	O
</s>
<s>
Thread	B-Operating_System
:	O
Operations	O
relating	O
to	O
threading	O
,	O
including	O
MUTEX	B-Operating_System
,	O
condition	O
variable	O
,	O
and	O
thread	B-Operating_System
pausing	O
.	O
</s>
<s>
As	O
in	O
C	B-Language
,	O
I/O	B-General_Concept
is	O
also	O
provided	O
via	O
libraries	B-Library
,	O
in	O
Modula-3	B-Language
called	O
Rd	O
and	O
Wr	O
.	O
</s>
<s>
The	O
object-oriented	B-Language
design	O
of	O
the	O
Rd	O
(	O
readers	O
)	O
and	O
Wr	O
(	O
writers	O
)	O
libraries	B-Library
is	O
covered	O
in	O
detail	O
in	O
the	O
book	O
by	O
Greg	O
Nelson	O
.	O
</s>
<s>
An	O
interesting	O
aspect	O
of	O
Modula-3	B-Language
is	O
that	O
it	O
is	O
one	O
of	O
few	O
programming	O
languages	O
which	O
standard	B-Library
libraries	I-Library
have	O
been	O
formally	O
verified	O
not	O
to	O
contain	O
various	O
types	O
of	O
bugs	O
,	O
including	O
locking	B-Operating_System
bugs	O
.	O
</s>
<s>
This	O
was	O
done	O
under	O
the	O
auspices	O
of	O
the	O
Larch/Modula	O
-3	O
(	O
see	O
Larch	B-Language
family	I-Language
)	O
and	O
Extended	B-Application
static	I-Application
checking	I-Application
projects	O
at	O
DEC	O
Systems	O
Research	O
Center	O
.	O
</s>
<s>
Several	O
compilers	B-Language
are	O
available	O
,	O
most	O
of	O
them	O
open	B-License
source	I-License
.	O
</s>
<s>
Olivetti	O
Research	O
Center	O
(	O
ORC	O
)	O
Modula-3	B-Language
toolkit	O
,	O
originally	O
a	O
compiler	B-Language
,	O
now	O
available	O
as	O
a	O
library	O
for	O
syntactic	O
,	O
lexical	B-Language
and	O
semantic	O
analysis	O
of	O
Modula-3	B-Language
programs	O
.	O
</s>
<s>
Since	O
the	O
only	O
aspect	O
of	O
C	B-Language
data	B-General_Concept
structures	I-General_Concept
that	O
is	O
missing	O
from	O
Modula-3	B-Language
is	O
the	O
union	O
type	O
,	O
all	O
extant	O
Modula-3	B-Language
implementations	O
are	O
able	O
to	O
provide	O
good	O
binary	O
code	O
compatibility	O
with	O
C	B-Language
language	I-Language
type	O
declarations	O
of	O
arrays	B-Data_Structure
and	O
structs	B-Application
.	O
</s>
<s>
Greg	O
Nelson	O
,	O
ed.	O
,	O
Systems	O
Programming	O
with	O
Modula-3	B-Language
The	O
definitive	O
reference	O
on	O
the	O
Modula-3	B-Language
language	O
with	O
interesting	O
articles	O
on	O
object-oriented	B-Language
systems	O
software	O
construction	O
and	O
a	O
documentation	O
of	O
the	O
discussion	O
leading	O
to	O
the	O
final	O
features	O
of	O
the	O
language	O
.	O
</s>
<s>
Samuel	O
P	O
.	O
Harbison	O
,	O
Modula-3	B-Language
Easy	O
to	O
use	O
class	O
textbook	O
.	O
</s>
<s>
Renzo	O
Orsini	O
,	O
Agostino	O
Cortesi	O
Programmare	O
in	O
Modula-3	B-Language
:	O
introduzione	O
alla	O
programmazione	O
imperativa	O
e	O
a	O
oggetti	O
an	O
Italian	O
book	O
of	O
the	O
language	O
explaining	O
its	O
main	O
features	O
.	O
</s>
<s>
Software	O
which	O
is	O
programmed	O
Modula-3	B-Language
includes	O
:	O
</s>
<s>
The	O
Obliq	B-Language
language	O
,	O
which	O
uses	O
Modula-3	B-Language
network	O
objects	O
ability	O
to	O
migrate	O
objects	O
over	O
local	O
networks	O
transparently	O
,	O
allowing	O
a	O
distributed	O
ability	O
to	O
Modula-3	B-Language
object-oriented	B-Language
programming	I-Language
paradigm	O
.	O
</s>
<s>
It	O
has	O
been	O
used	O
to	O
build	O
distributed	O
applications	O
,	O
computer	O
animations	O
,	O
and	O
web	O
programming	O
applications	O
in	O
the	O
form	O
of	O
scripting	O
extension	O
to	O
Modula-3	B-Language
.	O
</s>
<s>
Although	O
Modula-3	B-Language
did	O
not	O
gain	O
mainstream	O
status	O
,	O
several	O
parts	O
of	O
the	O
DEC-SRC	O
M3	O
distribution	O
did	O
.	O
</s>
<s>
Probably	O
the	O
most	O
influential	O
part	O
was	O
the	O
Network	O
Objects	O
library	O
,	O
which	O
formed	O
the	O
basis	O
for	O
Java	B-Language
's	O
first	O
Remote	O
Method	O
Invocation	O
(	O
RMI	O
)	O
implementation	O
,	O
including	O
the	O
network	O
protocol	O
.	O
</s>
<s>
Only	O
when	O
Sun	O
moved	O
from	O
the	O
Common	B-Architecture
Object	I-Architecture
Request	I-Architecture
Broker	I-Architecture
Architecture	I-Architecture
(	O
CORBA	B-Architecture
)	O
standard	O
to	O
the	O
IIOP	B-Operating_System
based	I-Operating_System
protocol	I-Operating_System
was	O
it	O
dropped	O
.	O
</s>
<s>
The	O
Java	B-Language
documentation	O
on	O
garbage	B-General_Concept
collection	I-General_Concept
of	O
remote	O
objects	O
still	O
refer	O
to	O
the	O
pioneering	O
work	O
done	O
for	O
Modula-3	B-Language
Network	O
Objects	O
.	O
</s>
<s>
Python	B-Language
's	O
implementation	O
of	O
classes	O
was	O
also	O
inspired	O
by	O
the	O
class	O
mechanism	O
found	O
in	O
C++	B-Language
and	O
Modula-3	B-Language
.	O
</s>
<s>
Also	O
the	O
language	O
Nim	B-Application
makes	O
use	O
of	O
some	O
aspects	O
of	O
Modula-3	B-Language
,	O
such	O
as	O
traced	O
vs	O
untraced	O
pointers	O
.	O
</s>
