<s>
Mesa	O
is	O
a	O
programming	O
language	O
developed	O
in	O
the	O
late	O
1970s	O
at	O
the	O
Xerox	O
Palo	O
Alto	B-Device
Research	O
Center	O
in	O
Palo	O
Alto	B-Device
,	O
California	O
,	O
United	O
States	O
.	O
</s>
<s>
The	O
language	O
name	O
was	O
a	O
pun	O
based	O
upon	O
the	O
programming	O
language	O
catchphrases	O
of	O
the	O
time	O
,	O
because	O
Mesa	O
is	O
a	O
"	B-Language
high	I-Language
level	I-Language
"	I-Language
programming	I-Language
language	I-Language
.	O
</s>
<s>
Mesa	O
is	O
an	O
ALGOL-like	B-Language
language	O
with	O
strong	O
support	O
for	O
modular	B-Architecture
programming	I-Architecture
.	O
</s>
<s>
Every	O
library	O
module	B-Architecture
has	O
at	O
least	O
two	O
source	O
files	O
:	O
a	O
definitions	O
file	O
specifying	O
the	O
library	O
's	O
interface	B-Application
plus	O
one	O
or	O
more	O
program	O
files	O
specifying	O
the	O
implementation	O
of	O
the	O
procedures	O
in	O
the	O
interface	B-Application
.	O
</s>
<s>
Mesa	O
introduced	O
several	O
other	O
innovations	O
in	O
language	O
design	O
and	O
implementation	O
,	O
notably	O
in	O
the	O
handling	O
of	O
software	O
exceptions	O
,	O
thread	B-Operating_System
synchronization	O
,	O
and	O
incremental	B-Application
compilation	I-Application
.	O
</s>
<s>
Mesa	O
was	O
developed	O
on	O
the	O
Xerox	B-Device
Alto	I-Device
,	O
one	O
of	O
the	O
first	O
personal	B-Device
computers	I-Device
with	O
a	O
graphical	B-Application
user	I-Application
interface	I-Application
,	O
however	O
,	O
most	O
of	O
the	O
Alto	B-Device
's	O
system	O
software	O
was	O
written	O
in	O
BCPL	B-Language
.	O
</s>
<s>
Mesa	O
was	O
the	O
system	O
programming	O
language	O
of	O
the	O
later	O
Xerox	B-Operating_System
Star	I-Operating_System
workstations	O
,	O
and	O
for	O
the	O
GlobalView	O
desktop	O
environment	O
.	O
</s>
<s>
Xerox	O
PARC	O
later	O
developed	O
Cedar	B-Language
,	O
which	O
was	O
a	O
superset	O
of	O
Mesa	O
.	O
</s>
<s>
Mesa	O
and	O
Cedar	B-Language
had	O
a	O
major	O
influence	O
on	O
the	O
design	O
of	O
other	O
important	O
languages	O
,	O
such	O
as	O
Modula-2	B-Language
and	O
Java	B-Language
,	O
and	O
was	O
an	O
important	O
vehicle	O
for	O
the	O
development	O
and	O
dissemination	O
of	O
the	O
fundamentals	O
of	O
GUIs	B-Application
,	O
networked	O
environments	O
,	O
and	O
the	O
other	O
advances	O
Xerox	O
contributed	O
to	O
the	O
field	O
of	O
computer	B-General_Concept
science	I-General_Concept
.	O
</s>
<s>
Mesa	O
was	O
originally	O
designed	O
in	O
the	O
Computer	O
Systems	O
Laboratory	O
(	O
CSL	O
)	O
,	O
a	O
branch	O
of	O
the	O
Xerox	O
Palo	O
Alto	B-Device
Research	O
Center	O
,	O
for	O
the	O
Alto	B-Device
,	O
an	O
experimental	O
micro-coded	O
workstation	O
.	O
</s>
<s>
Initially	O
,	O
its	O
spread	O
was	O
confined	O
to	O
PARC	O
and	O
a	O
few	O
universities	O
to	O
which	O
Xerox	O
had	O
donated	O
some	O
Altos	B-Device
.	O
</s>
<s>
Mesa	O
was	O
later	O
adopted	O
as	O
the	O
systems	O
programming	O
language	O
for	O
Xerox	O
's	O
commercial	O
workstations	O
such	O
as	O
the	O
Xerox	B-Operating_System
8010	I-Operating_System
(	O
Xerox	B-Operating_System
Star	I-Operating_System
,	O
Dandelion	O
)	O
and	O
Xerox	B-Device
6085	I-Device
(	O
Daybreak	O
)	O
,	O
in	O
particular	O
for	O
the	O
Pilot	B-Application
operating	I-Application
system	I-Application
.	O
</s>
<s>
A	O
secondary	O
development	O
environment	O
,	O
called	O
the	O
Xerox	B-Application
Development	I-Application
Environment	I-Application
(	O
XDE	O
)	O
allowed	O
developers	O
to	O
debug	O
both	O
the	O
operating	O
system	O
Pilot	O
as	O
well	O
as	O
ViewPoint	O
GUI	B-Application
applications	O
using	O
a	O
world	O
swap	O
mechanism	O
.	O
</s>
<s>
This	O
technique	O
did	O
not	O
scale	O
very	O
well	O
to	O
large	O
application	O
images	O
(	O
several	O
megabytes	O
)	O
,	O
and	O
so	O
the	O
Pilot/Mesa	O
world	O
in	O
later	O
releases	O
moved	O
away	O
from	O
the	O
world	O
swap	O
view	O
when	O
the	O
micro-coded	O
machines	O
were	O
phased	O
out	O
in	O
favor	O
of	O
SPARC	O
workstations	O
and	O
Intel	O
PCs	B-Device
running	O
a	O
Mesa	O
PrincOps	O
emulator	O
for	O
the	O
basic	O
hardware	O
instruction	O
set	O
.	O
</s>
<s>
Mesa	O
was	O
compiled	O
into	O
a	O
stack-machine	O
language	O
,	O
purportedly	O
with	O
the	O
highest	O
code	O
density	O
ever	O
achieved	O
(	O
roughly	O
4	O
bytes	O
per	O
high-level	B-Language
language	I-Language
statement	O
)	O
.	O
</s>
<s>
Trained	O
Mesa	O
programmers	O
from	O
Xerox	O
were	O
well	O
versed	O
in	O
the	O
fundamental	O
of	O
GUIs	B-Application
,	O
networking	O
,	O
exceptions	O
,	O
and	O
multi-threaded	B-Operating_System
programming	I-Operating_System
,	O
almost	O
a	O
decade	O
before	O
they	O
became	O
standard	O
tools	O
of	O
the	O
trade	O
.	O
</s>
<s>
Within	O
Xerox	O
,	O
Mesa	O
was	O
eventually	O
superseded	O
by	O
the	O
Cedar	B-Language
programming	O
language	O
.	O
</s>
<s>
Many	O
Mesa	O
programmers	O
and	O
developers	O
left	O
Xerox	O
in	O
1985	O
;	O
some	O
of	O
them	O
went	O
to	O
DEC	O
Systems	O
Research	O
Center	O
where	O
they	O
used	O
their	O
experience	O
with	O
Mesa	O
in	O
the	O
design	O
of	O
Modula-2	B-Language
+	I-Language
,	O
and	O
later	O
of	O
Modula-3	B-Language
.	O
</s>
<s>
Mesa	O
was	O
a	O
strongly	O
typed	O
programming	O
language	O
with	O
type-checking	O
across	O
module	B-Architecture
boundaries	O
,	O
but	O
with	O
enough	O
flexibility	O
in	O
its	O
type	O
system	O
that	O
heap	O
allocators	O
could	O
be	O
written	O
in	O
Mesa	O
.	O
</s>
<s>
Due	O
to	O
its	O
strict	O
separation	O
between	O
interface	B-Application
and	O
implementation	O
,	O
Mesa	O
allows	O
true	O
incremental	B-Application
compilation	I-Application
and	O
encourages	O
architecture	B-General_Concept
-	O
and	O
platform-independent	O
programming	O
.	O
</s>
<s>
They	O
also	O
simplified	O
source-level	O
debugging	B-Application
,	O
including	O
remote	O
debugging	B-Application
via	O
the	O
Ethernet	O
.	O
</s>
<s>
Mesa	O
had	O
rich	O
exception	B-General_Concept
handling	I-General_Concept
facilities	O
,	O
with	O
four	O
types	O
of	O
exceptions	O
.	O
</s>
<s>
It	O
had	O
support	O
for	O
thread	B-Operating_System
synchronization	O
via	O
monitors	O
.	O
</s>
<s>
Mesa	O
was	O
the	O
first	O
language	O
to	O
implement	O
monitor	O
BROADCAST	O
,	O
a	O
concept	O
introduced	O
by	O
the	O
Pilot	B-Application
operating	I-Application
system	I-Application
.	O
</s>
<s>
Mesa	O
has	O
an	O
"	O
imperative	O
"	O
and	O
"	O
algebraic	O
"	O
syntax	B-Application
,	O
based	O
on	O
ALGOL	B-Language
and	O
Pascal	B-Application
rather	O
than	O
on	O
BCPL	B-Language
or	O
C	B-Language
;	O
for	O
instance	O
,	O
compound	O
commands	O
are	O
indicated	O
by	O
the	O
and	O
keywords	O
rather	O
than	O
braces	O
.	O
</s>
<s>
Due	O
to	O
PARC	O
's	O
using	O
the	O
1963	O
variant	O
of	O
ASCII	B-Protocol
rather	O
than	O
the	O
more	O
common	O
1967	O
variant	O
,	O
the	O
Alto	B-Device
's	O
character	O
set	O
included	O
a	O
left-pointing	O
arrow	O
(	O
←	O
)	O
rather	O
than	O
an	O
underscore	O
.	O
</s>
<s>
The	O
result	O
of	O
this	O
is	O
that	O
Alto	B-Device
programmers	O
(	O
including	O
those	O
using	O
Mesa	O
,	O
Smalltalk	O
etc	O
.	O
)	O
</s>
<s>
On	O
the	O
other	O
hand	O
,	O
the	O
availability	O
of	O
the	O
left-pointing	O
arrow	O
allowed	O
them	O
to	O
use	O
it	O
for	O
the	O
assignment	O
operator	O
,	O
as	O
it	O
originally	O
had	O
been	O
in	O
ALGOL	B-Language
.	O
</s>
<s>
graduate	O
from	O
Colorado	O
who	O
had	O
written	O
his	O
thesis	O
on	O
exception	B-General_Concept
handling	I-General_Concept
facilities	O
in	O
algorithmic	B-Language
languages	I-Language
.	O
</s>
<s>
As	O
the	O
language	O
did	O
not	O
have	O
type-safe	B-Language
checks	O
to	O
verify	O
full	O
coverage	O
for	O
signal	O
handling	O
,	O
uncaught	O
exceptions	O
were	O
a	O
common	O
cause	O
of	O
bugs	O
in	O
released	O
software	O
.	O
</s>
<s>
Mesa	O
was	O
the	O
precursor	O
to	O
the	O
programming	O
language	O
Cedar	B-Language
.	O
</s>
<s>
Cedar	B-Language
's	O
main	O
additions	O
were	O
garbage	B-General_Concept
collection	I-General_Concept
,	O
dynamic	O
types	O
,	O
better	O
string	O
support	O
through	O
ropes	B-Data_Structure
,	O
a	O
limited	O
form	O
of	O
type	B-Application
parameterization	I-Application
,	O
and	O
special	O
syntax	B-Application
for	O
identifying	O
the	O
type-safe	B-Language
parts	O
of	O
multi-module	O
software	B-Architecture
packages	I-Architecture
,	O
to	O
ensure	O
deterministic	O
execution	O
and	O
prevent	O
memory	B-Error_Name
leaks	I-Error_Name
.	O
</s>
<s>
The	O
United	O
States	O
Department	O
of	O
Defense	O
approached	O
Xerox	O
to	O
use	O
Mesa	O
for	O
its	O
"	O
IronMan	O
"	O
programming	O
language	O
(	O
see	O
Steelman	B-Language
language	I-Language
requirements	I-Language
)	O
,	O
but	O
Xerox	O
declined	O
due	O
to	O
conflicting	O
goals	O
.	O
</s>
<s>
The	O
Department	O
of	O
Defense	O
instead	O
eventually	O
chose	O
and	O
developed	O
the	O
Ada	B-Language
programming	I-Language
language	I-Language
from	O
the	O
candidates	O
.	O
</s>
<s>
The	O
original	O
Star	O
Desktop	O
evolved	O
into	O
the	O
ViewPoint	O
Desktop	O
and	O
later	O
became	O
GlobalView	O
which	O
was	O
ported	O
to	O
various	O
Unix	O
platforms	B-Device
,	O
such	O
as	O
SunOS	B-Application
Unix	I-Application
and	O
AIX	B-Application
.	O
</s>
<s>
A	O
Mesa	O
to	O
C	B-Language
compiler	O
was	O
written	O
and	O
the	O
resulting	O
code	O
compiled	O
for	O
the	O
target	O
platform	B-Device
.	O
</s>
<s>
In	O
1976	O
,	O
during	O
a	O
sabbatical	O
at	O
Xerox	O
PARC	O
,	O
Niklaus	O
Wirth	O
became	O
acquainted	O
with	O
Mesa	O
,	O
which	O
had	O
a	O
major	O
influence	O
in	O
the	O
design	O
of	O
his	O
Modula-2	B-Language
language	I-Language
.	O
</s>
<s>
Java	B-Language
explicitly	O
refers	O
to	O
Mesa	O
as	O
a	O
predecessor	O
.	O
</s>
