<s>
MDL	B-Language
(	O
Model	O
Development	O
Language	O
,	O
or	O
colloquially	O
also	O
referred	O
to	O
as	O
More	O
Datatypes	O
than	O
Lisp	B-Language
or	O
MIT	O
Design	O
Language	O
)	O
is	O
a	O
programming	O
language	O
,	O
a	O
descendant	O
of	O
the	O
language	O
Lisp	B-Language
.	O
</s>
<s>
Its	B-Application
initial	O
purpose	O
was	O
to	O
provide	O
high	O
level	O
language	O
support	O
for	O
the	O
Dynamic	O
Modeling	O
Group	O
at	O
Massachusetts	O
Institute	O
of	O
Technology	O
's	O
(	O
MIT	O
)	O
Project	O
MAC	O
.	O
</s>
<s>
It	O
was	O
developed	O
in	O
1971	O
on	O
a	O
PDP-10	B-Device
running	O
ITS	B-Application
and	O
later	O
ran	O
on	O
TENEX	B-Operating_System
,	O
TOPS-20	B-Operating_System
,	O
BSD	B-Operating_System
,	O
and	O
AEGIS	O
.	O
</s>
<s>
Later	O
,	O
Stu	O
Galley	O
,	O
also	O
of	O
the	O
Dynamic	O
Modeling	O
Group	O
,	O
wrote	O
the	O
MDL	B-Language
documentation	O
.	O
</s>
<s>
MDL	B-Language
was	O
initially	O
called	O
Muddle	O
.	O
</s>
<s>
So	O
the	O
name	O
was	O
sanitized	O
to	O
MDL	B-Language
.	O
</s>
<s>
MDL	B-Language
provides	O
several	O
enhancements	O
to	O
classic	O
Lisp	B-Language
.	O
</s>
<s>
It	O
offers	O
multithreaded	B-Operating_System
expression	O
evaluation	O
and	O
coroutines	B-Architecture
.	O
</s>
<s>
Advanced	O
built-in	O
functions	O
supported	O
interactive	O
debugging	O
of	O
MDL	B-Language
programs	O
,	O
incremental	O
development	O
,	O
and	O
reconstruction	O
of	O
source	O
programs	O
from	O
object	O
programs	O
.	O
</s>
<s>
Although	O
MDL	B-Language
is	O
obsolete	O
,	O
some	O
of	O
its	B-Application
features	O
have	O
been	O
incorporated	O
in	O
later	O
versions	O
of	O
Lisp	B-Language
.	O
</s>
<s>
Gerald	O
Sussman	O
went	O
on	O
to	O
develop	O
the	O
Scheme	B-Language
language	I-Language
,	O
in	O
collaboration	O
with	O
Guy	O
Steele	O
,	O
who	O
later	O
wrote	O
the	O
specifications	O
for	O
Common	B-Language
Lisp	I-Language
and	O
Java	B-Language
.	O
</s>
<s>
Carl	O
Hewitt	O
had	O
already	O
published	O
the	O
idea	O
for	O
the	O
language	O
Planner	B-Application
before	O
the	O
MDL	B-Language
project	O
began	O
,	O
but	O
his	O
subsequent	O
thinking	O
on	O
Planner	B-Application
reflected	O
lessons	O
learned	O
from	O
building	O
MDL	B-Language
.	O
</s>
<s>
Planner	B-Application
concepts	O
influenced	O
languages	O
such	O
as	O
Prolog	B-Language
and	O
Smalltalk	B-Application
.	O
</s>
<s>
Smalltalk	B-Application
and	O
Simula	B-Language
,	O
in	O
turn	O
,	O
influenced	O
Hewitt	O
's	O
future	O
work	O
on	O
the	O
actor	B-Application
model	I-Application
.	O
</s>
<s>
But	O
the	O
largest	O
influence	O
that	O
MDL	B-Language
had	O
was	O
on	O
the	O
software	O
genre	O
of	O
interactive	O
fiction	O
(	O
IF	O
)	O
.	O
</s>
<s>
An	O
IF	O
game	O
named	O
Zork	B-Application
,	O
sometimes	O
called	O
Dungeon	O
,	O
was	O
first	O
written	O
in	O
MDL	B-Language
.	O
</s>
<s>
Later	O
,	O
Reeve	O
,	O
Daniels	O
,	O
Galley	O
and	O
other	O
members	O
of	O
Dynamic	O
Modeling	O
went	O
on	O
to	O
start	O
Infocom	O
,	O
a	O
company	O
that	O
produced	O
many	O
early	O
commercial	B-Application
works	O
of	O
interactive	O
fiction	O
.	O
</s>
<s>
In	O
1980	O
Marc	O
Blank	O
and	O
Joel	O
Berez	O
adapted	O
the	O
MDL	B-Language
language	O
to	O
create	O
a	O
subset	O
called	O
ZIL	O
(	O
Zork	B-Application
Implementation	O
Language	O
)	O
which	O
was	O
used	O
extensively	O
by	O
Infocom	O
to	O
create	O
their	O
award	O
winning	O
games	O
.	O
</s>
<s>
This	O
is	O
a	O
sample	O
of	O
PDP-10	B-Device
MDL	B-Language
:	O
</s>
