<s>
TUTOR	B-Language
,	O
also	O
known	O
as	O
PLATO	B-Operating_System
Author	O
Language	O
,	O
is	O
a	O
programming	O
language	O
developed	O
for	O
use	O
on	O
the	O
PLATO	B-Operating_System
system	I-Operating_System
at	O
the	O
University	O
of	O
Illinois	O
at	O
Urbana-Champaign	O
beginning	O
in	O
roughly	O
1965	O
.	O
</s>
<s>
TUTOR	B-Language
was	O
initially	O
designed	O
by	O
Paul	O
Tenczar	O
for	O
use	O
in	O
computer	O
assisted	O
instruction	O
(	O
CAI	O
)	O
and	O
computer	O
managed	O
instruction	O
(	O
CMI	O
)	O
(	O
in	O
computer	O
programs	O
called	O
"	O
lessons	O
"	O
)	O
and	O
has	O
many	O
features	O
for	O
that	O
purpose	O
.	O
</s>
<s>
For	O
example	O
,	O
TUTOR	B-Language
has	O
powerful	O
answer-parsing	O
and	O
answer-judging	O
commands	O
,	O
graphics	O
,	O
and	O
features	O
to	O
simplify	O
handling	O
student	O
records	O
and	O
statistics	O
by	O
instructors	O
.	O
</s>
<s>
TUTOR	B-Language
's	O
flexibility	O
,	O
in	O
combination	O
with	O
PLATO	B-Operating_System
's	O
computational	O
power	O
(	O
running	O
on	O
what	O
was	O
considered	O
a	O
supercomputer	O
in	O
1972	O
)	O
,	O
also	O
made	O
it	O
suitable	O
for	O
the	O
creation	O
of	O
games	O
—	O
including	O
flight	O
simulators	O
,	O
war	O
games	O
,	O
dungeon	O
style	O
multiplayer	O
role-playing	O
games	O
,	O
card	O
games	O
,	O
word	O
games	O
,	O
and	O
medical	O
lesson	O
games	O
such	O
as	O
Bugs	O
and	O
Drugs	O
(	O
BND	O
)	O
.	O
</s>
<s>
TUTOR	B-Language
lives	O
on	O
today	O
as	O
the	O
programming	O
language	O
for	O
the	O
Cyber1	O
PLATO	B-Operating_System
System	I-Operating_System
,	O
which	O
runs	O
most	O
of	O
the	O
source	O
code	O
from	O
1980s	O
PLATO	B-Operating_System
and	O
has	O
roughly	O
5000	O
users	O
as	O
of	O
June	O
2020	O
.	O
</s>
<s>
TUTOR	B-Language
was	O
originally	O
developed	O
as	O
a	O
special	O
purpose	O
authoring	O
language	O
for	O
designing	O
instructional	O
lessons	O
,	O
and	O
its	O
evolution	O
into	O
a	O
general	O
purpose	O
programming	O
language	O
was	O
unplanned	O
.	O
</s>
<s>
The	O
name	O
TUTOR	B-Language
was	O
first	O
applied	O
to	O
the	O
authoring	O
language	O
of	O
the	O
PLATO	B-Operating_System
system	I-Operating_System
in	O
the	O
later	O
days	O
of	O
Plato	B-Operating_System
III	I-Operating_System
.	O
</s>
<s>
The	O
first	O
documentation	O
of	O
the	O
language	O
,	O
under	O
this	O
name	O
,	O
appears	O
to	O
have	O
been	O
The	O
TUTOR	B-Language
Manual	O
,	O
CERL	O
Report	O
X-4	O
,	O
by	O
R	O
.	O
A	O
.	O
Avner	O
and	O
P	O
.	O
Tenczar	O
,	O
Jan	O
.	O
1969	O
.	O
</s>
<s>
The	O
article	O
Teaching	O
the	O
Translation	O
of	O
Russian	O
by	O
Computer	O
gives	O
a	O
snapshot	O
of	O
TUTOR	B-Language
from	O
shortly	O
before	O
PLATO	B-Operating_System
IV	I-Operating_System
was	O
operational	O
.	O
</s>
<s>
Through	O
the	O
1970s	O
,	O
the	O
developers	O
of	O
TUTOR	B-Language
took	O
advantage	O
of	O
the	O
fact	O
that	O
the	O
entire	O
corpus	O
of	O
TUTOR	B-Language
programs	O
were	O
stored	O
on-line	O
on	O
the	O
same	O
computer	O
system	O
.	O
</s>
<s>
Whenever	O
they	O
felt	O
a	O
need	O
to	O
change	O
the	O
language	O
,	O
they	O
ran	O
conversion	O
software	O
over	O
the	O
corpus	O
of	O
TUTOR	B-Language
code	O
to	O
revise	O
all	O
existing	O
code	O
so	O
that	O
it	O
conformed	O
with	O
the	O
changes	O
they	O
had	O
made	O
.	O
</s>
<s>
As	O
a	O
result	O
,	O
once	O
new	O
versions	O
of	O
TUTOR	B-Language
were	O
developed	O
,	O
maintaining	O
compatibility	O
with	O
the	O
PLATO	B-Operating_System
version	O
could	O
be	O
very	O
difficult	O
.	O
</s>
<s>
Control	O
Data	O
Corporation	O
(	O
CDC	O
)	O
,	O
by	O
1981	O
,	O
had	O
largely	O
expunged	O
the	O
name	O
TUTOR	B-Language
from	O
their	O
PLATO	B-Operating_System
documentation	O
.	O
</s>
<s>
They	O
referred	O
to	O
the	O
language	O
itself	O
as	O
the	O
PLATO	B-Operating_System
Author	O
Language	O
.	O
</s>
<s>
The	O
phrase	O
TUTOR	B-Language
file	O
or	O
even	O
TUTOR	B-Language
lesson	O
file	O
survived	O
,	O
however	O
,	O
as	O
the	O
name	O
of	O
the	O
type	O
of	O
file	O
used	O
to	O
store	O
text	O
written	O
in	O
the	O
PLATO	B-Operating_System
Author	O
Language	O
.	O
</s>
<s>
A	O
TUTOR	B-Language
lesson	O
consists	O
of	O
a	O
sequence	O
of	O
units	O
where	O
each	O
unit	O
begins	O
with	O
the	O
presentation	O
of	O
information	O
and	O
progress	O
from	O
one	O
unit	O
to	O
the	O
next	O
is	O
contingent	O
on	O
correctly	O
answering	O
one	O
or	O
more	O
questions	O
.	O
</s>
<s>
As	O
with	O
COBOL	B-Application
paragraphs	O
,	O
control	O
may	O
enter	O
a	O
TUTOR	B-Language
unit	O
from	O
the	O
preceding	O
unit	O
and	O
exit	O
into	O
the	O
next	O
,	O
but	O
units	O
are	O
also	O
callable	O
as	O
subroutines	O
using	O
the	O
do	O
or	O
join	O
commands	O
.	O
</s>
<s>
Here	O
is	O
an	O
example	O
unit	O
from	O
page	O
5	O
of	O
the	O
TUTOR	B-Language
User	O
's	O
Memo	O
,	O
March	O
1973	O
(	O
Computer-based	B-Operating_System
Education	I-Operating_System
Research	I-Operating_System
Laboratory	I-Operating_System
,	O
University	O
of	O
Illinois	O
at	O
Urbana-Champaign	O
)	O
:	O
</s>
<s>
First	O
,	O
TUTOR	B-Language
is	O
a	O
fixed	O
format	O
language	O
.	O
</s>
<s>
Although	O
a	O
tab	O
key	O
was	O
be	O
used	O
to	O
get	O
to	O
the	O
9th	O
column	O
,	O
it	O
generated	O
spaces	O
as	O
plato	B-Operating_System
had	O
no	O
tab	O
character	O
.	O
</s>
<s>
The	O
arrow	O
command	O
marks	O
the	O
entrance	O
to	O
a	O
judging	O
block	O
This	O
control	O
structure	O
is	O
one	O
of	O
TUTOR	B-Language
's	O
unique	O
features	O
.	O
</s>
<s>
TUTOR	B-Language
contained	O
a	O
number	O
of	O
unique	O
features	O
.	O
</s>
<s>
The	O
following	O
list	O
is	O
not	O
intended	O
as	O
a	O
substitute	O
for	O
a	O
TUTOR	B-Language
manual	O
,	O
but	O
merely	O
highlights	O
the	O
most	O
interesting	O
,	O
innovative	O
,	O
and	O
sometimes	O
confusing	O
features	O
of	O
the	O
language	O
.	O
</s>
<s>
A	O
judging	O
block	O
in	O
TUTOR	B-Language
is	O
a	O
control	O
structure	O
that	O
begins	O
with	O
an	O
arrow	O
command	O
and	O
ends	O
with	O
the	O
next	O
arrow	O
,	O
endarrow	O
or	O
unit	O
command	O
.	O
</s>
<s>
Each	O
judging	O
block	O
consists	O
of	O
a	O
sequence	O
of	O
pattern	B-Language
matching	I-Language
commands	O
,	O
each	O
of	O
which	O
introduces	O
a	O
(	O
possibly	O
empty	O
)	O
block	O
of	O
commands	O
to	O
be	O
executed	O
if	O
that	O
pattern	B-Language
matches	I-Language
.	O
</s>
<s>
The	O
two	O
most	O
common	O
pattern	B-Language
matching	I-Language
commands	O
were	O
answer	O
and	O
wrong	O
.	O
</s>
<s>
These	O
had	O
identical	O
pattern	B-Language
matching	I-Language
semantics	O
except	O
that	O
answer	O
judged	O
a	O
student	O
response	O
to	O
be	O
correct	O
if	O
it	O
matched	O
,	O
while	O
wrong	O
judged	O
a	O
student	O
response	O
to	O
be	O
incorrect	O
.	O
</s>
<s>
consider	O
this	O
example	O
from	O
exercise	O
4-1	O
in	O
the	O
1973	O
TUTOR	B-Language
User	O
's	O
Memo	O
:	O
</s>
<s>
The	O
pattern	B-Language
matching	I-Language
subsystem	O
recognized	O
spelling	O
errors	O
,	O
so	O
the	O
words	O
"	O
triangel	O
"	O
or	O
"	O
triangl	O
"	O
would	O
match	O
the	O
example	O
pattern	O
.	O
</s>
<s>
The	O
pattern	B-Language
matching	I-Language
algorithms	O
used	O
by	O
various	O
TUTOR	B-Language
implementations	O
varied	O
in	O
detail	O
,	O
but	O
typically	O
,	O
each	O
word	O
in	O
the	O
input	O
text	O
and	O
each	O
word	O
in	O
the	O
pattern	O
were	O
converted	O
to	O
bit	B-Data_Structure
vectors	I-Data_Structure
.	O
</s>
<s>
To	O
see	O
whether	O
a	O
word	O
of	O
student	O
input	O
matched	O
a	O
word	O
of	O
the	O
pattern	O
,	O
the	O
Hamming	O
distance	O
between	O
the	O
two	O
bit	B-Data_Structure
vectors	I-Data_Structure
was	O
used	O
as	O
a	O
measure	O
of	O
the	O
degree	O
of	O
difference	O
between	O
the	O
words	O
.	O
</s>
<s>
Bit	B-Data_Structure
vectors	I-Data_Structure
were	O
typically	O
60	O
or	O
64	O
bits	O
long	O
,	O
with	O
fields	O
for	O
letter	O
presence	O
,	O
letter	O
pair	O
presence	O
,	O
and	O
the	O
first	O
letter	O
.	O
</s>
<s>
As	O
a	O
result	O
,	O
the	O
number	O
of	O
one	O
bits	O
in	O
the	O
exclusive	O
or	O
of	O
two	O
such	O
bit	B-Data_Structure
vectors	I-Data_Structure
approximated	O
the	O
extent	O
of	O
the	O
phonetic	O
difference	O
between	O
the	O
corresponding	O
words	O
.	O
</s>
<s>
All	O
early	O
presentations	O
of	O
the	O
control	O
structure	O
of	O
a	O
TUTOR	B-Language
judging	O
block	O
were	O
confusing	O
.	O
</s>
<s>
of	O
this	O
control	O
structure	O
consists	O
of	O
a	O
series	O
of	O
cases	O
,	O
each	O
introduced	O
by	O
a	O
pattern	B-Language
matching	I-Language
command	O
such	O
as	O
answer	O
or	O
wrong	O
.	O
</s>
<s>
Consider	O
this	O
example	O
,	O
from	O
exercise	O
4-1	O
of	O
the	O
1973	O
TUTOR	B-Language
User	O
's	O
Memo	O
:	O
</s>
<s>
It	O
was	O
defined	O
as	O
being	O
equivalent	O
to	O
textual	O
substitution	O
of	O
the	O
body	O
of	O
the	O
joined	O
unit	O
in	O
place	O
of	O
the	O
join	O
command	O
itself	O
(	O
page	O
21	O
,	O
1973	O
TUTOR	B-Language
User	O
's	O
Memo	O
)	O
.	O
</s>
<s>
The	O
PLATO	B-Operating_System
IV	I-Operating_System
student	O
terminal	O
had	O
a	O
512	O
by	O
512	O
pixel	B-Algorithm
plasma	O
display	O
panel	O
,	O
</s>
<s>
Each	O
pixel	B-Algorithm
on	O
the	O
PLATO	B-Operating_System
IV	I-Operating_System
terminal	O
was	O
either	O
orange	O
or	O
black	O
.	O
</s>
<s>
The	O
CDC	O
PLATO	B-Operating_System
V	I-Operating_System
terminal	O
used	O
a	O
monochrome	O
black	O
and	O
white	O
CRT	B-Device
to	O
emulate	O
the	O
plasma	O
panel	O
.	O
</s>
<s>
The	O
built-in	O
character	O
set	O
had	O
4	O
sets	O
of	O
63	O
characters	O
,	O
each	O
8	O
by	O
16	O
pixels	B-Algorithm
,	O
half	O
of	O
these	O
were	O
fixed	O
,	O
half	O
were	O
programmable	O
.	O
</s>
<s>
The	O
Tutor	B-Language
language	O
provided	O
complete	O
support	O
for	O
this	O
terminal	O
.	O
</s>
<s>
There	O
were	O
two	O
coordinate	O
systems	O
(	O
see	O
page	O
II-1	O
of	O
The	O
TUTOR	B-Language
Language	O
by	O
Bruce	O
Sherwood	O
)	O
:	O
</s>
<s>
The	O
fine	O
coordinate	O
0,511	O
specified	O
the	O
upper	O
left	O
corner	O
of	O
the	O
screen	O
,	O
while	O
0,496	O
was	O
equivalent	O
to	O
the	O
coarse	O
101	O
,	O
allowing	O
for	O
the	O
16	O
pixel	B-Algorithm
height	O
of	O
a	O
character	O
and	O
the	O
fact	O
that	O
characters	O
were	O
plotted	O
relative	O
to	O
their	O
lower	O
left	O
corner	O
.	O
</s>
<s>
The	O
following	O
example	O
illustrates	O
some	O
of	O
Tutor	B-Language
's	O
drawing	O
commands	O
.	O
</s>
<s>
Hand	O
composing	O
draw	O
commands	O
is	O
difficult	O
,	O
so	O
a	O
picture	O
editor	O
was	O
included	O
in	O
the	O
PLATO	B-Operating_System
system	I-Operating_System
by	O
1974	O
to	O
automate	O
this	O
work	O
.	O
</s>
<s>
The	O
following	O
example	O
illustrates	O
some	O
of	O
the	O
text	O
rendering	O
tools	O
of	O
Tutor	B-Language
.	O
</s>
<s>
Text	O
rendered	O
in	O
size	O
zero	O
rotation	O
zero	O
used	O
the	O
built-in	O
character	O
rendering	O
hardware	O
of	O
the	O
PLATO	B-Operating_System
terminal	O
,	O
while	O
rendering	O
with	O
nonzero	O
size	O
and	O
rotation	O
was	O
done	O
with	O
line	O
segments	O
and	O
therefore	O
significantly	O
slower	O
due	O
to	O
the	O
speed	O
of	O
the	O
communication	O
link	O
to	O
the	O
terminal	O
.	O
</s>
<s>
Aside	O
from	O
its	O
unique	O
answer	O
judging	O
mechanisms	O
,	O
TUTOR	B-Language
's	O
original	O
set	O
of	O
control	O
structures	O
was	O
rather	O
sparse	O
.	O
</s>
<s>
The	O
semantics	O
of	O
these	O
control	O
structures	O
was	O
routine	O
,	O
but	O
the	O
syntax	O
inherited	O
the	O
mandatory	O
indentation	O
of	O
the	O
Tutor	B-Language
Language	O
,	O
presaging	O
that	O
of	O
Python	B-Language
and	O
adding	O
a	O
unique	O
nonblank	O
indent	O
character	O
to	O
distinguish	O
indenting	O
from	O
continuation	O
lines	O
.	O
</s>
<s>
This	O
is	O
illustrated	O
in	O
the	O
following	O
example	O
,	O
from	O
page	O
S5	O
of	O
the	O
Summary	O
of	O
TUTOR	B-Language
Commands	O
and	O
System	O
Variables	O
(	O
10th	O
ed	O
)	O
by	O
Elaine	O
Avner	O
,	O
1981	O
:	O
</s>
<s>
It	O
had	O
a	O
dedicated	O
key	O
on	O
the	O
PLATO	B-Operating_System
IV	I-Operating_System
keyboard	O
.	O
)	O
</s>
<s>
This	O
is	O
illustrated	O
in	O
the	O
following	O
example	O
,	O
from	O
page	O
S6	O
of	O
the	O
Summary	O
of	O
TUTOR	B-Language
Commands	O
and	O
System	O
Variables	O
(	O
10th	O
ed	O
)	O
by	O
Elaine	O
Avner	O
,	O
1981	O
:	O
</s>
<s>
Note	O
that	O
the	O
reloop	O
and	O
outloop	O
commands	O
are	O
somewhat	O
analogous	O
to	O
the	O
continue	O
and	O
break	O
statements	O
of	O
languages	O
based	O
on	O
C	B-Language
,	O
except	O
that	O
they	O
must	O
sit	O
at	O
the	O
indenting	O
level	O
of	O
the	O
loop	O
they	O
modify	O
,	O
and	O
they	O
have	O
a	O
condition	O
tag	O
that	O
indicates	O
when	O
the	O
indicated	O
control	O
transfer	O
is	O
to	O
take	O
place	O
.	O
</s>
<s>
TUTOR	B-Language
's	O
expression	O
syntax	O
did	O
not	O
look	O
back	O
to	O
the	O
syntax	O
of	O
FORTRAN	B-Application
,	O
nor	O
was	O
it	O
limited	O
by	O
poorly	O
designed	O
character	O
sets	O
of	O
the	O
era	O
.	O
</s>
<s>
For	O
example	O
,	O
the	O
PLATO	B-Operating_System
IV	I-Operating_System
character	O
set	O
included	O
control	O
characters	O
for	O
subscript	O
and	O
superscript	O
,	O
and	O
TUTOR	B-Language
used	O
these	O
for	O
exponentiation	O
.	O
</s>
<s>
Consider	O
this	O
command	O
(	O
from	O
page	O
IV-1	O
of	O
The	O
TUTOR	B-Language
Language	O
,	O
Sherwood	O
,	O
1974	O
)	O
:	O
</s>
<s>
The	O
character	O
set	O
also	O
included	O
the	O
conventional	O
symbols	O
for	O
multiplication	O
and	O
division	O
,	O
×	O
and	O
÷	O
,	O
but	O
in	O
a	O
more	O
radical	O
departure	O
from	O
the	O
conventions	O
established	O
by	O
FORTRAN	B-Application
,	O
it	O
allowed	O
implicit	O
multiplication	O
,	O
so	O
the	O
expressions	O
(	O
4+7	O
)	O
(	O
3+6	O
)	O
and	O
3.4	O
+	O
5(23-3 )	O
/2	O
were	O
valid	O
,	O
with	O
the	O
values	O
99	O
and	O
15.9	O
,	O
respectively	O
(	O
op	O
cit	O
)	O
.	O
</s>
<s>
When	O
students	O
typed	O
in	O
a	O
numeric	O
answer	O
to	O
a	O
question	O
,	O
they	O
could	O
use	O
operators	O
and	O
variables	O
and	O
standard	O
algebraic	O
notation	O
,	O
and	O
the	O
program	O
would	O
use	O
the	O
TUTOR	B-Language
"	O
compute	O
"	O
command	O
to	O
compile	O
and	O
run	O
the	O
formula	O
and	O
check	O
that	O
it	O
was	O
numerically	O
equivalent	O
(	O
or	O
within	O
the	O
floating	O
point	O
roundoff	O
error	O
)	O
to	O
the	O
correct	O
answer	O
.	O
</s>
<s>
In	O
TUTOR	B-Language
,	O
the	O
floating-point	O
comparison	O
x	O
=	O
y	O
was	O
defined	O
as	O
being	O
true	O
if	O
x	O
and	O
y	O
were	O
approximately	O
equal	O
(	O
see	O
page	O
C5	O
of	O
PLATO	B-Operating_System
User	O
's	O
Memo	O
,	O
Number	O
One	O
by	O
Avner	O
,	O
1975	O
)	O
.	O
</s>
<s>
As	O
an	O
authoring	O
language	O
,	O
TUTOR	B-Language
began	O
with	O
only	O
minimal	O
memory	O
resources	O
and	O
only	O
the	O
crudest	O
tools	O
for	O
manipulating	O
them	O
.	O
</s>
<s>
Each	O
user	O
process	O
had	O
a	O
private	O
data	O
segment	O
of	O
150	O
variables	O
,	O
and	O
shared	O
common	B-Application
blocks	I-Application
could	O
be	O
attached	O
,	O
allowing	O
inter-user	O
communication	O
through	O
shared	O
memory	O
.	O
</s>
<s>
On	O
the	O
PLATO	B-Operating_System
IV	I-Operating_System
system	O
,	O
words	O
were	O
60	O
bits	O
,	O
in	O
keeping	O
with	O
the	O
CDC	B-Device
6600	I-Device
family	O
of	O
computers	O
.	O
</s>
<s>
A	O
TUTOR	B-Language
lesson	O
could	O
attach	O
a	O
single	O
region	O
of	O
up	O
to	O
1500	O
words	O
of	O
shared	O
memory	O
using	O
the	O
common	O
command	O
.	O
</s>
<s>
Each	O
lesson	O
could	O
have	O
an	O
unnamed	O
temporary	O
common	B-Application
block	I-Application
containing	O
variables	O
shared	O
by	O
all	O
users	O
of	O
that	O
lesson	O
.	O
</s>
<s>
In	O
contrast	O
,	O
named	O
common	B-Application
blocks	I-Application
were	O
associated	O
with	O
a	O
block	O
of	O
a	O
lesson	O
(	O
a	O
disk	O
file	O
)	O
.	O
</s>
<s>
For	O
example	O
(	O
from	O
page	O
X-11	O
of	O
The	O
TUTOR	B-Language
Language	O
,	O
Sherwood	O
,	O
1974	O
)	O
:	O
</s>
<s>
This	O
example	O
defines	O
nc1	O
to	O
nc1000	O
as	O
a	O
shared	O
unnamed	O
common	B-Application
block	I-Application
,	O
while	O
nc1001	O
to	O
nc1075	O
are	O
private	O
storage	O
.	O
</s>
<s>
The	O
Tutor	B-Language
define	O
command	O
was	O
very	O
similar	O
to	O
the	O
C	B-Language
#define	O
preprocessor	B-General_Concept
directive	O
.	O
</s>
<s>
(	O
underlining	O
from	O
the	O
original	O
,	O
page	O
IV-5	O
of	O
The	O
TUTOR	B-Language
Language	O
,	O
Sherwood	O
,	O
1974	O
.	O
)	O
</s>
<s>
Functions	O
could	O
be	O
defined	O
,	O
with	O
macro-substitution	O
semantics	O
,	O
as	O
in	O
this	O
illustration	O
from	O
page	O
IX-2	O
of	O
The	O
TUTOR	B-Language
Language	O
,	O
Sherwood	O
,	O
1974	O
:	O
</s>
<s>
Unlike	O
C	B-Language
,	O
the	O
original	O
scope	B-Language
rules	I-Language
of	O
TUTOR	B-Language
were	O
pure	O
"	O
definition	O
before	O
use	O
"	O
with	O
no	O
provisions	O
for	O
local	O
definitions	O
.	O
</s>
<s>
Later	O
in	O
the	O
development	O
of	O
TUTOR	B-Language
,	O
with	O
the	O
introduction	O
of	O
multiple	O
named	O
sets	O
of	O
definitions	O
,	O
the	O
programmer	O
was	O
given	O
explicit	O
control	O
over	O
which	O
sets	O
of	O
definitions	O
were	O
currently	O
in	O
force	O
.	O
</s>
<s>
The	O
original	O
TUTOR	B-Language
tools	O
for	O
text	O
manipulation	O
were	O
based	O
on	O
commands	O
for	O
specific	O
text	O
operations	O
,	O
for	O
example	O
,	O
pack	O
to	O
place	O
a	O
packed	O
character	O
string	O
into	O
consecutive	O
variables	O
in	O
memory	O
,	O
search	O
to	O
search	O
for	O
one	O
string	O
within	O
another	O
,	O
and	O
move	O
to	O
move	O
a	O
string	O
from	O
memory	O
to	O
memory	O
.	O
</s>
<s>
Page	O
14	O
of	O
PLATO	B-Operating_System
User	O
's	O
Memo	O
--	O
Summary	O
of	O
TUTOR	B-Language
Commands	O
and	O
System	O
Variables	O
,	O
Avner	O
,	O
1975	O
,	O
gives	O
the	O
following	O
:	O
</s>
<s>
Segmented	O
arrays	O
,	O
defined	O
with	O
the	O
keyword	O
segment	O
,	O
were	O
comparable	O
to	O
packed	O
arrays	O
in	O
Pascal	B-Application
.	O
</s>
<s>
Arbitrary	O
text	O
manipulation	O
could	O
be	O
done	O
by	O
setting	O
the	O
byte	O
size	O
to	O
the	O
machine	O
byte	O
size	O
,	O
6	O
bits	O
on	O
implementations	O
using	O
display	B-Application
code	I-Application
,	O
8	O
bits	O
on	O
some	O
later	O
ASCII	B-Protocol
and	O
extended	B-Protocol
ASCII	I-Protocol
implementations	O
.	O
</s>
<s>
A	O
general	O
parameter	O
passing	O
mechanism	O
was	O
added	O
to	O
TUTOR	B-Language
early	O
in	O
the	O
PLATO	B-Operating_System
IV	I-Operating_System
era	O
.	O
</s>
<s>
Page	O
IV-10	O
of	O
The	O
TUTOR	B-Language
Language	O
by	O
Sherwood	O
,	O
1974	O
gives	O
the	O
following	O
example	O
:	O
</s>
<s>
Local	O
variables	O
were	O
added	O
to	O
TUTOR	B-Language
some	O
time	O
around	O
1980	O
.	O
</s>
<s>
Having	O
done	O
so	O
,	O
a	O
unit	O
using	O
local	O
variables	O
could	O
begin	O
as	O
follows	O
(	O
from	O
Page	O
C2	O
of	O
Summary	O
of	O
TUTOR	B-Language
Commands	O
and	O
System	O
Variables	O
,	O
Avner	O
,	O
1981	O
)	O
:	O
</s>
<s>
The	O
continuation	O
lines	O
of	O
the	O
unit	O
command	O
given	O
above	O
are	O
taken	O
to	O
be	O
lines	O
of	O
an	O
implicit	O
define	O
command	O
with	O
local	O
scope	B-Language
.	O
</s>
<s>
The	O
available	O
TUTOR	B-Language
documentation	O
does	O
not	O
discuss	O
how	O
local	O
variables	O
are	O
allocated	O
.	O
</s>
<s>
There	O
has	O
been	O
a	O
sizable	O
family	O
of	O
TUTOR-related	O
languages	O
,	O
each	O
similar	O
to	O
the	O
original	O
TUTOR	B-Language
language	O
but	O
with	O
differences	O
.	O
</s>
<s>
In	O
particular	O
,	O
TUTOR	B-Language
was	O
a	O
component	O
of	O
a	O
system	O
(	O
the	O
PLATO	O
computer-based	O
education	O
system	O
)	O
that	O
ran	O
on	O
particular	O
CDC	O
mainframe	O
hardware	O
.	O
</s>
<s>
For	O
efficiency	O
,	O
there	O
were	O
some	O
hardware-specific	O
elements	O
in	O
TUTOR	B-Language
(	O
e.g.	O
</s>
<s>
Also	O
,	O
TUTOR	B-Language
was	O
designed	O
before	O
the	O
advent	O
of	O
the	O
windows-oriented	O
graphical	O
user	O
interface	O
(	O
GUI	O
)	O
.	O
</s>
<s>
The	O
microTutor	O
language	O
was	O
developed	O
in	O
the	O
PLATO	B-Operating_System
project	O
at	O
UIUC	O
to	O
permit	O
portions	O
of	O
a	O
lesson	O
to	O
run	O
in	O
terminals	O
that	O
contained	O
microcomputers	O
,	O
with	O
connections	O
to	O
TUTOR	B-Language
code	O
running	O
on	O
the	O
mainframe	O
.	O
</s>
<s>
The	O
Tencore	O
Language	O
Authoring	O
System	O
is	O
a	O
TUTOR	B-Language
derivative	O
developed	O
by	O
Paul	O
Tenczar	O
for	O
PCs	O
and	O
sold	O
by	O
Computer	O
Teaching	O
Corporation	O
.	O
</s>
<s>
cT	O
was	O
a	O
derivative	O
of	O
TUTOR	B-Language
and	O
microTutor	O
developed	O
at	O
Carnegie	O
Mellon	O
which	O
allowed	O
programs	O
to	O
run	O
without	O
change	O
in	O
windowed	O
GUI	O
environments	O
on	O
Windows	O
,	O
Mac	O
,	O
and	O
Unix/Linux	O
systems	O
.	O
</s>
