<s>
UCBLogo	B-Application
,	O
also	O
termed	O
Berkeley	O
Logo	B-Device
,	O
is	O
a	O
programming	O
language	O
,	O
a	O
dialect	O
of	O
Logo	B-Device
,	O
which	O
derived	O
from	O
Lisp	B-Language
.	O
</s>
<s>
It	O
is	O
a	O
dialect	O
of	O
Logo	B-Device
intended	O
to	O
being	O
a	O
“	O
minimum	O
Logo	B-Device
standard.	O
”	O
It	O
has	O
the	O
best	O
facilities	O
for	O
handling	O
lists	O
,	O
files	B-Operating_System
,	O
input/output	B-General_Concept
(	O
I/O	B-General_Concept
)	O
,	O
and	O
recursion	O
.	O
</s>
<s>
It	O
can	O
be	O
used	O
to	O
teach	O
most	O
computer	O
science	O
concepts	O
,	O
as	O
University	O
of	O
California	O
,	O
Berkeley	O
lecturer	O
Brian	O
Harvey	O
did	O
in	O
his	O
Computer	O
Science	O
Logo	B-Device
Style	O
trilogy	O
.	O
</s>
<s>
It	O
is	O
free	B-License
and	I-License
open-source	I-License
software	I-License
released	O
under	O
a	O
GNU	B-License
General	I-License
Public	I-License
License	I-License
(	O
GPL	B-License
)	O
.	O
</s>
<s>
UCBLogo	B-Application
has	O
a	O
rudimentary	O
graphical	B-Application
user	I-Application
interface	I-Application
(	O
GUI	B-Application
)	O
,	O
so	O
several	O
projects	O
exist	O
that	O
provide	O
a	O
better	O
interface	O
.	O
</s>
<s>
MSWLogo	B-Application
and	O
its	O
successor	O
FMSLogo	B-Application
,	O
for	O
Microsoft	B-Application
Windows	I-Application
,	O
are	O
commonly	O
used	O
in	O
schools	O
in	O
the	O
United	O
Kingdom	O
and	O
Australia	O
.	O
</s>
<s>
Logo	B-Device
was	O
designed	O
in	O
spirit	O
of	O
low	O
threshold	O
and	O
no	O
ceiling	O
,	O
which	O
enables	O
easy	O
entry	O
by	O
novices	O
and	O
yet	O
meet	O
the	O
needs	O
of	O
high-powered	O
users	O
.	O
</s>
<s>
The	O
turtle	O
can	O
be	O
set	O
to	O
erase	O
anything	O
below	O
it	O
,	O
using	O
the	O
command	O
PENERASE	O
(	O
PE	O
)	O
,	O
while	O
the	O
pen	O
can	O
be	O
set	O
to	O
start	O
drawing	O
again	O
with	O
the	O
command	O
PENPAINT	O
(	O
PPT	O
)	O
,	O
in	O
UCBLogo	B-Application
.	O
</s>
<s>
There	O
are	O
three	O
datatypes	O
in	O
UCBLogo	B-Application
:	O
</s>
<s>
x	O
:=	O
y	O
+	O
3	O
)	O
is	O
handled	O
in	O
Logo	B-Device
with	O
the	O
make	O
command	O
,	O
as	O
exemplified	O
by	O
these	O
two	O
equivalent	O
statements	O
:	O
</s>
<s>
Variables	O
do	O
not	O
have	O
to	O
be	O
declared	O
before	O
use	O
;	O
their	O
scope	B-Language
is	O
then	O
global	O
.	O
</s>
<s>
A	O
variable	O
may	O
be	O
declared	O
local	O
,	O
then	O
its	O
scope	B-Language
is	O
limited	O
to	O
that	O
procedure	O
and	O
any	O
procedures	O
that	O
it	O
calls	O
,	O
which	O
is	O
termed	O
dynamic	B-Language
scope	B-Language
.	O
</s>
<s>
Calling	O
a	O
procedure	O
with	O
inputs	O
(	O
the	O
name	O
usually	O
used	O
for	O
arguments	O
in	O
the	O
Logo	B-Device
literature	O
)	O
also	O
creates	O
local	O
variables	O
that	O
hold	O
the	O
argument	O
values	O
.	O
</s>
<s>
Logo	B-Device
inherits	O
lists	O
from	O
Lisp	B-Language
,	O
and	O
they	O
are	O
its	O
main	O
method	O
to	O
store	O
vectors	O
.	O
</s>
<s>
Logo	B-Device
provides	O
several	O
common	O
control	O
structures	O
.	O
</s>
<s>
There	O
is	O
one	O
conditional	B-Language
structure	I-Language
.	O
</s>
<s>
Recursion	O
is	O
Logo	B-Device
's	O
preferred	O
processing	O
paradigm	O
.	O
</s>
<s>
Logo	B-Device
also	O
provides	O
list-based	O
control	O
structures	O
.	O
</s>
<s>
The	O
Hello	O
World	O
program	O
in	O
Logo	B-Device
looks	O
like	O
this	O
:	O
</s>
<s>
A	O
command	O
is	O
similar	O
to	O
a	O
Pascal	B-Application
procedure	O
,	O
and	O
an	O
operation	O
is	O
similar	O
to	O
a	O
Pascal	B-Application
function	O
.	O
</s>
<s>
(	O
See	O
also	O
:	O
command-query	B-Application
separation	I-Application
,	O
where	O
a	O
query	O
is	O
an	O
operation	O
in	O
Logo	B-Device
)	O
.	O
</s>
<s>
A	O
special	O
subset	O
of	O
operations	O
,	O
called	O
predicates	B-Algorithm
,	O
which	O
just	O
output	O
the	O
word	O
true	O
or	O
false	O
,	O
are	O
conventionally	O
written	O
with	O
a	O
final	O
p	O
.	O
Examples	O
include	O
emptyp	O
,	O
wordp	O
,	O
and	O
listp	O
.	O
</s>
<s>
However	O
,	O
in	O
some	O
early	O
Logos	B-Device
the	O
procedure	O
is	O
limited	O
to	O
the	O
physical	O
line	O
length	O
of	O
the	O
input	O
device	O
.	O
</s>
<s>
All	O
Logos	B-Device
can	O
invoke	O
an	O
Editor	O
,	O
usually	O
by	O
EDALL	O
.	O
</s>
<s>
The	O
new	O
word	O
is	O
saved	O
into	O
the	O
available	O
vocabulary	O
,	O
but	O
the	O
definition	O
will	O
be	O
lost	O
once	O
the	O
Logo	B-Device
session	O
is	O
over	O
.	O
</s>
<s>
Logo	B-Device
can	O
pass	O
extra	O
information	O
to	O
its	O
words	O
,	O
and	O
return	O
information	O
.	O
</s>
<s>
Mathematics	O
in	O
Logo	B-Device
uses	O
prefix	O
or	O
Polish	O
notation	O
,	O
like	O
:	O
.	O
</s>
<s>
Logo	B-Device
allows	O
for	O
recursion	O
,	O
a	O
process	O
where	O
a	O
procedure	O
calls	O
itself	O
.	O
</s>
