<s>
GNU	B-Operating_System
Dr.	B-Application
Geo	I-Application
is	O
interactive	B-Application
geometry	I-Application
software	I-Application
that	O
allows	O
its	O
users	O
to	O
design	O
&	O
manipulate	O
interactive	O
geometric	O
sketches	O
.	O
</s>
<s>
It	O
is	O
free	O
software	O
(	O
source	O
code	O
,	O
translations	O
,	O
icons	O
and	O
installer	O
are	O
released	O
under	O
GNU	B-License
GPL	I-License
license	I-License
)	O
,	O
created	O
by	O
Hilaire	O
Fernandes	O
,	O
it	O
is	O
part	O
of	O
the	O
GNU	B-Operating_System
project	O
.	O
</s>
<s>
It	O
runs	O
over	O
a	O
Morphic	O
graphic	O
system	O
(	O
which	O
means	O
that	O
it	O
runs	O
on	O
Linux	B-Application
,	O
Mac	O
OS	O
,	O
Windows	B-Application
,	O
Android	O
)	O
.	O
</s>
<s>
Current	O
version	O
of	O
Dr.	B-Application
Geo	I-Application
is	O
also	O
called	O
Dr.	B-Application
Geo	I-Application
II	O
.	O
</s>
<s>
Historically	O
Dr.	B-Application
Geo	I-Application
was	O
developed	O
in	O
C++	O
and	O
Dr.	B-Application
Geo	I-Application
II	O
is	O
a	O
complete	O
rewrite	O
using	O
Pharo	B-Language
that	O
happened	O
in	O
2005	O
.	O
</s>
<s>
Dr.	B-Application
Geo	I-Application
manipulates	O
different	O
kinds	O
of	O
objects	O
such	O
as	O
points	O
,	O
lines	O
,	O
circles	O
,	O
block	O
of	O
code	O
.	O
</s>
<s>
Dr.	B-Application
Geo	I-Application
has	O
several	O
kinds	O
of	O
points	O
:	O
a	O
free	O
point	O
,	O
which	O
can	O
be	O
moved	O
with	O
the	O
mouse	O
(	O
but	O
may	O
be	O
attached	O
to	O
a	O
curve	O
)	O
and	O
a	O
point	O
given	O
by	O
its	O
coordinates	O
.	O
</s>
<s>
Points	O
can	O
also	O
be	O
created	O
as	O
the	O
intersection	B-Algorithm
of	O
2	O
curves	O
or	O
as	O
the	O
midpoint	O
of	O
a	O
segment	O
.	O
</s>
<s>
Dr.	B-Application
Geo	I-Application
is	O
equipped	O
with	O
the	O
classic	O
line	O
,	O
ray	O
,	O
segment	O
and	O
vector	O
.	O
</s>
<s>
Besides	O
the	O
parallel	O
and	O
perpendicular	O
line	O
through	O
a	O
point	O
,	O
Dr.	B-Application
Geo	I-Application
can	O
apply	O
to	O
a	O
point	O
or	O
a	O
line	O
one	O
of	O
these	O
transformations	O
:	O
</s>
<s>
Dr.	B-Application
Geo	I-Application
comes	O
with	O
macro-construction	O
:	O
a	O
way	O
to	O
teach	O
Dr.	B-Application
Geo	I-Application
new	O
constructions	O
.	O
</s>
<s>
It	O
allows	O
to	O
add	O
new	O
objects	O
to	O
Dr.	B-Application
Geo	I-Application
:	O
new	O
transformations	O
like	O
circle	O
inversion	O
,	O
tedious	O
constructions	O
involving	O
a	O
lot	O
of	O
intermediate	O
objects	O
or	O
constructions	O
involving	O
script	O
(	O
also	O
named	O
macro-script	O
)	O
.	O
</s>
<s>
Access	O
to	O
user	O
programming	O
is	O
at	O
the	O
essence	O
of	O
Dr.	B-Application
Geo	I-Application
:	O
from	O
the	O
software	O
,	O
the	O
user	O
can	O
directly	O
read	O
,	O
study	O
,	O
modify	O
and	O
redistribute	O
modified	O
version	O
of	O
Dr.	B-Application
Geo	I-Application
.	O
</s>
<s>
Dr.	B-Application
Geo	I-Application
source	O
code	O
is	O
Pharo	B-Language
.	O
</s>
<s>
It	O
is	O
also	O
the	O
language	O
used	O
for	O
user	O
programming	O
:	O
to	O
extend	O
Dr.	B-Application
Geo	I-Application
with	O
arbitrary	O
computing	O
operations	O
(	O
Pharo	B-Language
script	O
)	O
and	O
to	O
define	O
a	O
geometric	O
sketch	O
entirely	O
with	O
programming	O
instructions	O
(	O
Pharo	B-Language
sketch	O
)	O
.	O
</s>
<s>
Dr.	B-Application
Geo	I-Application
is	O
shipped	O
with	O
its	O
source	O
code	O
and	O
the	O
developer	O
tools	O
.	O
</s>
<s>
Therefore	O
its	O
code	O
can	O
be	O
edited	O
and	O
recompiled	O
from	O
Dr.	B-Application
Geo	I-Application
while	O
it	O
is	O
functioning	O
.	O
</s>
<s>
This	O
design	O
,	O
inherited	O
from	O
Pharo	B-Language
,	O
makes	O
easy	O
to	O
test	O
new	O
ideas	O
and	O
new	O
designs	O
.	O
</s>
<s>
A	O
script	O
is	O
a	O
first	O
class	O
object	O
defined	O
along	O
Dr.	B-Application
Geo	I-Application
code	O
.	O
</s>
<s>
Dr.	B-Application
Geo	I-Application
Pharo	B-Language
sketches	O
are	O
sketches	O
entirely	O
defined	O
in	O
the	O
Pharo	B-Language
language	O
.	O
</s>
<s>
This	O
is	O
not	O
about	O
constructing	O
a	O
sketch	O
with	O
the	O
Dr.	B-Application
Geo	I-Application
graphical	O
interface	O
,	O
but	O
about	O
describing	O
a	O
sketch	O
with	O
the	O
Pharo	B-Language
language	O
.	O
</s>
<s>
A	O
Fibonacci	O
spiral	O
programmed	O
with	O
geometric	O
transformations	O
(	O
rotation	O
,	O
translation	O
and	O
homothety	B-Algorithm
)	O
:	O
</s>
<s>
Pharo	B-Language
sktech	O
can	O
be	O
used	O
to	O
design	O
interactive	O
sketch	O
demonstrating	O
numerical	O
analysis	O
method	O
:	O
</s>
<s>
A	O
French	O
version	O
of	O
the	O
Pharo	B-Language
sketch	O
API	O
makes	O
possible	O
writing	O
source	O
code	O
in	O
this	O
language	O
:	O
</s>
