<s>
Darcs	B-Protocol
is	O
a	O
distributed	B-Protocol
version	I-Protocol
control	I-Protocol
system	I-Protocol
created	O
by	O
David	O
Roundy	O
.	O
</s>
<s>
Key	O
features	O
include	O
the	O
ability	O
to	O
choose	O
which	O
changes	O
to	O
accept	O
from	O
other	O
repositories	O
,	O
interaction	O
with	O
either	O
other	O
local	O
(	O
on-disk	O
)	O
repositories	O
or	O
remote	O
repositories	O
via	O
SSH	B-Protocol
,	O
HTTP	B-Protocol
,	O
or	O
email	O
,	O
and	O
an	O
unusually	O
interactive	O
interface	O
.	O
</s>
<s>
The	O
developers	O
also	O
emphasize	O
the	O
use	O
of	O
advanced	O
software	O
tools	O
for	O
verifying	O
correctness	O
:	O
the	O
expressive	O
type	O
system	O
of	O
the	O
functional	B-Language
programming	I-Language
language	I-Language
Haskell	B-Language
enforces	O
some	O
properties	O
,	O
and	O
randomized	O
testing	O
via	O
QuickCheck	B-Application
verifies	O
many	O
others	O
.	O
</s>
<s>
The	O
name	O
is	O
a	O
recursive	O
acronym	O
for	O
Darcs	B-Protocol
Advanced	O
Revision	B-Architecture
Control	I-Architecture
System	I-Architecture
.	O
</s>
<s>
Darcs	B-Protocol
treats	O
patches	O
as	O
first-class	O
citizens	O
.	O
</s>
<s>
Many	O
branching	O
,	O
merging	B-General_Concept
,	O
and	O
cherry-picking	O
operations	O
that	O
would	O
require	O
additional	O
commands	O
with	O
snapshot-based	O
systems	O
like	O
Git	B-Application
or	O
Mercurial	B-Protocol
can	O
be	O
directly	O
done	O
with	O
Darcs	B-Protocol
with	O
the	O
usual	O
"	O
pull	O
"	O
and	O
"	O
push	O
"	O
commands	O
.	O
</s>
<s>
In	O
terms	O
of	O
user	O
interface	O
,	O
this	O
means	O
that	O
Darcs	B-Protocol
has	O
fewer	O
commands	O
.	O
</s>
<s>
Darcs	B-Protocol
automatically	O
calculates	O
whether	O
patches	O
can	O
be	O
reordered	O
(	O
an	O
operation	O
called	O
commutation	O
)	O
,	O
and	O
how	O
to	O
do	O
it	O
.	O
</s>
<s>
A	O
Darcs	B-Protocol
patch	O
can	O
contain	O
changes	O
of	O
the	O
following	O
kinds	O
:	O
</s>
<s>
To	O
address	O
cases	O
when	O
this	O
is	O
not	O
desirable	O
,	O
Darcs	B-Protocol
enables	O
the	O
user	O
to	O
specify	O
explicit	O
dependencies	O
between	O
patches	O
.	O
</s>
<s>
Since	O
version	O
2.10	O
,	O
Darcs	B-Protocol
uses	O
patience	O
diff	O
by	O
default	O
.	O
</s>
<s>
Darcs	B-Protocol
evolved	O
out	O
of	O
David	O
Roundy	O
's	O
efforts	O
to	O
design	O
a	O
new	O
patch	O
format	O
for	O
GNU	B-Protocol
arch	I-Protocol
in	O
June	O
2002	O
.	O
</s>
<s>
After	O
writing	O
an	O
initial	O
version	O
of	O
Darcs	B-Protocol
in	O
C++	B-Language
,	O
the	O
Haskell	B-Language
version	O
was	O
written	O
in	O
Autumn	O
2002	O
and	O
released	O
to	O
the	O
public	O
in	O
April	O
2003	O
.	O
</s>
<s>
Darcs	B-Protocol
2.0	O
was	O
released	O
in	O
April	O
2008	O
and	O
introduced	O
a	O
more	O
robust	O
repository	O
format	O
,	O
as	O
well	O
as	O
a	O
new	O
patch	O
semantic	O
called	O
"	O
darcs-2	O
"	O
,	O
aimed	O
at	O
minimizing	O
exponential	O
merge	B-Operating_System
conflicts	I-Operating_System
.	O
</s>
<s>
Darcs	B-Protocol
has	O
been	O
criticized	O
on	O
the	O
grounds	O
of	O
performance	O
.	O
</s>
<s>
One	O
of	O
the	O
most	O
notable	O
challenges	O
related	O
to	O
the	O
merge	B-General_Concept
algorithm	O
in	O
Darcs	B-Protocol
1.x	O
,	O
which	O
could	O
do	O
exponential	O
work	O
to	O
merge	B-General_Concept
some	O
conflicts	O
.	O
</s>
<s>
Although	O
it	O
was	O
not	O
completely	O
corrected	O
in	O
Darcs	B-Protocol
2	O
,	O
the	O
frequency	O
of	O
exponential	O
merges	B-General_Concept
has	O
been	O
reduced	O
.	O
</s>
<s>
Bugs	O
still	O
remain	O
in	O
which	O
merging	B-General_Concept
of	O
recursive	O
conflicts	O
fails	O
.	O
</s>
<s>
The	O
revision	B-Architecture
control	I-Architecture
system	I-Architecture
Pijul	O
solves	O
those	O
complexity	O
problems	O
by	O
making	O
conflicts	O
and	O
their	O
resolutions	O
first	O
class	O
citizens	O
which	O
can	O
commute	O
with	O
other	O
changes	O
.	O
</s>
