<s>
Alef	B-Application
is	O
a	O
discontinued	O
concurrent	B-Architecture
programming	I-Architecture
language	O
,	O
designed	O
as	O
part	O
of	O
the	O
Plan	B-Operating_System
9	I-Operating_System
operating	B-General_Concept
system	I-General_Concept
by	O
Phil	O
Winterbottom	O
of	O
Bell	O
Labs	O
.	O
</s>
<s>
It	O
implemented	O
the	O
channel-based	O
concurrency	B-Operating_System
model	O
of	O
Newsqueak	B-Language
in	O
a	O
compiled	B-Language
,	O
C-like	O
language	O
.	O
</s>
<s>
Alef	B-Application
appeared	O
in	O
the	O
first	O
and	O
second	O
editions	O
of	O
Plan	B-Operating_System
9	I-Operating_System
,	O
but	O
was	O
abandoned	O
during	O
development	O
of	O
the	O
third	O
edition	O
.	O
</s>
<s>
Rob	O
Pike	O
later	O
explained	O
Alef	B-Application
's	O
demise	O
by	O
pointing	O
to	O
its	O
lack	O
of	O
automatic	B-General_Concept
memory	I-General_Concept
management	I-General_Concept
,	O
despite	O
Pike	O
's	O
and	O
other	O
people	O
's	O
urging	O
Winterbottom	O
to	O
add	O
garbage	B-General_Concept
collection	I-General_Concept
to	O
the	O
language	O
;	O
</s>
<s>
also	O
,	O
in	O
a	O
February	O
2000	O
slideshow	O
,	O
Pike	O
noted	O
:	O
"	O
…	O
although	O
Alef	B-Application
was	O
a	O
fruitful	O
language	O
,	O
it	O
proved	O
too	O
difficult	O
to	O
maintain	O
a	O
variant	O
language	O
across	O
multiple	O
architectures	O
,	O
so	O
we	O
took	O
what	O
we	O
learned	O
from	O
it	O
and	O
built	O
the	O
thread	O
library	B-Library
for	O
C.	O
"	O
</s>
<s>
Alef	B-Application
was	O
superseded	O
by	O
two	O
programming	O
environments	O
.	O
</s>
<s>
The	O
Limbo	B-Application
programming	I-Application
language	I-Application
can	O
be	O
considered	O
a	O
direct	O
successor	O
of	O
Alef	B-Application
and	O
is	O
the	O
most	O
commonly	O
used	O
language	O
in	O
the	O
Inferno	B-Operating_System
operating	I-Operating_System
system	I-Operating_System
.	O
</s>
<s>
The	O
Alef	B-Application
concurrency	B-Operating_System
model	O
was	O
replicated	O
in	O
the	O
third	O
edition	O
of	O
Plan	B-Operating_System
9	I-Operating_System
in	O
the	O
form	O
of	O
the	O
libthread	O
library	B-Library
,	O
which	O
makes	O
some	O
of	O
Alef	B-Application
's	O
functionality	O
available	O
to	O
C	B-Language
programs	I-Language
and	O
allowed	O
existing	O
Alef	B-Application
programs	O
(	O
such	O
as	O
Acme	B-Application
)	O
to	O
be	O
translated	O
.	O
</s>
<s>
This	O
example	O
was	O
taken	O
from	O
the	O
Alef	B-Application
reference	O
manual	O
.	O
</s>
<s>
The	O
piece	O
illustrates	O
the	O
use	O
of	O
tuple	B-Application
data	O
type	O
.	O
</s>
