<s>
In	O
computational	O
combinatorics	O
,	O
a	O
loopless	B-Algorithm
algorithm	I-Algorithm
or	O
loopless	B-Algorithm
imperative	I-Algorithm
algorithm	I-Algorithm
is	O
an	O
imperative	B-Application
algorithm	O
that	O
generates	O
successive	O
combinatorial	O
objects	O
,	O
such	O
as	O
partitions	O
,	O
permutations	B-Algorithm
,	O
and	O
combinations	O
,	O
in	O
constant	O
time	O
and	O
the	O
first	O
object	O
in	O
linear	O
time	O
.	O
</s>
<s>
A	O
loopless	B-Algorithm
functional	I-Algorithm
algorithm	I-Algorithm
is	O
a	O
functional	B-Language
algorithm	O
that	O
takes	O
the	O
form	O
unfoldr	O
step	O
•	O
prolog	O
where	O
step	O
takes	O
constant	O
time	O
and	O
prolog	O
takes	O
linear	O
time	O
in	O
the	O
size	O
of	O
the	O
input	O
.	O
</s>
<s>
The	O
standard	O
function	O
unfoldr	O
is	O
a	O
right-associative	O
Bird	O
unfold	B-Application
.	O
</s>
