A double ended queue that can shrink and expand on both ends.
An index is assigned to an element when it enters the queue, and the index of an element is static (i.e. an index refers to a distinct element until that element is removed from the queue, no matter how many intervening push/pop operations occur).
One consequence of this is that the minimum index may be < 0.
The "front" is the smallest valid index, while the "back" is the largest.
All operations are amortized O(1) with a small constant.
create ?initial_length ?never_shrink ()
create a new t
. initial_length
is the
initial length of the dequeue; it will be able to hold initial_length
elements
without resizing. It must be positive. If never_shrink
is true, the physical array
will never shrink; only expand. If initial_length
is given without never_shrink
then never_shrink
is presumed to be true
, otherwise never_shrink
defaults to
false
.
front_index_exn t
throws an exception if t
is empty, otherwise returns the index
of the front item in t
back_index_exn t
throws an exception if t
is empty, otherwise returns the index
of the back item in t
get_opt t i
return the element at index i
. Return None
if i
is invalid.
get t i
return the element at index i
. Raise an exception if i
is
invalid.
peek t back_or_front
return the value at the back or front of the dequeue without
removing it.
iter' t ~f
iter over the elements of t
.
iteri t ~f
iter over the elements of t `front_to_back
passing in the index.
iteri' t ~f
as iter
, but also passes in the index of the current element.
fold' t ~init ~f
fold over the elements of t
foldi t ~init ~f
as fold
, but also passes in the index of the current element.
foldi' t ~init ~f
as fold'
, but also passes in the index of the current element to
f
.
enqueue t back_or_front v
push v
onto the back_or_front
of t
.
drop ?n t back_or_front
drop n
elements (default 1) from the back_or_front
of
t
. If t
has fewer than n
elements then it is cleared.