8.12
Double Linked Ring
| (require data/double-linked-ring) | |
| package: double-linked-ring | |
A double linked ring data structure. A ring has no beginning or end, it only has a current element.
Determines if buff is a ring buffer.
Create a ring from a list. If the list isn’t specified
an empty ring is created. The current element of the ring
is set to the first element of the list.
procedure
(ring->list a-ring) → list?
a-ring : ring?
Creates a list of the element in the ring starting from
the current one.
Examples:
> (define the-ring (ring '(a b c d))) > (ring->list the-ring) '(a b c d)
procedure
(ring-size a-ring) → exact-nonnegative-integer?
a-ring : ring?
Returns the number of elements of the ring.
procedure
(ring-current a-ring) → any/c
a-ring : ring?
Returns the current element of the ring. If the ring is
empty an exception is raised.
Examples:
> (define the-ring (ring)) > (ring-size the-ring) 0
> (ring-current the-ring) ring-current: the ring is empty
> (define the-ring (ring '(a b c d))) > (ring-size the-ring) 4
> (ring-current the-ring) 'a
procedure
(ring-next! a-ring) → any/c
a-ring : ring?
Returns the next element of the ring and sets the current
element to this element. If the ring is empty an exception
is raised.
procedure
(ring-prev! a-ring) → any/c
a-ring : ring?
Returns the previous element of the ring and sets the current
element to this element. If the ring is empty an exception
is raised.
Examples:
> (define the-ring (ring '(a b c d))) > (ring-current the-ring) 'a
> (ring-next! the-ring) 'b
> (ring-current the-ring) 'b
> (ring->list the-ring) '(b c d a)
> (ring-prev! the-ring) 'a
> (ring-prev! the-ring) 'd
> (ring-current the-ring) 'd
> (ring->list the-ring) '(d a b c)
procedure
(ring-remove-current! a-ring) → void?
a-ring : ring?
Removes the current element of the ring and sets the current
element to the next element. If the ring is empty an exception
is raised.
procedure
(ring-set-current! a-ring elem) → void?
a-ring : ring? elem : any/c
Sets the current element to elem with set!.
If the ring is empty an exception is raised.
Examples:
> (define the-ring (ring '(a b c d))) > (ring-set-current! the-ring 'A) > (ring->list the-ring) '(A b c d)
> (ring-remove-current! the-ring) > (ring->list the-ring) '(b c d)
procedure
(ring-add-next! a-ring elem) → void?
a-ring : ring? elem : any/c
Adds a new elem after the current one and sets the new
elem as current.
procedure
(ring-add-prev! a-ring elem) → void?
a-ring : ring? elem : any/c
Adds a new elem before the current one and sets the new
elem as current.
Examples:
> (define the-ring (ring '(a b c d))) > (ring-add-prev! the-ring 1) > (ring-add-prev! the-ring 2) > (ring-add-prev! the-ring 3) > (ring->list the-ring) '(3 2 1 a b c d)
> (set! the-ring (ring '(a b c d))) > (ring-add-next! the-ring 1) > (ring-add-next! the-ring 2) > (ring-add-next! the-ring 3) > (ring->list the-ring) '(3 b c d a 1 2)
The procedure ring->list can be quite confusing. I use it mainly for debugging purposes.