2 Deques

8.14.0.1

2 Deques🔗ℹ

Double ended queues (or deque) are queues where elements can be added or removed from either end. The deque data structures provided by this library implement and provide the following operations: deque, empty?, enqueue, enqueue-front, head, tail, last, init and deque->list.

2.1 Bankers Deque

2.2 Implicit Deque

2.3 Real-Time Deque

2.1 Bankers Deque🔗ℹ

(require pfds/deque/bankers)

package: pfds

Bankers deques are amortized double ended deques developed using the Bankers method. They provide an amortized running time of O(1) for the operations head, tail, last, init, enqueue-front and enqueue. They use lazy evaluation and memoization to achieve the amortized running time.

syntax
(Deque A)

A banker’s deque of type A.

procedure
(deque a ...) → (Deque A)
a : A

Function deque creates a Bankers Deque with the given inputs.

Example:

> (deque 1 2 3 4 5 6)
- : #(struct:Deque
      ((Rec
        g298138
        (U (Pairof Positive-Byte g298138) (Promiseof g298138) Null))
       Integer
       (Rec
        g298140
        (U (Pairof Positive-Byte g298140) (Promiseof g298140) Null))
       Integer))
#<Deque>

In the above example, the deque obtained will have 1 as its head element.

procedure
(empty t) → (Deque A)
t : A

An empty deque of type t.

Examples:

> (empty Nothing)
- : (Deque Nothing)
#<Deque>
> (empty Integer)
- : (Deque Integer)
#<Deque>

procedure
(empty? dq) → Boolean
dq : (Deque A)

Function empty? checks if the given deque is empty.

Examples:

> (empty? (empty Natural))
- : Boolean
#t
> (empty? (deque 1 2))
- : Boolean
#f

procedure
(enqueue a deq) → (Deque A)
a : A
deq : (Deque A)

Function enqueue takes an element and a deque and enqueues the given element in the deque.

Example:

> (enqueue 10 (deque 3 2 4))
- : #(struct:Deque
      ((Rec
        g298210
        (U (Pairof Positive-Byte g298210) (Promiseof g298210) Null))
       Integer
       (Rec
        g298212
        (U (Pairof Positive-Byte g298212) (Promiseof g298212) Null))
       Integer))
#<Deque>

In the above example, (enqueue 10 deq) adds the element 10 to (deque 3 2 4). 10 will be the last element in the deque.

procedure
(enqueue-front a deq) → (Deque A)
a : A
deq : (Deque A)

Function enqueue-front takes an element and a deque and puts the given element to the front of the given deque.

Example:

> (enqueue-front 10 (deque 5 6 3 4))
- : #(struct:Deque
      ((Rec
        g298231
        (U (Pairof Positive-Byte g298231) (Promiseof g298231) Null))
       Integer
       (Rec
        g298233
        (U (Pairof Positive-Byte g298233) (Promiseof g298233) Null))
       Integer))
#<Deque>

In the above example, (enqueue-front 10 (deque 5 6 3 4)) adds 10 to the front of the (deque 5 6 3 4). 10 will be the head element.

procedure
(head deq) → A
deq : (Deque A)

Function head takes a deque and gives the first element in the deque if deque is not empty else throws an error.

Examples:

> (head (deque 5 2 3))
- : Integer [more precisely: Positive-Byte]
5
> (head (empty Integer))
head: given deque is empty

In the above example, (head (empty Integer)) throws an error since the given deque is empty.

procedure
(last deq) → A
deq : (Deque A)

Function last takes a deque and gives the last element in the deque if deque is not empty else throws an error.

Examples:

> (last (deque 1 2 3 4 5 6))
- : Integer [more precisely: Positive-Byte]
6
> (last (empty Integer))
last: given deque is empty

In the above example, (last (empty Integer))throws an error since the given deque is empty.

procedure
(tail deq) → (Deque A)
deq : (Deque A)

Function tail takes a deque and returns the given deque without the first element if the given deque is non empty else throws an error.

Examples:

> (tail (deque 1 2 3 4 5 6))
- : #(struct:Deque
      ((Rec
        g298325
        (U (Pairof Positive-Byte g298325) (Promiseof g298325) Null))
       Integer
       (Rec
        g298327
        (U (Pairof Positive-Byte g298327) (Promiseof g298327) Null))
       Integer))
#<Deque>
> (tail (empty Integer))
tail: given deque is empty

In the above example, (tail (deque 1 2 3 4 5 6)), removes the head of the given deque returns (deque 2 3 4 5 6).

procedure
(init deq) → (Deque A)
deq : (Deque A)

Function init takes a deque and returns the given deque without the last element if the given deque is not empty else throws an error.

Examples:

> (init (deque 1 2 3 4 5 6))
- : #(struct:Deque
      ((Rec
        g298368
        (U (Pairof Positive-Byte g298368) (Promiseof g298368) Null))
       Integer
       (Rec
        g298370
        (U (Pairof Positive-Byte g298370) (Promiseof g298370) Null))
       Integer))
#<Deque>
> (init (empty Integer))
init: given deque is empty

In the above example, (init (deque 1 2 3 4 5 6)), removes the last element 6 and returns (deque 1 2 3 4 5).

procedure
(deque->list deq) → (Listof A)
deq : (Deque A)

Function deque->list takes a deque and returns a list of elements. The list will have head of the given deque as its first element. If the given deque is empty, then it returns an empty list.

Examples:

> (deque->list (deque 10 2 34 4 15 6))
- : (Listof Positive-Byte)
'(10 2 34 4 15 6)
> (deque->list (empty Integer))
- : (Listof Integer)
'()

procedure
(map func deq1 deq2 ...) → (Deque A)
  func : (A B ... B -> C)
  deq1 : (Deque A)
  deq2 : (Deque B)

Function map is similar to map for lists.

Examples:

> (deque->list (map add1 (deque 1 2 3 4 5 6)))
- : (Listof Positive-Index)
'(2 3 4 5 6 7)
> (deque->list (map * (deque 1 2 3 4 5 6) (deque 1 2 3 4 5 6)))
- : (Listof Positive-Index)
'(1 4 9 16 25 36)

procedure
(foldl func init deq1 deq2 ...) → C
  func : (C A B ... B -> C)
  init : C
  deq1 : (Deque A)
  deq2 : (Deque B)

Function foldl is similar to foldl

foldl currently does not produce correct results when the given function is non-commutative.

Examples:

> (foldl + 0 (deque 1 2 3 4 5 6))
- : Integer [more precisely: Nonnegative-Integer]
21
> (foldl * 1 (deque 1 2 3 4 5 6) (deque 1 2 3 4 5 6))
- : Integer [more precisely: Positive-Integer]
518400

procedure
(foldr func init deq1 deq2 ...) → C
  func : (C A B ... B -> C)
  init : C
  deq1 : (Deque A)
  deq2 : (Deque B)

Function foldr is similar to foldr

foldr currently does not produce correct results when the given function is non-commutative.

Examples:

> (foldr + 0 (deque 1 2 3 4 5 6))
- : Integer [more precisely: Nonnegative-Integer]
21
> (foldr * 1 (deque 1 2 3 4 5 6) (deque 1 2 3 4 5 6))
- : Integer [more precisely: Positive-Integer]
518400

procedure
(filter func que) → (Deque A)
func : (A -> Boolean)
que : (Deque A)

Function filter is similar to filter.

Examples:

> (define que (deque 1 2 3 4 5 6))
> (deque->list (filter (λ: ([x : Integer]) (> x 5)) que))
- : (Listof Positive-Byte)
'(6)
> (deque->list (filter (λ: ([x : Integer]) (< x 5)) que))
- : (Listof Positive-Byte)
'(1 2 3 4)
> (deque->list (filter (λ: ([x : Integer]) (<= x 5)) que))
- : (Listof Positive-Byte)
'(1 2 3 4 5)

procedure
(remove func que) → (Deque A)
func : (A -> Boolean)
que : (Deque A)

Function remove is similar to filter but remove removes the elements which match the predicate.

Examples:

> (deque->list (remove (λ: ([x : Integer]) (> x 5))
                       (deque 1 2 3 4 5 6)))
- : (Listof Positive-Byte)
'(1 2 3 4 5)
> (deque->list (remove (λ: ([x : Integer]) (< x 5))
                       (deque 1 2 3 4 5 6)))
- : (Listof Positive-Byte)
'(5 6)
> (deque->list (remove (λ: ([x : Integer]) (<= x 5))
                       (deque 1 2 3 4 5 6)))
- : (Listof Positive-Byte)
'(6)

procedure
(andmap func deq1 deq2 ...) → Boolean
  func : (A B ... B -> Boolean)
  deq1 : (Deque A)
  deq2 : (Deque B)

Function andmap is similar to andmap.

Examples:

> (andmap even? (deque 1 2 3 4 5 6))
- : Boolean
#f
> (andmap odd? (deque 1 2 3 4 5 6))
- : Boolean
#f
> (andmap positive? (deque 1 2 3 4 5 6))
- : Boolean
#t
> (andmap negative? (deque -1 -2))
- : Boolean
#t

procedure
(ormap func deq1 deq2 ...) → Boolean
  func : (A B ... B -> Boolean)
  deq1 : (Deque A)
  deq2 : (Deque B)

Function ormap is similar to ormap.

Examples:

> (ormap even? (deque 1 2 3 4 5 6))
- : Boolean
#t
> (ormap odd? (deque 1 2 3 4 5 6))
- : Boolean
#t
> (ormap positive? (deque -1 -2 3 4 -5 6))
- : Boolean
#t
> (ormap negative? (deque 1 -2))
- : Boolean
#t

procedure
(build-deque size func) → (Deque A)
size : Natural
func : (Natural -> A)

Function build-deque is similar to build-list.

Examples:

> (deque->list (build-deque 5 (λ:([x : Integer]) (add1 x))))
- : (Listof Integer)
'(1 2 3 4 5)
> (deque->list (build-deque 5 (λ:([x : Integer]) (* x x))))
- : (Listof Integer)
'(0 1 4 9 16)

procedure
(head+tail deq) → (Pair A (Deque A))
deq : (Deque A)

Function head+tail returns a pair containing the head and the tail of the given deque.

Examples:

> (head+tail (deque 1 2 3 4 5))
- : (Pairof
     Positive-Byte
     #(struct:Deque
       ((Rec
         g299042
         (U (Pairof Positive-Byte g299042) (Promiseof g299042) Null))
        Integer
        (Rec
         g299044
         (U (Pairof Positive-Byte g299044) (Promiseof g299044) Null))
        Integer)))
'(1 . #<Deque>)
> (head+tail (build-deque 5 (λ:([x : Integer]) (* x x))))
- : (Pairof
     Integer
     #(struct:Deque
       ((Rec g299068 (U (Pairof Integer g299068) (Promiseof g299068) Null))
        Integer
        (Rec g299070 (U (Pairof Integer g299070) (Promiseof g299070) Null))
        Integer)))
'(0 . #<Deque>)
> (head+tail (empty Integer))
head+tail: given deque is empty

procedure
(last+init deq) → (Pair A (Deque A))
deq : (Deque A)

Function last+init returns a pair containing the last element and the init of the given deque.

Examples:

> (last+init (deque 1 2 3 4 5))
- : (Pairof
     Positive-Byte
     #(struct:Deque
       ((Rec
         g299111
         (U (Pairof Positive-Byte g299111) (Promiseof g299111) Null))
        Integer
        (Rec
         g299113
         (U (Pairof Positive-Byte g299113) (Promiseof g299113) Null))
        Integer)))
'(5 . #<Deque>)
> (last+init (build-deque 5 (λ:([x : Integer]) (* x x))))
- : (Pairof
     Integer
     #(struct:Deque
       ((Rec g299137 (U (Pairof Integer g299137) (Promiseof g299137) Null))
        Integer
        (Rec g299139 (U (Pairof Integer g299139) (Promiseof g299139) Null))
        Integer)))
'(16 . #<Deque>)
> (last+init (empty Integer))
last+init: given deque is empty

2.2 Implicit Deque🔗ℹ

(require pfds/deque/implicit)

package: pfds

Deques obtained by applying Implicit Recursive Slowdown. Provides amortized running time of O(1) for the operations head, tail, last, init, enqueue-front and enqueue. Implicit Recursive Slowdown combines laziness and technique called Recursive Slow-Down developed by Kaplan and Tarjan in their paper Persistant Lists with Catenation via Recursive Slow-Down.

syntax
(Deque A)

Implicit double ended queue of type A.

procedure
(deque a ...) → (Deque A)
a : A

Function deque creates a Implicit Deque with the given inputs.

Example:

> (deque 1 2 3 4 5 6)
- : (U (Deep Positive-Byte) (Shallow Positive-Byte))
#<Deep>

In the above example, the deque obtained will have 1 as its head element.

value
empty : (Deque Nothing)

An empty deque

procedure
(empty? dq) → Boolean
dq : (Deque A)

Function empty? checks if the given deque is empty or not.

Examples:

> (empty? (deque 1 2 3 4 5 6))
- : Boolean
#f
> (empty? empty)
- : Boolean
#t

procedure
(enqueue a deq) → (Deque A)
a : A
deq : (Deque A)

Function enqueue takes an element and a deque and enqueues the given element into the deque.

Example:

> (enqueue 10 (deque 1 2 3 4 5 6))
- : (U (Deep Positive-Byte) (Shallow Positive-Byte))
#<Deep>

In the above example, enqueue adds the element 10 to (deque 1 2 3 4 5 6 10).

procedure
(enqueue-front a deq) → (Deque A)
a : A
deq : (Deque A)

Function enqueue-front takes an element and a deque and puts the given element to the front of the given deque.

Example:

> (enqueue-front 10 (deque 5 6 3 4))
- : (U (Deep Positive-Byte) (Shallow Positive-Byte))
#<Deep>

In the above example, (enqueue-front 10 (deque 5 6 3 4)) adds 10 to the front of the (deque 5 6 3 4). 10 will be the head element.

procedure
(head deq) → A
deq : (Deque A)

Function head takes a deque and gives the first element in the deque if deque is not empty else throws an error.

Examples:

> (head (deque 1 2 3 4 5 6))
- : Integer [more precisely: Positive-Byte]
1
> (head empty)
head: given deque is empty

procedure
(last deq) → A
deq : (Deque A)

Function last takes a deque and gives the last element in the queue if deque is not empty else throws an error.

Examples:

> (last (deque 1 2 3 4 5 6))
- : Integer [more precisely: Positive-Byte]
6
> (last empty)
last: given deque is empty

procedure
(tail deq) → (Deque A)
deq : (Deque A)

Function tail takes a deque and returns a deque with rest elements if its a non empty deque else throws an error.

Examples:

> (tail (deque 1 2 3 4 5 6))
- : (U (Deep Positive-Byte) (Shallow Positive-Byte))
#<Deep>
> (tail empty)
tail: given deque is empty

In the above example, (tail (deque 1 2 3 4 5 6)), removes 1 and returns (tail (deque 2 3 4 5 6)).

procedure
(init deq) → (Deque A)
deq : (Deque A)

Function init takes a deque and returns a deque without the last element if its a non empty deque else throws an error.

Examples:

> (init (deque 1 2 3 4 5 6))
- : (U (Deep Positive-Byte) (Shallow Positive-Byte))
#<Deep>
> (init empty)
init: given deque is empty

In the above example, (init (deque 1 2 3 4 5 6)), removes the last element 6 and returns (deque 1 2 3 4 5)

procedure
(deque->list deq) → (Listof A)
deq : (Deque A)

Function deque->list takes a deque and returns a list of elements. The list will have head of the given deque as its first element. If the given deque is empty, then it returns an empty list.

Example:

> (deque->list (deque 10 2 34 4 15 6))
- : (Listof Positive-Byte)
'(10 2 34 4 15 6)

procedure
(map func deq1 deq2 ...) → (Deque A)
  func : (A B ... B -> C)
  deq1 : (Deque A)
  deq2 : (Deque B)

Function map is similar to map for lists.

Examples:

> (deque->list (map add1 (deque 1 2 3 4 5 6)))
- : (Listof Positive-Index)
'(2 3 4 5 6 7)
> (deque->list (map * (deque 1 2 3 4 5 6) (deque 1 2 3 4 5 6)))
- : (Listof Positive-Index)
'(1 4 9 16 25 36)

procedure
(foldl func init deq1 deq2 ...) → C
  func : (C A B ... B -> C)
  init : C
  deq1 : (Deque A)
  deq2 : (Deque B)

Function foldl is similar to foldl

foldl currently does not produce correct results when the given function is non-commutative.

Examples:

> (foldl + 0 (deque 1 2 3 4 5 6))
- : Integer [more precisely: Nonnegative-Integer]
21
> (foldl * 1 (deque 1 2 3 4 5 6) (deque 1 2 3 4 5 6))
- : Integer [more precisely: Positive-Integer]
518400

procedure
(foldr func init deq1 deq2 ...) → C
  func : (C A B ... B -> C)
  init : C
  deq1 : (Deque A)
  deq2 : (Deque B)

Function foldr is similar to foldr

foldr currently does not produce correct results when the given function is non-commutative.

Examples:

> (foldr + 0 (deque 1 2 3 4 5 6))
- : Integer [more precisely: Nonnegative-Integer]
21
> (foldr * 1 (deque 1 2 3 4 5 6) (deque 1 2 3 4 5 6))
- : Integer [more precisely: Positive-Integer]
518400

procedure
(filter func que) → (Deque A)
func : (A -> Boolean)
que : (Deque A)

Function filter is similar to filter.

Examples:

> (define que (deque 1 2 3 4 5 6))
> (deque->list (filter (λ: ([x : Integer]) (> x 5)) que))
- : (Listof Positive-Byte)
'(6)
> (deque->list (filter (λ: ([x : Integer]) (< x 5)) que))
- : (Listof Positive-Byte)
'(1 2 3 4)
> (deque->list (filter (λ: ([x : Integer]) (<= x 5)) que))
- : (Listof Positive-Byte)
'(1 2 3 4 5)

procedure
(remove func que) → (Deque A)
func : (A -> Boolean)
que : (Deque A)

Function remove is similar to filter but remove removes the elements which match the predicate.

Examples:

> (deque->list (remove (λ: ([x : Integer]) (> x 5))
                       (deque 1 2 3 4 5 6)))
- : (Listof Positive-Byte)
'(1 2 3 4 5)
> (deque->list (remove (λ: ([x : Integer]) (< x 5))
                       (deque 1 2 3 4 5 6)))
- : (Listof Positive-Byte)
'(5 6)
> (deque->list (remove (λ: ([x : Integer]) (<= x 5))
                       (deque 1 2 3 4 5 6)))
- : (Listof Positive-Byte)
'(6)

procedure
(andmap func deq1 deq2 ...) → Boolean
  func : (A B ... B -> Boolean)
  deq1 : (Deque A)
  deq2 : (Deque B)

Function andmap is similar to andmap.

Examples:

> (andmap even? (deque 1 2 3 4 5 6))
- : Boolean
#f
> (andmap odd? (deque 1 2 3 4 5 6))
- : Boolean
#f
> (andmap positive? (deque 1 2 3 4 5 6))
- : Boolean
#t
> (andmap negative? (deque -1 -2))
- : Boolean
#t

procedure
(ormap func deq1 deq2 ...) → Boolean
  func : (A B ... B -> Boolean)
  deq1 : (Deque A)
  deq2 : (Deque B)

Function ormap is similar to ormap.

Examples:

> (ormap even? (deque 1 2 3 4 5 6))
- : Boolean
#t
> (ormap odd? (deque 1 2 3 4 5 6))
- : Boolean
#t
> (ormap positive? (deque -1 -2 3 4 -5 6))
- : Boolean
#t
> (ormap negative? (deque 1 -2))
- : Boolean
#t

procedure
(build-deque size func) → (Deque A)
size : Natural
func : (Natural -> A)

Function build-deque is similar to build-list.

Examples:

> (deque->list (build-deque 5 (λ:([x : Integer]) (add1 x))))
- : (Listof Integer)
'(1 2 3 4 5)
> (deque->list (build-deque 5 (λ:([x : Integer]) (* x x))))
- : (Listof Integer)
'(0 1 4 9 16)

procedure
(head+tail deq) → (Pair A (Deque A))
deq : (Deque A)

Function head+tail returns a pair containing the head and the tail of the given deque.

Examples:

> (head+tail (deque 1 2 3 4 5))
- : (Pairof Positive-Byte (U (Deep Positive-Byte) (Shallow Positive-Byte)))
'(1 . #<Deep>)
> (head+tail (build-deque 5 (λ:([x : Integer]) (* x x))))
- : (Pairof Integer (U (Deep Integer) (Shallow Integer)))
'(0 . #<Deep>)
> (head+tail empty)
head+tail: given deque is empty

procedure
(last+init deq) → (Pair A (Deque A))
deq : (Deque A)

Function last+init returns a pair containing the last element and the init of the given deque.

Examples:

> (last+init (deque 1 2 3 4 5))
- : (Pairof Positive-Byte (U (Deep Positive-Byte) (Shallow Positive-Byte)))
'(5 . #<Deep>)
> (last+init (build-deque 5 (λ:([x : Integer]) (* x x))))
- : (Pairof Integer (U (Deep Integer) (Shallow Integer)))
'(16 . #<Deep>)
> (last+init empty)
last+init: given deque is empty

2.3 Real-Time Deque🔗ℹ

(require pfds/deque/real-time)

package: pfds

Real-Time Deques eliminate the amortization by using two techniques Scheduling and a variant of Global Rebuilding called Lazy Rebuilding. The data structure gives a worst case running time of O(1) for the operations head, tail, last, init, enqueue-front and enqueue.

syntax
(Deque A)

Real-time double ended queue of type A.

procedure
(deque a ...) → (Deque A)
a : A

Function deque creates a Real-Time Deque with the given inputs.

Example:

> (deque 1 2 3 4 5 6)
- : #(struct:Deque
      ((Rec
        g302784
        (U (Boxof (U (-> (Pairof Integer g302784)) (Pairof Integer g302784)))
           Null))
       Integer
       (Rec
        g302787
        (U (Boxof (U (-> (Pairof Integer g302787)) (Pairof Integer g302787)))
           Null))
       (Rec
        g302790
        (U (Boxof (U (-> (Pairof Integer g302790)) (Pairof Integer g302790)))
           Null))
       Integer
       (Rec
        g302793
        (U (Boxof (U (-> (Pairof Integer g302793)) (Pairof Integer g302793)))
           Null))))
#<Deque>

In the above example, the deque obtained will have 1 as its head element.

procedure
(empty t) → (Deque A)
t : A

An empty deque.

procedure
(empty? dq) → Boolean
dq : (Deque A)

Function empty? checks if the given deque is empty or not.

Examples:

> (empty? (deque 1 2 3 4 5 6))
- : Boolean
#f
> (empty? (empty Integer))
- : Boolean
#t

procedure
(enqueue a deq) → (Deque A)
a : A
deq : (Deque A)

Function enqueue takes an element and a deque and enqueues the given element into the deque.

Example:

> (enqueue 10 (deque 1 2 3 4 5 6))
- : #(struct:Deque
      ((Rec
        g302825
        (U (Boxof (U (-> (Pairof Integer g302825)) (Pairof Integer g302825)))
           Null))
       Integer
       (Rec
        g302828
        (U (Boxof (U (-> (Pairof Integer g302828)) (Pairof Integer g302828)))
           Null))
       (Rec
        g302831
        (U (Boxof (U (-> (Pairof Integer g302831)) (Pairof Integer g302831)))
           Null))
       Integer
       (Rec
        g302834
        (U (Boxof (U (-> (Pairof Integer g302834)) (Pairof Integer g302834)))
           Null))))
#<Deque>

In the above example, enqueue adds the element 10 to the end of (deque 1 2 3 4 5 6).

procedure
(enqueue-front a deq) → (Deque A)
a : A
deq : (Deque A)

Functionenqueue-front takes an element and a deque and adds the given element to the front of deque.

Example:

> (enqueue-front 10 (deque 1 2 3 4 5 6))
- : #(struct:Deque
      ((Rec
        g302846
        (U (Boxof (U (-> (Pairof Integer g302846)) (Pairof Integer g302846)))
           Null))
       Integer
       (Rec
        g302849
        (U (Boxof (U (-> (Pairof Integer g302849)) (Pairof Integer g302849)))
           Null))
       (Rec
        g302852
        (U (Boxof (U (-> (Pairof Integer g302852)) (Pairof Integer g302852)))
           Null))
       Integer
       (Rec
        g302855
        (U (Boxof (U (-> (Pairof Integer g302855)) (Pairof Integer g302855)))
           Null))))
#<Deque>

In the above example, enqueue adds the element 10 to the front of (deque 1 2 3 4 5 6) and returns (deque 10 1 2 3 4 5 6).

procedure
(head deq) → A
deq : (Deque A)

Function head takes a deque and gives the first element in the deque if deque is not empty else throws an error.

Examples:

> (head (deque 1 2 3 4 5 6))
- : Integer
1
> (head (empty Integer))
head: given deque is empty

procedure
(last deq) → A
deq : (Deque A)

Function last takes a deque and gives the last element in the queue if deque is not empty else throws an error.

Examples:

> (last (deque 1 2 3 4 5 6))
- : Integer
6
> (last (empty Integer))
last: given deque is empty

procedure
(tail deq) → (Deque A)
deq : (Deque A)

Function tail takes a deque and returns a deque with rest elements if its a non empty deque else throws an error.

Examples:

> (tail (deque 1 2 3 4 5 6))
- : #(struct:Deque
      ((Rec
        g302905
        (U (Boxof (U (-> (Pairof Integer g302905)) (Pairof Integer g302905)))
           Null))
       Integer
       (Rec
        g302908
        (U (Boxof (U (-> (Pairof Integer g302908)) (Pairof Integer g302908)))
           Null))
       (Rec
        g302911
        (U (Boxof (U (-> (Pairof Integer g302911)) (Pairof Integer g302911)))
           Null))
       Integer
       (Rec
        g302914
        (U (Boxof (U (-> (Pairof Integer g302914)) (Pairof Integer g302914)))
           Null))))
#<Deque>
> (tail (empty Integer))
tail: given deque is empty

In the above example, (tail (deque 1 2 3 4 5 6)), removes the head of the given deque returns (deque 2 3 4 5 6).

procedure
(init deq) → (Deque A)
deq : (Deque A)

Function init takes a deque and returns a deque without the last element if its a non empty deque else throws an error.

Examples:

> (init (deque 1 2 3 4 5 6))
- : #(struct:Deque
      ((Rec
        g302948
        (U (Boxof (U (-> (Pairof Integer g302948)) (Pairof Integer g302948)))
           Null))
       Integer
       (Rec
        g302951
        (U (Boxof (U (-> (Pairof Integer g302951)) (Pairof Integer g302951)))
           Null))
       (Rec
        g302954
        (U (Boxof (U (-> (Pairof Integer g302954)) (Pairof Integer g302954)))
           Null))
       Integer
       (Rec
        g302957
        (U (Boxof (U (-> (Pairof Integer g302957)) (Pairof Integer g302957)))
           Null))))
#<Deque>
> (init (empty Integer))
init: given deque is empty

In the above example, (init (deque 1 2 3 4 5 6)), removes the last element 6 of the given deque and returns (deque 1 2 3 4 5).

procedure
(deque->list deq) → (Listof A)
deq : (Deque A)

Function deque->list takes a deque and returns a list of elements. The list will have head of the given deque as its first element. If the given deque is empty, then it returns an empty list.

Example:

> (deque->list (deque 10 2 34 4 15 6))
- : (Listof Integer)
'(10 2 34 4 15 6)

procedure
(map func deq1 deq2 ...) → (Deque A)
  func : (A B ... B -> C)
  deq1 : (Deque A)
  deq2 : (Deque B)

Function map is similar to map for lists.

Examples:

> (deque->list (map add1 (deque 1 2 3 4 5 6)))
- : (Listof Integer)
'(2 3 4 5 6 7)
> (deque->list (map * (deque 1 2 3 4 5 6) (deque 1 2 3 4 5 6)))
- : (Listof Integer)
'(1 4 9 16 25 36)

procedure
(foldl func init deq1 deq2 ...) → C
  func : (C A B ... B -> C)
  init : C
  deq1 : (Deque A)
  deq2 : (Deque B)

Function foldl is similar to foldl

foldl currently does not produce correct results when the given function is non-commutative.

Examples:

> (foldl + 0 (deque 1 2 3 4 5 6))
- : Integer
21
> (foldl * 1 (deque 1 2 3 4 5 6) (deque 1 2 3 4 5 6))
- : Integer
518400

procedure
(foldr func init deq1 deq2 ...) → C
  func : (C A B ... B -> C)
  init : C
  deq1 : (Deque A)
  deq2 : (Deque B)

Function foldr is similar to foldr

foldr currently does not produce correct results when the given function is non-commutative.

Examples:

> (foldr + 0 (deque 1 2 3 4 5 6))
- : Integer
21
> (foldr * 1 (deque 1 2 3 4 5 6) (deque 1 2 3 4 5 6))
- : Integer
518400

procedure
(filter func que) → (Deque A)
func : (A -> Boolean)
que : (Deque A)

Function filter is similar to filter.

Examples:

> (define que (deque 1 2 3 4 5 6))
> (deque->list (filter (λ: ([x : Integer]) (> x 5)) que))
- : (Listof Integer)
'(6)
> (deque->list (filter (λ: ([x : Integer]) (< x 5)) que))
- : (Listof Integer)
'(1 2 3 4)
> (deque->list (filter (λ: ([x : Integer]) (<= x 5)) que))
- : (Listof Integer)
'(1 2 3 4 5)

procedure
(remove func que) → (Deque A)
func : (A -> Boolean)
que : (Deque A)

Function remove is similar to filter but remove removes the elements which match the predicate.

Examples:

> (deque->list (remove (λ: ([x : Integer]) (> x 5))
                       (deque 1 2 3 4 5 6)))
- : (Listof Integer)
'(1 2 3 4 5)
> (deque->list (remove (λ: ([x : Integer]) (< x 5))
                       (deque 1 2 3 4 5 6)))
- : (Listof Integer)
'(5 6)
> (deque->list (remove (λ: ([x : Integer]) (<= x 5))
                       (deque 1 2 3 4 5 6)))
- : (Listof Integer)
'(6)

procedure
(andmap func deq1 deq2 ...) → Boolean
  func : (A B ... B -> Boolean)
  deq1 : (Deque A)
  deq2 : (Deque B)

Function andmap is similar to andmap.

Examples:

> (andmap even? (deque 1 2 3 4 5 6))
- : Boolean
#f
> (andmap odd? (deque 1 2 3 4 5 6))
- : Boolean
#f
> (andmap positive? (deque 1 2 3 4 5 6))
- : Boolean
#t
> (andmap negative? (deque -1 -2))
- : Boolean
#t

procedure
(ormap func deq1 deq2 ...) → Boolean
  func : (A B ... B -> Boolean)
  deq1 : (Deque A)
  deq2 : (Deque B)

Function ormap is similar to ormap.

Examples:

> (ormap even? (deque 1 2 3 4 5 6))
- : Boolean
#t
> (ormap odd? (deque 1 2 3 4 5 6))
- : Boolean
#t
> (ormap positive? (deque -1 -2 3 4 -5 6))
- : Boolean
#t
> (ormap negative? (deque 1 -2))
- : Boolean
#t

procedure
(build-deque size func) → (Deque A)
size : Natural
func : (Natural -> A)

Function build-deque is similar to build-list.

Examples:

> (deque->list (build-deque 5 (λ:([x : Integer]) (add1 x))))
- : (Listof Integer)
'(1 2 3 4 5)
> (deque->list (build-deque 5 (λ:([x : Integer]) (* x x))))
- : (Listof Integer)
'(0 1 4 9 16)

procedure
(head+tail deq) → (Pair A (Deque A))
deq : (Deque A)

Function head+tail returns a pair containing the head and the tail of the given deque.

Examples:

> (head+tail (deque 1 2 3 4 5))
- : (Pairof
     Integer
     #(struct:Deque
       ((Rec
         g303331
         (U (Boxof (U (-> (Pairof Integer g303331)) (Pairof Integer g303331)))
            Null))
        Integer
        (Rec
         g303334
         (U (Boxof (U (-> (Pairof Integer g303334)) (Pairof Integer g303334)))
            Null))
        (Rec
         g303337
         (U (Boxof (U (-> (Pairof Integer g303337)) (Pairof Integer g303337)))
            Null))
        Integer
        (Rec
         g303340
         (U (Boxof (U (-> (Pairof Integer g303340)) (Pairof Integer g303340)))
            Null)))))
'(1 . #<Deque>)
> (head+tail (build-deque 5 (λ:([x : Integer]) (* x x))))
- : (Pairof
     Integer
     #(struct:Deque
       ((Rec
         g303357
         (U (Boxof (U (-> (Pairof Integer g303357)) (Pairof Integer g303357)))
            Null))
        Integer
        (Rec
         g303360
         (U (Boxof (U (-> (Pairof Integer g303360)) (Pairof Integer g303360)))
            Null))
        (Rec
         g303363
         (U (Boxof (U (-> (Pairof Integer g303363)) (Pairof Integer g303363)))
            Null))
        Integer
        (Rec
         g303366
         (U (Boxof (U (-> (Pairof Integer g303366)) (Pairof Integer g303366)))
            Null)))))
'(0 . #<Deque>)
> (head+tail (empty Integer))
head+tail: given deque is empty

procedure
(last+init deq) → (Pair A (Deque A))
deq : (Deque A)

Function last+init returns a pair containing the last element and the init of the given deque.

Examples:

> (last+init (deque 1 2 3 4 5))
- : (Pairof
     Integer
     #(struct:Deque
       ((Rec
         g303400
         (U (Boxof (U (-> (Pairof Integer g303400)) (Pairof Integer g303400)))
            Null))
        Integer
        (Rec
         g303403
         (U (Boxof (U (-> (Pairof Integer g303403)) (Pairof Integer g303403)))
            Null))
        (Rec
         g303406
         (U (Boxof (U (-> (Pairof Integer g303406)) (Pairof Integer g303406)))
            Null))
        Integer
        (Rec
         g303409
         (U (Boxof (U (-> (Pairof Integer g303409)) (Pairof Integer g303409)))
            Null)))))
'(5 . #<Deque>)
> (last+init (build-deque 5 (λ:([x : Integer]) (* x x))))
- : (Pairof
     Integer
     #(struct:Deque
       ((Rec
         g303426
         (U (Boxof (U (-> (Pairof Integer g303426)) (Pairof Integer g303426)))
            Null))
        Integer
        (Rec
         g303429
         (U (Boxof (U (-> (Pairof Integer g303429)) (Pairof Integer g303429)))
            Null))
        (Rec
         g303432
         (U (Boxof (U (-> (Pairof Integer g303432)) (Pairof Integer g303432)))
            Null))
        Integer
        (Rec
         g303435
         (U (Boxof (U (-> (Pairof Integer g303435)) (Pairof Integer g303435)))
            Null)))))
'(16 . #<Deque>)
> (last+init (empty Integer))
last+init: given deque is empty

1	Queues
2	Deques
3	Heaps
4	Random Access Lists
5	VList
6	Streams
7	Red-Black Trees
8	Tries
9	Treap