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Singly-linked list/Traversal

From Rosetta Code
Task
Singly-linked list/Traversal
You are encouraged to solve this task according to the task description, using any language you may know.

Traverse from the beginning of a singly-linked list to the end.


See also



AArch64 Assembly[edit]

Works with: as version Raspberry Pi 3B version Buster 64 bits
 
/* ARM assembly AARCH64 Raspberry PI 3B */
/* program afficheList64.s */
 
/*******************************************/
/* Constantes file */
/*******************************************/
/* for this file see task include a file in language AArch64 assembly*/
.include "../includeConstantesARM64.inc"
 
.equ NBELEMENTS, 100 // list size
 
/*******************************************/
/* Structures */
/********************************************/
/* structure linkedlist*/
.struct 0
llist_next: // next element
.struct llist_next + 8
llist_value: // element value
.struct llist_value + 8
llist_fin:
/* Initialized data */
.data
szMessInitListe: .asciz "List initialized.\n"
szCarriageReturn: .asciz "\n"
/* datas error display */
szMessErreur: .asciz "Error detected.\n"
/* datas message display */
szMessResult: .asciz "Element No : @ value @ \n"
 
/* UnInitialized data */
.bss
lList1: .skip llist_fin * NBELEMENTS // list memory place
sZoneConv: .skip 100
/* code section */
.text
.global main
main:
ldr x0,qAdrlList1
mov x1,#0 // list init
str x1,[x0,#llist_next]
ldr x0,qAdrszMessInitListe
bl affichageMess
ldr x0,qAdrlList1
mov x1,#2
bl insertElement // add element value 2
ldr x0,qAdrlList1
mov x1,#5
bl insertElement // add element value 5
// // display elements of list
ldr x3,qAdrlList1
mov x2,#0 // ident element
1:
ldr x0,[x3,#llist_next] // end list ?
cmp x0,#0
beq 100f // yes
add x2,x2,#1
mov x0,x2 // display No element and value
ldr x1,qAdrsZoneConv
bl conversion10S
ldr x0,qAdrszMessResult
ldr x1,qAdrsZoneConv
bl strInsertAtCharInc
mov x5,x0 // address of new string
ldr x0,[x3,#llist_value]
ldr x1,qAdrsZoneConv
bl conversion10S
mov x0,x5 // new address of message
ldr x1,qAdrsZoneConv
bl strInsertAtCharInc
bl affichageMess
ldr x3,[x3,#llist_next] // next element
b 1b // and loop
100: // standard end of the program
mov x8, #EXIT // request to exit program
svc 0 // perform system call
qAdrszMessInitListe: .quad szMessInitListe
qAdrszMessErreur: .quad szMessErreur
qAdrszCarriageReturn: .quad szCarriageReturn
qAdrlList1: .quad lList1
qAdrszMessResult: .quad szMessResult
qAdrsZoneConv: .quad sZoneConv
 
/******************************************************************/
/* insert element at end of list */
/******************************************************************/
/* x0 contains the address of the list */
/* x1 contains the value of element */
/* x0 returns address of element or - 1 if error */
insertElement:
stp x1,lr,[sp,-16]! // save registers
stp x2,x3,[sp,-16]! // save registers
mov x2,#llist_fin * NBELEMENTS
add x2,x2,x0 // compute address end list
1: // start loop
ldr x3,[x0,#llist_next] // load next pointer
cmp x3,#0 // = zero
csel x0,x3,x0,ne
bne 1b // no -> loop with pointer
add x3,x0,#llist_fin // yes -> compute next free address
cmp x3,x2 // > list end
bge 99f // yes -> error
str x3,[x0,#llist_next] // store next address in current pointer
str x1,[x0,#llist_value] // store element value
mov x1,#0
str x1,[x3,#llist_next] // init next pointer in next address
b 100f
99: // error
mov x0,-1
100:
ldp x2,x3,[sp],16 // restaur 2 registers
ldp x1,lr,[sp],16 // restaur 2 registers
ret // return to address lr x30
/********************************************************/
/* File Include fonctions */
/********************************************************/
/* for this file see task include a file in language AArch64 assembly */
.include "../includeARM64.inc"
 
 

ACL2[edit]

The standard list data type is a singly linked list.

(defun traverse (xs)
(if (endp xs)
(cw "End.~%")
(prog2$ (cw "~x0~%" (first xs))
(traverse (rest xs)))))

Action![edit]

The user must type in the monitor the following command after compilation and before running the program!
SET EndProg=*
CARD EndProg ;required for ALLOCATE.ACT
 
INCLUDE "D2:ALLOCATE.ACT" ;from the Action! Tool Kit. You must type 'SET EndProg=*' from the monitor after compiling, but before running this program!
 
DEFINE PTR="CARD"
DEFINE NODE_SIZE="4"
TYPE ListNode=[INT data PTR nxt]
 
ListNode POINTER listBegin
 
PTR FUNC FindLast()
ListNode POINTER last
 
last=listBegin
IF last=0 THEN
RETURN (0)
FI
WHILE last.nxt#0
DO
last=last.nxt
OD
RETURN (last)
 
PROC Append(INT v)
ListNode POINTER n,last
 
n=Alloc(NODE_SIZE)
n.data=v
n.nxt=0
last=FindLast()
IF last THEN
last.nxt=n
ELSE
listBegin=n
FI
RETURN
 
PROC Clear()
ListNode POINTER n,next
 
n=listBegin
WHILE n
DO
next=n.nxt
Free(n,NODE_SIZE)
n=next
OD
listBegin=0
RETURN
 
PROC Traverse()
ListNode POINTER n
 
n=listBegin
PrintE("Traverse:")
Print("(")
WHILE n
DO
PrintI(n.data)
IF n.nxt THEN
Print(", ")
FI
n=n.nxt
OD
PrintE(")")
RETURN
 
PROC Main()
INT i
Put(125) PutE() ;clear screen
 
AllocInit(0)
listBegin=0
 
FOR i=0 TO 50
DO
Append(i*i)
OD
Traverse()
 
Clear()
RETURN
Output:

Screenshot from Atari 8-bit computer

Traverse:
(0, 1, 4, 9, 16, 25, 36, 49, 64, 81, 100, 121, 144, 169, 196, 225, 256, 289, 324, 361, 400, 441, 484, 529, 576, 625, 676, 729, 784, 841, 900, 961, 1024, 1089, 1156, 1225, 1296, 1369, 1444, 1521, 1600, 1681, 1764, 1849, 1936, 2025, 2116, 2209, 2304, 2401, 2500)

ActionScript[edit]

See Singly-Linked List (element) in ActionScript

var A:Node;
//...
for(var i:Node = A; i != null; i = i.link)
{
doStuff(i);
}

Ada[edit]

The Ada standard container library provides a doubly-linked list. List traversal is demonstrated for the forward links.

with Ada.Containers.Doubly_Linked_Lists;
with Ada.Text_Io; use Ada.Text_Io;
 
procedure Traversal_Example is
package Int_List is new Ada.Containers.Doubly_Linked_Lists(Integer);
use Int_List;
procedure Print(Position : Cursor) is
begin
Put_Line(Integer'Image(Element(Position)));
end Print;
The_List : List;
begin
for I in 1..10 loop
The_List.Append(I);
end loop;
-- Traverse the list, calling Print for each value
The_List.Iterate(Print'access);
end traversal_example;

ALGOL 68[edit]

Works with: ALGOL 68 version Revision 1 - no extensions to language used
Works with: ALGOL 68G version Any - tested with release 1.18.0-9h.tiny
Works with: ELLA ALGOL 68 version Any (with appropriate job cards) - tested with release 1.8-8d

Linked lists are not built into ALGOL 68 per se, nor any available standard library. However Linked lists are presented in standard text book examples. Or can be manually constructed, eg:

MODE STRINGLIST = STRUCT(STRING value, REF STRINGLIST next);
 
STRINGLIST list := ("Big",
LOC STRINGLIST := ("fjords",
LOC STRINGLIST := ("vex",
LOC STRINGLIST := ("quick",
LOC STRINGLIST := ("waltz",
LOC STRINGLIST := ("nymph",NIL))))));
 
REF STRINGLIST node := list;
WHILE node ISNT REF STRINGLIST(NIL) DO
print((value OF node, space));
node := next OF node
OD;
print(newline)
Output:
Big fjords vex quick waltz nymph

ALGOL W[edit]

begin
 % record type to hold a singly linked list of integers  %
record ListI ( integer iValue; reference(ListI) next );
 
 % inserts a new value after the specified element of a list  %
procedure insert( reference(ListI) value list
 ; integer value newValue
) ;
next(list) := ListI( newValue, next(list) );
 
 % declare variables to hold the list  %
reference(ListI) head, pos;
 
 % create a list of integers  %
head := ListI( 1701, ListI( 9000, ListI( 42, ListI( 90210, null ) ) ) );
 
 % insert a new value into the list  %
insert( next(head), 4077 );
 
 % traverse the list  %
pos := head;
 
while pos not = null do begin
write( iValue(pos) );
pos := next(pos);
end;
 
end.
Output:
          1701  
          9000  
          4077  
            42  
         90210  

ARM Assembly[edit]

Works with: as version Raspberry Pi
 
/* ARM assembly Raspberry PI */
/* program afficheList.s */
 
/* Constantes */
.equ STDOUT, 1 @ Linux output console
.equ EXIT, 1 @ Linux syscall
.equ READ, 3
.equ WRITE, 4
 
.equ NBELEMENTS, 100 @ list size
 
/*******************************************/
/* Structures */
/********************************************/
/* structure linkedlist*/
.struct 0
llist_next: @ next element
.struct llist_next + 4
llist_value: @ element value
.struct llist_value + 4
llist_fin:
/* Initialized data */
.data
szMessInitListe: .asciz "List initialized.\n"
szCarriageReturn: .asciz "\n"
/* datas error display */
szMessErreur: .asciz "Error detected.\n"
/* datas message display */
szMessResult: .ascii "Element No :"
sNumElement: .space 12,' '
.ascii " value : "
sValue: .space 12,' '
.asciz "\n"
 
/* UnInitialized data */
.bss
lList1: .skip llist_fin * NBELEMENTS @ list memory place
/* code section */
.text
.global main
main:
ldr r0,iAdrlList1
mov r1,#0 @ list init
str r1,[r0,#llist_next]
ldr r0,iAdrszMessInitListe
bl affichageMess
ldr r0,iAdrlList1
mov r1,#2
bl insertElement @ add element value 2
ldr r0,iAdrlList1
mov r1,#5
bl insertElement @ add element value 5
@ @ display elements of list
ldr r3,iAdrlList1
mov r2,#0 @ ident element
1:
ldr r0,[r3,#llist_next] @ end list ?
cmp r0,#0
beq 100f @ yes
add r2,#1
mov r0,r2 @ display No element and value
ldr r1,iAdrsNumElement
bl conversion10S
ldr r0,[r3,#llist_value]
ldr r1,iAdrsValue
bl conversion10S
ldr r0,iAdrszMessResult
bl affichageMess
ldr r3,[r3,#llist_next] @ next element
b 1b @ and loop
100: @ standard end of the program
mov r7, #EXIT @ request to exit program
svc 0 @ perform system call
iAdrszMessInitListe: .int szMessInitListe
iAdrszMessErreur: .int szMessErreur
iAdrszCarriageReturn: .int szCarriageReturn
iAdrlList1: .int lList1
iAdrszMessResult: .int szMessResult
iAdrsNumElement: .int sNumElement
iAdrsValue: .int sValue
 
/******************************************************************/
/* insert element at end of list */
/******************************************************************/
/* r0 contains the address of the list */
/* r1 contains the value of element */
/* r0 returns address of element or - 1 if error */
insertElement:
push {r1-r3,lr} @ save registers
mov r2,#llist_fin * NBELEMENTS
add r2,r0 @ compute address end list
1: @ start loop
ldr r3,[r0,#llist_next] @ load next pointer
cmp r3,#0 @ = zero
movne r0,r3 @ no -> loop with pointer
bne 1b
add r3,r0,#llist_fin @ yes -> compute next free address
cmp r3,r2 @ > list end
movge r0,#-1 @ yes -> error
bge 100f
str r3,[r0,#llist_next] @ store next address in current pointer
str r1,[r0,#llist_value] @ store element value
mov r1,#0
str r1,[r3,#llist_next] @ init next pointer in next address
 
100:
pop {r1-r3,lr} @ restaur registers
bx lr @ return
/******************************************************************/
/* display text with size calculation */
/******************************************************************/
/* r0 contains the address of the message */
affichageMess:
push {r0,r1,r2,r7,lr} @ save registers
mov r2,#0 @ counter length */
1: @ loop length calculation
ldrb r1,[r0,r2] @ read octet start position + index
cmp r1,#0 @ if 0 its over
addne r2,r2,#1 @ else add 1 in the length
bne 1b @ and loop
@ so here r2 contains the length of the message
mov r1,r0 @ address message in r1
mov r0,#STDOUT @ code to write to the standard output Linux
mov r7, #WRITE @ code call system "write"
svc #0 @ call system
pop {r0,r1,r2,r7,lr} @ restaur registers
bx lr @ return
/***************************************************/
/* Converting a register to a signed decimal */
/***************************************************/
/* r0 contains value and r1 area address */
conversion10S:
push {r0-r4,lr} @ save registers
mov r2,r1 @ debut zone stockage
mov r3,#'+' @ par defaut le signe est +
cmp r0,#0 @ negative number ?
movlt r3,#'-' @ yes
mvnlt r0,r0 @ number inversion
addlt r0,#1
mov r4,#10 @ length area
1: @ start loop
bl divisionpar10U
add r1,#48 @ digit
strb r1,[r2,r4] @ store digit on area
sub r4,r4,#1 @ previous position
cmp r0,#0 @ stop if quotient = 0
bne 1b
 
strb r3,[r2,r4] @ store signe
subs r4,r4,#1 @ previous position
blt 100f @ if r4 < 0 -> end
 
mov r1,#' ' @ space
2:
strb r1,[r2,r4] @store byte space
subs r4,r4,#1 @ previous position
bge 2b @ loop if r4 > 0
100:
pop {r0-r4,lr} @ restaur registers
bx lr
/***************************************************/
/* division par 10 unsigned */
/***************************************************/
/* r0 dividende */
/* r0 quotient */
/* r1 remainder */
divisionpar10U:
push {r2,r3,r4, lr}
mov r4,r0 @ save value
//mov r3,#0xCCCD @ r3 <- magic_number lower raspberry 3
//movt r3,#0xCCCC @ r3 <- magic_number higter raspberry 3
ldr r3,iMagicNumber @ r3 <- magic_number raspberry 1 2
umull r1, r2, r3, r0 @ r1<- Lower32Bits(r1*r0) r2<- Upper32Bits(r1*r0)
mov r0, r2, LSR #3 @ r2 <- r2 >> shift 3
add r2,r0,r0, lsl #2 @ r2 <- r0 * 5
sub r1,r4,r2, lsl #1 @ r1 <- r4 - (r2 * 2) = r4 - (r0 * 10)
pop {r2,r3,r4,lr}
bx lr @ leave function
iMagicNumber: .int 0xCCCCCCCD
 

ATS[edit]

I repeated the ‘Rosetta Code linear list type’ here, so you can simply copy the code below, compile it, and run it.

Also I put the executable parts in initialization rather than the main program, to avoid being forced to ‘consume’ the list (free its memory). I felt that would be a distraction.

The traversal function is proven to terminate.

(*------------------------------------------------------------------*)
 
(* The Rosetta Code linear list type can contain any [email protected]
(The ‘@’ means it doesn’t have to be the size of a pointer.
You can read {0 <= n} as ‘for all non-negative n’. *)
dataviewtype rclist_vt (vt : [email protected]+, n : int) =
| rclist_vt_nil (vt, 0)
| {0 <= n} rclist_vt_cons (vt, n + 1) of (vt, rclist_vt (vt, n))
 
(* A lemma one will need: lists never have negative lengths. *)
extern prfun {vt : [email protected]}
lemma_rclist_vt_param
{n : int}
(lst : !rclist_vt (vt, n)) :<prf> [0 <= n] void
 
(* Proof of the lemma. *)
primplement {vt}
lemma_rclist_vt_param lst =
case+ lst of
| rclist_vt_nil () => ()
| rclist_vt_cons _ => ()
 
(*------------------------------------------------------------------*)
 
(* For simplicity, the Rosetta Code linear list traverse-and-print
routine will be specifically for lists of ‘int’. *)
 
(* Some things that will be needed. *)
#include "share/atspre_staload.hats"
 
(* The list is passed by value and will be preserved with the same
type. *)
extern fun
rclist_int_traverse_and_print
{m  : int} (* ‘for all list lengths m’ *)
(lst : !rclist_vt (int, m) >> (* ! = pass by value *)
(* The new type will be the same as the old
type. *)
rclist_vt (int, m)) : void
 
implement
rclist_int_traverse_and_print {m} (lst) =
{
(* A recursive nested function that traverses the list, printing
elements along the way. *)
fun
traverse {k : int | 0 <= k}
.<k>. (* Means: ‘k must uniformly decrease towards zero.’
If so, that is proof that ‘find’ terminates. *)
(lst : !rclist_vt (int, k) >> rclist_vt (int, k)) :
void =
case+ lst of
| rclist_vt_nil () => () (* End of list. *)
| rclist_vt_cons (head, tail) =>
begin
println! (head);
traverse tail
end
 
(* The following is needed to prove that the initial k above
satisfies 0 <= k. *)
prval _ = lemma_rclist_vt_param lst
 
val _ = traverse lst
}
 
(* Now let’s try it. *)
 
(* Some convenient notation. *)
#define NIL rclist_vt_nil ()
#define :: rclist_vt_cons
overload traverse_and_print with rclist_int_traverse_and_print
 
val A = 123
val B = 789
val C = 456
 
val lst = A :: C :: B :: NIL
 
val () = traverse_and_print lst
 
(*------------------------------------------------------------------*)
 
implement
main0 () = ()
Output:
$ patscc -DATS_MEMALLOC_LIBC singly_linked_list_traversal.dats && ./a.out
123
456
789

AutoHotkey[edit]

a = 1
a_next = b
b = 2
b_next = c
c = 3
 
traverse("a")
return
 
traverse(element)
{
MsgBox % element . "= " . %element%
name := element . "_next"
while, %name%
{
element := %name%
msgbox % %name% . "= " . %element%
name := %name% . "_next"
}
}

Axe[edit]

LINK(L₁,1)→A
LINK(L₁+10,2)→B
LINK(L₁+50,3)→C
 
INSERT(A,B)
INSERT(A,C)
 
A→I
While I≠0
Disp VALUE(I)▶Dec,i
NEXT(I)→I
End

BBC BASIC[edit]

      DIM node{pNext%, iData%}
DIM a{} = node{}, b{} = node{}, c{} = node{}
 
a.pNext% = b{}
a.iData% = 123
b.iData% = 789
c.iData% = 456
 
PROCinsert(a{}, c{})
 
PRINT "Traverse list:"
pnode% = a{}
REPEAT
 !(^node{}+4) = pnode%
PRINT node.iData%
pnode% = node.pNext%
UNTIL pnode% = 0
 
END
 
DEF PROCinsert(here{}, new{})
new.pNext% = here.pNext%
here.pNext% = new{}
ENDPROC
 
Output:
Traverse list:
       123
       456
       789

C[edit]

See Singly-Linked List (element) in C.

struct link *first;
// ...
struct link *iter;
for(iter = first; iter != NULL; iter = iter->next) {
// access data, e.g. with iter->data
}

C#[edit]

Uses the generic version of the node type located here.

var current = [head of list to traverse]
while(current != null)
{
// Do something with current.Value.
 
current = current.Next;
}

Alternatively, as a for loop:

for (var current = [head of list to traverse]; current != null; current = current.Next)
{
// Do something with current.Value.
}

C++[edit]

Works with: C++11

For each traversal version.

#include <iostream>
#include <forward_list>
 
int main()
{
std::forward_list<int> list{1, 2, 3, 4, 5};
for (int e : list)
std::cout << e << std::endl;
}

Clojure[edit]

(doseq [x xs] (println x))

Common Lisp[edit]

(dolist (x list)
(print x))

Using LOOP:

(loop for x in list do (print x))

Using MAPC

(mapc #'print list)

Using MAP

(map nil #'print list)


Not using builtin list iteration:

(loop for ref = list then (rest ref)
until (null ref)
do (print (first ref)))

Computer/zero Assembly[edit]

A linked list can be implemented as a chain of CONS cells, where each cell is made up of two neighbouring memory locations: the CAR, storing an item of data, and the CDR, storing the address of the next cell in the list. The CDR of the last cell contains not an address but a special NIL value that is guaranteed not to be a valid address; in this implementation, we use 0 to represent NIL. The order of CONS cells in memory is of course entirely unimportant. For the sake of example, this program traverses the list '(1 2 3 4 5 6) and halts with the final value in the accumulator. The program is reasonably straightforward, but it does make some use of instruction arithmetic (self-modifying code).

start:  LDA  load
ADD car  ; head of list
STA ldcar
 
ADD one
STA ldcdr
 
ldcar: NOP
STA value
 
ldcdr: NOP
BRZ done  ; 0 == NIL
STA car
 
JMP start
 
done: LDA value
STP
 
load: LDA 0
value: 0
car: 28  ; head of list
one: 1
 
20,21: 6, 0
22,23: 2, 26
24,25: 5, 20
26,27: 3, 30
28,29: 1, 22
30,31: 4, 24

D[edit]

struct SLinkedNode(T) {
T data;
typeof(this)* next;
}
 
void main() {
import std.stdio;
 
alias N = SLinkedNode!int;
auto lh = new N(1, new N(2, new N(3, new N(4))));
 
for (auto p = lh; p; p = p.next)
write(p.data, " ");
writeln();
}
Output:
1 2 3 4 

Alternative Version[edit]

Using tango's collections (written by Doug Lea, ported to D):

import tango.io.Stdout;
import tango.util.collection.LinkSeq;
 
void main() {
auto m = new LinkSeq!(char[]);
m.append("alpha");
m.append("bravo");
m.append("charlie");
foreach (val; m)
Stdout(val).newline;
}

Delphi[edit]

uses system ;
 
type
 
// declare the list pointer type
plist = ^List ;
 
// declare the list type, a generic data pointer prev and next pointers
List = record
data : pointer ;
next : pList ;
end;
 
// since this task is just showing the traversal I am not allocating the memory and setting up the root node etc.
// Note the use of the carat symbol for de-referencing the pointer.
 
begin
 
// beginning to end
while not (pList^.Next = NIL) do pList := pList^.Next ;
 
end;

Dyalect[edit]

Dyalect doesn't support linked lists out of the box, but it is fairly simple to implement one:

type List = Cons(value, tail) or Nil()
with Lookup
 
static func List.FromArray(xs) {
var list = List.Nil()
var len = xs.Length()
 
for i in (len-1)^-1..0 {
list = List.Cons(xs[i], list)
}
 
return list
}
 
func List.Iterate() {
var xs = this
do {
match xs {
Cons(value, tail) => {
yield value
xs = tail
},
Nil() => {
yield break
}
}
 
} while true
}
 
var xs = List.FromArray([1..10])
 
for x in xs {
print(x)
}

It is also possible to provide an ad hoc solution to the problem:

Translation of: E
var xs = (1, (2, (3, (4, (5, (6, (7, (8, (9, (10, nil))))))))))
 
while xs is (value, tail) {
print(value)
xs = tail
}

Here a linked list is emulated using tuples.

E[edit]

Using a list made from tuples:

var linkedList := [1, [2, [3, [4, [5, [6, [7, null]]]]]]]
 
while (linkedList =~ [value, next]) {
println(value)
linkedList := next
}

Using a list made from the structure defined at Singly-Linked List (element):

var linkedList := makeLink(1, makeLink(2, makeLink(3, empty)))
 
while (!(linkedList.null())) {
println(linkedList.value())
linkedList := linkedList.next()
}

EchoLisp[edit]

Lists - linked-lists - are the fundamental data type in EchoLisp. A lot of fuctions exist to scan lists or operate on successive elements.

 
(define friends '( albert ludwig elvis 🌀))
 
(for-each write friends)→ albert ludwig elvis 🌀
 
; for loop
(for ((friend friends)) (write friend)) → albert ludwig elvis 🌀
 
; map a function
(map string-upcase friends)("ALBERT" "LUDWIG" "ELVIS" "🌀")
(map string-randcase friends)("ALBerT" "LudWIG" "elVis" "🌀")
 
; recursive way
(define (rscan L)
(unless (null? L)
(write (first L))
(rscan (rest L))))
 
(rscan friends) → albert ludwig elvis 🌀
 
; folding a list
; check that ∑ 1..n = n (n+1)/2
 
(define L (iota 1001))
(foldl + 0 L)500500 ; 1000 * 1001 / 2
 
 

Ela[edit]

traverse [] = []
traverse (x::xs) = x :: traverse xs

This function traverses a list and constructs a new list at the same time. For a list in Ela it is the same as identity function, e.g. traverse [1,2,3] == [1,2,3]. However it can be useful in some cases. For example, to enforce a lazy list:

xs = [& x \\ x <- [1..1000]]//lazy list
 
traverse xs

Elena[edit]

Simple iteration with a while loop.

 
while(nil != current){
console printLine(current.Item);
current := current.Next
}

Erlang[edit]

Use built in functions like lists:map/2 and lists:foldl/3.

1> lists:map( fun erlang:is_integer/1, [1,2,3,a,b,c] ).
[true,true,true,false,false,false]
4> lists:foldl( fun erlang:'+'/2, 0, [1,2,3] ).
6

Factor[edit]

: list-each ( linked-list quot: ( data -- ) -- )
[ [ data>> ] dip call ]
[ [ next>> ] dip over [ list-each ] [ 2drop ] if ] 2bi ; inline recursive
 
SYMBOLS: A B C ;
 
A <linked-list>
[ C <linked-list> list-insert ] keep
[ B <linked-list> list-insert ] keep
 
[ . ] list-each
Output:
A
B
C

Fantom[edit]

Using the definitions from Singly-Linked_List_(element_insertion):

    // traverse the linked list
Node? current := a
while (current != null)
{
echo (current.value)
current = current.successor
}

Forth[edit]

: last ( list -- end )
begin dup @ while @ repeat ;

And here is a function to walk a list, calling an XT on each data cell:

: walk ( a xt -- )
>r begin ?dup while
dup cell+ @ [email protected] execute
@ repeat r> drop ;

Testing code:

A ' emit walk ABC ok

Fortran[edit]

Fortran 95. See Singly-Linked List (element) in Fortran.

subroutine traversal(list,proc)
type(node), target :: list
type(node), pointer :: current
interface
subroutine proc(node)
real, intent(in) :: node
end subroutine proc
end interface
current => list
do while ( associated(current) )
call proc(current%data)
current => current%next
end do
end subroutine traversal

Print data from all nodes of a singly-linked list:

subroutine printNode(data)
real, intent(in) :: data
write (*,*) data
end subroutine
 
subroutine printAll(list)
type(node), intent(in) :: list
call traversal(list,printNode)
end subroutine printAll

FreeBASIC[edit]

Requires the type definition and node insertion routine here and here respectively. Also includes a routine for allocating space for a node.

#define NULL 0
 
function alloc_ll_int( n as integer ) as ll_int ptr
dim as ll_int ptr ret = allocate(sizeof(ll_int))
ret->n = n
ret->nxt = NULL
return ret
end function
 
sub traverse_ll_int( head as ll_int ptr )
dim as ll_int ptr curr = head
while curr <> NULL
print curr->n
curr = curr->nxt
wend
end sub
 
dim as ll_int ptr curr, head = alloc_ll_int( 0 ), node
dim as integer i
curr=head
for i = 1 to 50
'build a list to traverse. This is basically a traversal itself...
node = alloc_ll_int( i )
insert_ll_int( curr, node )
curr = curr->nxt
next i
 
traverse_ll_int( head )

Go[edit]

See Singly-Linked List (element) in Go.

start := &Ele{"tacos", nil}
end := start.Append("burritos")
end = end.Append("fajitas")
end = end.Append("enchilatas")
for iter := start; iter != nil; iter = iter.Next {
fmt.Println(iter)
}

Haskell[edit]

Lists are ubiquitous in Haskell, simply use Haskell's map library function:

map (>5) [1..10] -- [False,False,False,False,False,True,True,True,True,True]
 
map (++ "s") ["Apple", "Orange", "Mango", "Pear"] -- ["Apples","Oranges","Mangos","Pears"]
 
foldr (+) 0 [1..10] -- prints 55
 
traverse :: [a] -> [a]
traverse list = map func list
where func a = -- ...do something with a

Note that the traverse function is polymorphic; denoted by traverse :: [a] -> [a] where a can be of any type.

Icon and Unicon[edit]

Using either the record or class-based definitions from Singly-Linked List (element) in Icon and Unicon:

procedure main ()
ns := Node(1, Node(2, Node (3)))
until /ns do { # repeat until ns is null
write (ns.value)
ns := ns.successor
}
end

Prints the numbers 1, 2, 3 in turn.

J[edit]

Using the implementation mentioned at Singly-Linked List (element) in J, we can apply a function foo to each node the following way:

foo"0 {:"1 list

Java[edit]

Works with: Java version 1.5+

For Java.util.LinkedList<T>, use a for each loop (from Loop Structures):

LinkedList<Type> list = new LinkedList<Type>();
 
for(Type i: list){
//each element will be in variable "i"
System.out.println(i);
}

Note that java.util.LinkedList can also perform as a stack, queue, or doubly-linked list.

JavaScript[edit]

Extending Singly-Linked_List_(element)#JavaScript

LinkedList.prototype.traverse = function(func) {
func(this);
if (this.next() != null)
this.next().traverse(func);
}
 
LinkedList.prototype.print = function() {
this.traverse( function(node) {print(node.value())} );
}
 
var head = createLinkedListFromArray([10,20,30,40]);
head.print();

Uses the print() function from Rhino


Alternatively, translating the Haskell examples in terms of JavaScript's Array.map, Array.reduce, and Array.forEach:

var map = function (fn, list) {
return list.map(fn);
},
 
foldr = function (fn, acc, list) {
var listr = list.slice();
listr.reverse();
 
return listr.reduce(fn, acc);
},
 
traverse = function (list, fn) {
return list.forEach(fn);
};
 
var range = function (m, n) {
return Array.apply(null, Array(n - m + 1)).map(
function (x, i) {
return m + i;
}
);
};
 
// --> [false, false, false, false, false, true, true, true, true, true]
map(function (x) {
return x > 5;
}, range(1, 10));
 
// --> ["Apples", "Oranges", "Mangos", "Pears"]
map(function (x) {
return x + 's';
}, ["Apple", "Orange", "Mango", "Pear"])
 
// --> 55
foldr(function (acc, x) {
return acc + x;
}, 0, range(1, 10))
 
 
traverse(["Apple", "Orange", "Mango", "Pear"], function (x) {
console.log(x);
})
/* Apple */
/* Orange */
/* Mango */
/* Pear */

jq[edit]

Works with: jq

Works with gojq, the Go implementation of jq

For context see Singly-linked_list/Element_definition#jq.

Here we define a "map" filter as well as a traversal filter. The "map" filter is similar to the built-in `map` in that it can be used to remove items as per the comment below.

 
# Produce a stream of the items in the input SLL.
def items:
while(.; .next) | .item;
 
def to_singly_linked_list(s):
reduce ([s]|reverse[]) as $item (null; {$item, next:.});
 
# If f evaluates to empty at any item, that item is removed;
# if f evaluates to more than one item, all are added separately.
def map_singly_linked_list(f): to_singly_linked_list( items | f );

Examples

{
"item": 1,
"next": {
"item": 2,
"next": null
}
}
| reduce items as $item (null; .+$item),
map_singly_linked_list(- .)
Output:
3
{
  "item": -1,
  "next": {
    "item": -2,
    "next": null
  }
}

Julia[edit]

Works with: Julia version 0.6

Julia let you implement list traversal very easily: see Singly-linked_list/Element_definition#Julia for the LinkedList struct definition.

Base.start(ll::LinkedList) = ll.head
Base.done(ll::LinkedList{T}, st::AbstractNode{T}) where T = st isa EmptyNode
Base.next(ll::LinkedList{T}, st::AbstractNode{T}) where T = st.data, st.next
 
lst = LinkedList{Int}()
push!(lst, 1)
push!(lst, 2)
push!(lst, 3)
 
for n in lst
print(n, " ")
end

Kotlin[edit]

Lists in Kotlin may be instanciated from Java classes or from Kotlin methods or extensions.

fun main(args: Array<String>) {
val list = IntRange(1, 50).toList()
 
// classic traversal:
for (i in list) { print("%4d ".format(i)); if (i % 10 == 0) println() }
 
// list iterator:
list.asReversed().forEach { print("%4d ".format(it)); if (it % 10 == 1) println() }
}
Output:
   1    2    3    4    5    6    7    8    9   10 
  11   12   13   14   15   16   17   18   19   20 
  21   22   23   24   25   26   27   28   29   30 
  31   32   33   34   35   36   37   38   39   40 
  41   42   43   44   45   46   47   48   49   50 
  50   49   48   47   46   45   44   43   42   41 
  40   39   38   37   36   35   34   33   32   31 
  30   29   28   27   26   25   24   23   22   21 
  20   19   18   17   16   15   14   13   12   11 
  10    9    8    7    6    5    4    3    2    1

Limbo[edit]

Lists are a built-in type in Limbo.

implement Command;
 
include "sys.m";
sys: Sys;
 
include "draw.m";
 
include "sh.m";
 
init(nil: ref Draw->Context, nil: list of string)
{
sys = load Sys Sys->PATH;
 
l := list of {1, 2, 3, 4, 5};
 
# the unary 'tl' operator gets the tail of a list
for (; l != nil; l = tl l)
sys->print("%d\n", hd l);
# the unary 'hd' operator gets the head of a list
}

[edit]

LAST is already a Logo built-in, but it could be defined this way:

to last :list
if empty? bf :list [output first :list]
output last bf :list
end

Logtalk[edit]

The built-in list type can be viewed as a singly linked list. Traversing can be trivially done using a tail-recursive predicate:

 
:- object(singly_linked_list).
 
:- public(show/0).
 
show :-
traverse([1,2,3]).
 
traverse([]).
traverse([Head| Tail]) :-
write(Head), nl,
traverse(Tail).
 
:- end_object.
 
Output:
 
| ?- singly_linked_list::show.
1
2
3
yes
 

Mathematica/Wolfram Language[edit]

Print /@ {"rosettacode", "kitten", "sitting", "rosettacode",  "raisethysword"}
Output:
rosettacode
kitten
sitting
rosettacode
raisethysword

MATLAB / Octave[edit]

Matlab and Octave do not have pointers. Linked lists are implemented as vectors (i.e. arrays of size 1xN)

list = 1:10; 
for k=1:length(list)
printf('%i\n',list(k))
end;

It is recommended to avoid loops and "vectorize" the code:

  printf('%d\n', list(:));    

MiniScript[edit]

We're choosing here to use the built-in list type, rather than make our own from scratch, since this is more representative of how one is likely to actually use MiniScript.

myList = [2, 4, 6, 8]
for i in myList
print i
end for
Output:
2
4
6
8

Nanoquery[edit]

Translation of: C

See Singly-Linked List (element) in Nanoquery.

first = new(link)
//
for (iter = first) (iter != null) (iter = iter.next)
println iter.data
end

NewLISP[edit]

(dolist (x '(a b c d e))
(println x))

Nim[edit]

type Node[T] = ref object
next: Node[T]
data: T
 
proc newNode[T](data: T): Node[T] =
Node[T](data: data)
 
var a = newNode 12
var b = newNode 13
var c = newNode 14
 
proc insertAppend(a, n: var Node) =
n.next = a.next
a.next = n
 
a.insertAppend(b)
b.insertAppend(c)
 
iterator items(a: Node) =
var x = a
while not x.isNil:
yield x
x = x.next
 
for item in a:
echo item.data

Objeck[edit]

 
for(node := head; node <> Nil; node := node->GetNext();) {
node->GetValue()->PrintLine();
};
 

Objective-C[edit]

(See Singly-Linked List (element))

RCListElement *current;
for(current=first_of_the_list; current != nil; current = [current next] )
{
// to get the "datum":
// id dat_obj = [current datum];
}

OCaml[edit]

# let li = ["big"; "fjords"; "vex"; "quick"; "waltz"; "nymph"] in
List.iter print_endline li ;;
big
fjords
vex
quick
waltz
nymph
- : unit = ()

Oforth[edit]

See Singly-Linked List/Element_insertion in Oforth for the full class definition.

Because forEachNext is defined, a linked list responds to all methods defined for Collections : apply, map, filter, ....

: testLink LinkedList new($A, null) dup add($B) dup add($C) ;
testLink apply(#println)
Output:
A
C
B

ooRexx[edit]

See Singly-Linked List/Element Definition in ooRexx for the full class definition.

list=.list~of('A','B','X')
say "Manual list traversal"
index=list~first
loop while index \== .nil
say list~at(index)
index = list~next(index)
end
 
say
say "Do ... Over traversal"
do value over list
say value
end
Output:
Manual list traversal
A
B
X

Do ... Over traversal
A
B
X

Pascal[edit]

See Delphi

Peloton[edit]

This makes a list of the Chinese Public Holiday and lists them first till last and then last till first.

<@ LETCNSLSTLIT>public holidays|開國紀念日^和平紀念日^婦女節、兒童節合併假期^清明節^國慶日^春節^端午節^中秋節^農曆除夕</@>
<@ OMT>From First to Last</@>
<@ ITEFORSZELSTLIT>public holidays|
<@ SAYLST>...</@><@ ACTMOVFWDLST>...</@>
</@>
<@ OMT>From Last to First (pointer is still at end of list)</@>
<@ ITEFORSZELSTLIT>public holidays|
<@ SAYLST>...</@><@ ACTMOVBKWLST>...</@>
</@>

This variable length Simplified Chinese rendition of the same code is

<# 指定构造列表字串>public holidays|開國紀念日^和平紀念日^婦女節、兒童節合併假期^清明節^國慶日^春節^端午節^中秋節^農曆除夕</#>
<# 忽略>From First to Last</#>
<# 迭代迭代次数结构大小列表字串>public holidays|
<# 显示列表>...</#><# 运行移位指针向前列表>...</#>
</#>
<# 忽略>From Last to First (pointer is still at end of list)</#>
<# 迭代迭代次数结构大小列表字串>public holidays|
<# 显示列表>...</#><# 运行移位指针向后列表>...</#>
</#>

Perl[edit]

We use Class::Tiny to get OO functionality with minimal effort.

package SSL_Node;
use strict;
use Class::Tiny qw( val next );
 
sub BUILD {
my $self = shift;
exists($self->{val}) or die "Must supply 'val'";
if (exists $self->{next}) {
ref($self->{next}) eq 'SSL_Node'
or die "If supplied, 'next' must be an SSL_Node";
}
return;
}
 
package main;
use strict;
# Construct an example list,
my @vals = 1 .. 10;
my $countdown = SSL_Node->new(val => shift(@vals));
while (@vals) {
my $head = SSL_Node->new(val => shift(@vals), next => $countdown);
$countdown = $head;
}
# ...then traverse it.
my $node = $countdown;
while ($node) {
print $node->val, "... ";
$node = $node->next;
}
print "\n";
Output:
10... 9... 8... 7... 6... 5... 4... 3... 2... 1...

Phix[edit]

See also Removal.

with javascript_semantics
enum NEXT,DATA
constant empty_sll = {{1}}
sequence sll = deep_copy(empty_sll)
 
procedure insert_after(object data, integer pos=length(sll))
    sll = append(sll,{sll[pos][NEXT],data})
    sll[pos][NEXT] = length(sll)
end procedure
 
insert_after("ONE")
insert_after("TWO")
insert_after("THREE")
 
?sll
 
procedure show()
integer idx = sll[1][NEXT]
    while idx!=1 do
        ?sll[idx][DATA]
        idx = sll[idx][NEXT]
    end while
end procedure
show()
Output:
{{2},{3,"ONE"},{4,"TWO"},{1,"THREE"}}
"ONE"
"TWO"
"THREE"

PicoLisp[edit]

We might use map functions

(mapc println '(a "cde" (X Y Z) 999))

or flow control functions

(for X '(a "cde" (X Y Z) 999)
(println X) )
Output:
for both cases:
a
"cde"
(X Y Z)
999

PL/I[edit]

*process source attributes xref or(!);
/*********************************************************************
* 25.10.2013 Walter Pachl
* 'set dd:in=d:\sll.txt,recsize(80)'
* 'sll'
*********************************************************************/

sll: Proc Options(main);
Dcl in Record Input;
Dcl sysprint Print;
Dcl 1 elem Based(p),
2 next Ptr Init(null()),
2 value Char(20) Var;
Dcl head Ptr;
Dcl p Ptr;
Dcl prev Ptr;
Dcl i Bin Fixed(31);
Dcl rec Char(80) Var;
Dcl null Builtin;
On Endfile(in) goto show;
Do i=1 By 1;
Read File(in) Into(rec);
alloc elem set(p);
If i=1 Then Do;
head=p;
prev=head;
value=rec;
End;
Else Do;
prev->next=p;
prev=p;
value=rec;
End;
End;
 
show:
p=head;
Do i=1 By 1 while(p^=null());
Put Edit(i,p->value)(skip,f(3),x(1),a);
p=p->next;
End;
End;
Output:
  1 Walter
  2 Pachl
  3 wrote
  4 this

PureBasic[edit]

Procedure traverse(*node.MyData)
While *node
;access data, i.e. PrintN(Str(*node\Value))
*node = *node\next
Wend
EndProcedure
 
;called using
traverse(*firstnode.MyData)

Python[edit]

for node in lst:
print node.value

Any Python class can define next() and __iter__() methods so that it can be used with the normal for iteration syntax. In this example the "lst" could be an instance of any Python list, tuple, dictionary, or any sort of object which defines an iterator. It could also be a generator (a type of function which yields results upon each successive invocation). The notion of a "singly linked list" is somewhat more primitive than normal Python built-in objects.

class LinkedList(object):
"""USELESS academic/classroom example of a linked list implemented in Python.
Don't ever consider using something this crude! Use the built-in list() type!
"""

def __init__(self, value, next):
self.value = value;
self.next = next
def __iter__(self):
node = self
while node != None:
yield node.value
node = node.next;
 
lst = LinkedList("big", next=
LinkedList(value="fjords",next=
LinkedList(value="vex", next=
LinkedList(value="quick", next=
LinkedList(value="waltz", next=
LinkedList(value="nymph", next=None))))));
 
for value in lst:
print value,;
print
Output:
big fjords vex quick waltz nymph

Racket[edit]

Since singly-linked lists that are made of cons cells are one of the most common primitive types in Racket, there is a lot of built-in functionality that scans these lists:

 
#lang racket
 
(define l (list 1 2 3))
 
;; scan the list and collect a list of function results
(map add1 l)
 
;; scan the list and run some function on each element for its side-effect
(for-each displayln l)
 
;; scan a list and sum up its elements
(foldl + 0 l)
 
;; same as the above three, using a more modern syntax that is often
;; more convenient
(for/list ([x (in-list l)]) (add1 x))
(for ([x (in-list l)]) (displayln x))
(for/fold ([sum 0]) ([x (in-list l)]) (+ x sum))
 
;; the same as the first, but make up a vector of results
(for/vector ([x (in-list l)]) (add1 x))
 
;; there is less support for mutable pairs, but it's still extensive
;; enough to cover all the basics
(require racket/mpair)
(define ml (mlist 1 2 3))
(mmap add1 ml)
(mfor-each displayln ml)
(for ([x (in-mlist ml)]) (displayln x))
 

Raku[edit]

(formerly Perl 6)

With Pair[edit]

Built-in list processing in Raku is not specifically based on singly-linked lists, but works at a higher abstraction level that encapsulates such implementation choices. Nonetheless, it's trivial to use the Pair type to build what is essentially a Lisp-style cons list, and in fact, the => pair constructor is right associative for precisely that reason. We traverse such a list here using a 3-part loop:

my $list = 1 => 2 => 3 => 4 => 5 => 6 => Mu;
 
loop (my $l = $list; $l; $l.=value) {
say $l.key;
}
Output:
1
2
3
4
5
6

It would be pretty easy to make such lists iterable as normal Raku lists, if anyone really cared to...

Well, shoot, let's just go ahead and do it. We'll pretend the Pair type is really a list type. (And we show how you turn an ordinary list into a cons list using a reduction. Note how the [=>] reduction is also right associative, just like the base operator.)

use MONKEY-TYPING;
augment class Pair {
method traverse () {
gather loop (my $l = self; $l; $l.=value) {
take $l.key;
}
}
}
 
my $list = [=>] 'Ⅰ' .. 'Ⅻ', Mu;
say ~$list.traverse;
Output:
Ⅰ Ⅱ Ⅲ Ⅳ Ⅴ Ⅵ Ⅶ Ⅷ Ⅸ Ⅹ Ⅺ Ⅻ

With custom type[edit]

Extending class Cell from Singly-linked_list/Element_definition#Raku:

    method Seq {
self, *.next ...^ !*
}

Usage:

my $list = (cons 10, (cons 20, (cons 30, Nil)));
 
for $list.Seq -> $cell {
say $cell.value;
}
Output:
10
20
30

Retro[edit]

: traverse ( l- ) repeat @ 0; again ;

Or, using combinators:

last [ drop ] ^types'LIST [email protected]

With combinators you can also perform an operation on each element in a linked list:

last [ @d->name puts space ] ^types'LIST [email protected]

REXX[edit]

/* REXX ********************************************************************
* 25.10.2013 Walter Pachl
*********************************************************************/

in='d:\sll.txt'
Do i=1 By 1 while lines(in)>0
rec=linein(in)
elem.i.val=rec
elem.i.next=0
ip=i-1
elem.ip.next=i
End;
c=1
Do While c<>0
Say c elem.c.val
c=elem.c.next
End

Ruby[edit]

referring to Singly-Linked List (element)#Ruby and Singly-Linked List (element insertion)#Ruby

head = ListNode.new("a", ListNode.new("b", ListNode.new("c")))
head.insertAfter("b", "b+")
 
# then:
head.each {|node| print node.value, ","}
puts
 
# or
current = head
begin
print current.value, ","
end while current = current.succ
puts
Output:
a,b,b+,c,
a,b,b+,c,

Run BASIC[edit]

list$ = "now is the time for all good men"
for lnk = 1 to 8
print lnk;"->";word$(list$,lnk)
next lnk
Output:
1->now
2->is
3->the
4->time
5->for
6->all
7->good
8->men

Rust[edit]

Extending Singly-Linked List (element)#Rust. Please see that page for the Linked List struct declarations.

In Rust, there are three ways to pass something: by value (which forfeits ownership), by reference (there can be infinitely many immutable references to an object), or by mutable reference (there may only be one mutable reference and no other immutable ones).

The following will demonstrate iteration all three ways.

// 
//
// Iteration by value (simply empties the list as the caller now owns all values)
//
//
pub struct IntoIter<T>(List<T>);
 
impl<T> Iterator for IntoIter<T> {
type Item = T;
fn next(&mut self) -> Option<Self::Item> {
self.0.head.take().map(|node| {
let node = *node;
self.0.head = node.next;
node.elem
})
}
}
 
//
//
// Iteration by immutable reference
//
//
 
pub struct Iter<'a, T: 'a> {
next: Option<&'a Node<T>>,
}
 
impl<'a, T> Iterator for Iter<'a, T> {
type Item = &'a T;
fn next(&mut self) -> Option<Self::Item> {
self.next.take().map(|node| {
self.next = node.next.as_ref().map(|node| &**node);
&node.elem
})
}
}
 
//
//
// Iteration by mutable reference
//
//
 
pub struct IterMut<'a, T: 'a> {
next: Option<&'a mut Node<T>>,
}
 
impl<'a, T> Iterator for IterMut<'a, T> {
type Item = &'a mut T;
fn next(&mut self) -> Option<Self::Item> {
self.next.take().map(|node| {
self.next = node.next.as_mut().map(|node| &mut **node);
&mut node.elem
})
}
}
 
//
//
// Methods implemented for List<T>
//
//
 
impl<T> List<T> {
pub fn into_iter(self) -> IntoIter<T> {
IntoIter(self)
}
 
pub fn iter<'a>(&'a self) -> Iter<'a,T> {
Iter { next: self.head.as_ref().map(|node| &**node) }
}
 
pub fn iter_mut(&mut self) -> IterMut<T> {
IterMut { next: self.head.as_mut().map(|node| &mut **node) }
}
 
}

Scala[edit]

You can use pattern matching for traversing a list.

 
/*
Here is a basic list definition
 
sealed trait List[+A]
case class Cons[+A](head: A, tail: List[A]) extends List[A]
case object Nil extends List[Nothing]
*/

 
def traverse[A](as: List[A]): Unit = as match {
case Nil => print("End")
case Cons(h, t) => {
print(h + " ")
traverse(t)
}
}
 

Scheme[edit]

(define (traverse seq func)
(if (null? seq)
'()
(begin
(func (car seq))
(traverse (cdr seq) func))))

Sidef[edit]

var list = 'a':'b':'c':nil;
#var list = ['a', ['b', ['c']]];
#var list = Pair.new('a', Pair.new('b', Pair.new('c', nil)));
 
for (var l = list; l != nil; l = l[1]) {
say l[0];
}
Output:
a
b
c

SSEM[edit]

Linked lists are a comparatively easy data structure to implement in machine language, although the SSEM does not really have enough storage to make them practically useful. A linked list consists of any number of cons cells, i.e. pairs of successive words in storage where the first word holds a data item and the second holds either a pointer to the next pair or else a special nil value—represented here by 0, although any negative address would also work—indicating we have reached the end of the list. The pairs or cons cells can be scattered arbitrarily through the available storage space. This program traverses the list '(1 2 3), and halts with the last value in the accumulator. It makes some use of instruction arithmetic (self-modifying code).

11101000000000100000000000000000   0. -23 to c
10011000000000010000000000000000 1. Sub. 25
10010000000001100000000000000000 2. c to 9
10101000000000010000000000000000 3. Sub. 21
11010000000001100000000000000000 4. c to 11
10010000000000100000000000000000 5. -9 to c
10010000000001100000000000000000 6. c to 9
11010000000000100000000000000000 7. -11 to c
11010000000001100000000000000000 8. c to 11
00000000000000000000000000000000 9. to be generated at run time
00101000000001100000000000000000 10. c to 20
00000000000000000000000000000000 11. to be generated at run time
00000000000000110000000000000000 12. Test
00011000000000000000000000000000 13. 24 to CI
10011000000001100000000000000000 14. c to 25
10011000000000100000000000000000 15. -25 to c
10011000000001100000000000000000 16. c to 25
01101000000000000000000000000000 17. 22 to CI
00101000000000100000000000000000 18. -20 to c
00000000000001110000000000000000 19. Stop
00000000000000000000000000000000 20. variable: negation of car
10000000000000000000000000000000 21. constant 1
11111111111111111111111111111111 22. constant -1
00000000000000100000000000000000 23. -0 to c
10001000000000000000000000000000 24. constant 17 (jump target)
00111000000000000000000000000000 25. 28 (pointer variable)
01000000000000000000000000000000 26. 2
01111000000000000000000000000000 27. pointer: 30
10000000000000000000000000000000 28. 1
01011000000000000000000000000000 29. pointer: 26
11000000000000000000000000000000 30. 3
00000000000000000000000000000000 31. 0 (nil)

SSEM programs can be difficult to take in: the constant negations, subtractions, and indirect jumps often obscure the underlying algorithm. To clarify what is going on, here is a pseudocode version of the same program:

start:    load         loadZero
          add          pointer
          store        loadCar
          add          #1
          store        loadCdr
loadCar:  ; generated at run time
          store        value
loadCdr:  ; generated at run time
          branchOnZero end
          store        pointer
          jump         start
end:      load         value
          halt
value:            0 ; variable
loadZero: load         #0
pointer:          28

26 and 27:        (2 . 30)
28 and 29:        (1 . 26)
30 and 31:        (3 . 0)

Stata[edit]

See Singly-linked list/Element definition#Stata.

Tcl[edit]

Using the class definition from Singly-Linked List (element) (and bearing in mind the general notes on lists given there) we'll modify that class so that lists have an iteration method...

Works with: Tcl version 8.6
oo::define List {
method for {varName script} {
upvar 1 $varName var
set elem [self]
while {$elem ne ""} {
set var [$elem value]
uplevel 1 $script
set elem [$elem next]
}
}
}

Now, a demonstration...

set list {}
foreach n {1 3 5 7 2 4 6 8} {
set list [List new $n $list]
}
$list for x {
puts "we have a $x in the list"
}

Trith[edit]

[1 2 3 4 5] [print] each

Visual Basic .NET[edit]

Private Sub Iterate(ByVal list As LinkedList(Of Integer))
Dim node = list.First
Do Until node Is Nothing
node = node.Next
Loop
End Sub

Wart[edit]

each x '(1 2 3)
prn x

Wren[edit]

Library: Wren-llist
Library: Wren-fmt
import "/llist" for LinkedList
import "/fmt" for Fmt
 
//create a new linked list and add the first 50 positive integers to it
var ll = LinkedList.new(1..50)
 
// traverse the linked list
for (i in ll) {
Fmt.write("$4d ", i)
if (i % 10 == 0) System.print()
}
Output:
   1    2    3    4    5    6    7    8    9   10 
  11   12   13   14   15   16   17   18   19   20 
  21   22   23   24   25   26   27   28   29   30 
  31   32   33   34   35   36   37   38   39   40 
  41   42   43   44   45   46   47   48   49   50 

XPL0[edit]

def \Node\ Link, Data;          \linked list element definition
int Node, List;
[Node:= List; \traverse the linked list
while Node # 0 do
Node:= Node(Link); \move to next node
]

Yabasic[edit]

// Rosetta Code problem: http://rosettacode.org/wiki/Singly-linked_list/Element_insertion & removal & traverse
// by Galileo, 02/2022
 
FIL = 1 : DATO = 2 : LINK = 3
countNodes = 0 : Nodes = 10
 
dim list(Nodes, 3)
 
 
sub searchNode(node)
local i, prevNode
 
for i = 1 to countNodes
if i = node break
prevNode = list(prevNode, LINK)
next
 
return prevNode
end sub
 
sub insertNode(node, newNode, after)
local prevNode, i
 
prevNode = searchNode(node)
 
if after prevNode = list(prevNode, LINK)
 
for i = 1 to Nodes
if not list(i, FIL) break
next
 
list(i, FIL) = true
list(i, DATO) = newNode
list(i, LINK) = list(prevNode, LINK)
list(prevNode, LINK) = i
 
countNodes = countNodes + 1
if countNodes = Nodes then Nodes = Nodes + 10 : redim list(Nodes, 3) : end if
end sub
 
 
sub removeNode(n)
local prevNode, node
 
prevNode = searchNode(n)
node = list(prevNode, LINK)
list(prevNode, LINK) = list(node, LINK)
list(node, FIL) = false
countNodes = countNodes - 1
end sub
 
 
sub printNode(node)
local prevNode
 
prevNode = searchNode(node)
node = list(prevNode, LINK)
print list(node, DATO);
print
end sub
 
 
sub traverseList()
local i
 
for i = 1 to countNodes
printNode(i)
next
end sub
 
 
insertNode(1, 1000, true)
insertNode(1, 2000, true)
insertNode(1, 3000, true)
 
traverseList()
 
removeNode(2)
 
print
traverseList()
 
Output:
1000
3000
2000

1000
2000
---Program done, press RETURN---

Zig[edit]

Using the LinkedList struct definition from Singly-Linked List (element)

const std = @import("std");
 
pub fn main() anyerror!void {
var l1 = LinkedList(i32).init();
 
try l1.add(1);
try l1.add(2);
try l1.add(4);
try l1.add(3);
 
var h = l1.head;
 
while (h) |head| : (h = head.next) {
std.log.info("> {}", .{ head.value });
}
}
Output:
info: > 1
info: > 2
info: > 4
info: > 3

zkl[edit]

foreach n in (List(1,2,3) {...}
List(1,2,3).pump(...) // traverse and munge elements, generalized apply/map
List(1,2,3).filter(...)
List(1,2,3).filter22(...) // partition list
List(1,2,3).reduce(...)
List(1,2,3).apply(...)
List(1,2,3).sum()
List(1,2,3).run() // treat each element as f, perform f()
List(1,2,3).enumerate()
List(1,2,3).reverse()
List(1,2,3).concat()
List(1,2,3).shuffle()