# Apply a callback to an array

Apply a callback to an array
You are encouraged to solve this task according to the task description, using any language you may know.

In this task, the goal is to take a combined set of elements and apply a function to each element.

## ACL2

 This example is incorrect. This is recursive list processing with a hard-coded function. First class functions are not required in this problem; "second class" functions will do (see C solution, etc). Please fix the code and remove this message.

ACL2 does not have first-class functions; this is close, however:

(defun sq-each (xs)   (if (endp xs)       nil       (cons (* (first xs) (first xs))             (sq-each (rest xs)))))

## ActionScript

package{    public class ArrayCallback    {        public function main():void        {            var nums:Array = new Array(1, 2, 3);            nums.map(function(n:Number, index:int, arr:Array):void { trace(n * n * n); });             // You can also pass a function reference            nums.map(cube);        }         private function cube(n:Number, index:int, arr:Array):void        {            trace(n * n * n);        }    }}

Works with: GNAT version GPL 2005
with Ada.Text_Io; with Ada.Integer_text_IO;  procedure Call_Back_Example is    -- Purpose: Apply a callback to an array    -- Output: Prints the squares of an integer array to the console     -- Define the callback procedure    procedure Display(Location : Positive; Value : Integer) is    begin       Ada.Text_Io.Put("array(");       Ada.Integer_Text_Io.Put(Item => Location, Width => 1);       Ada.Text_Io.Put(") = ");       Ada.Integer_Text_Io.Put(Item => Value * Value, Width => 1);       Ada.Text_Io.New_Line;    end Display;     -- Define an access type matching the signature of the callback procedure    type Call_Back_Access is access procedure(L : Positive; V : Integer);     -- Define an unconstrained array type    type Value_Array is array(Positive range <>) of Integer;     -- Define the procedure performing the callback    procedure Map(Values : Value_Array; Worker : Call_Back_Access) is    begin       for I in Values'range loop          Worker(I, Values(I));       end loop;    end Map;     -- Define and initialize the actual array    Sample : Value_Array := (5,4,3,2,1);  begin    Map(Sample, Display'access);    end Call_Back_Example;

## Aime

voidmap(list l, void (*fp) (object)){    integer i;     i = 0;    while (i < l_length(l)) {	fp(l[i]);	i += 1;    }}  voidout(object o){    o_integer(o);    o_byte(10);}  integermain(void){    list l;     l_append(l, 0);    l_append(l, 1);    l_append(l, 2);    l_append(l, 3);     map(l, out);     return 0;}

## ALGOL 68

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
 PROC call back proc = (INT location, INT value)VOID: (   printf(($"array["g"] = "gl$, location, value)) );  PROC map = (REF[]INT array, PROC (INT,INT)VOID call back)VOID: (   FOR i FROM LWB array TO UPB array DO      call back(i, array[i])   OD );  main: (   [4]INT array := ( 1, 4, 9, 16 );   map(array, call back proc) )

Output:

array[         +1] =          +1
array[         +2] =          +4
array[         +3] =          +9
array[         +4] =         +16


## AppleScript

on callback for arg	-- Returns a string like "arc has 3 letters"	arg & " has " & (count arg) & " letters"end callback set alist to {"arc", "be", "circle"}repeat with aref in alist	-- Passes a reference to some item in alist	-- to callback, then speaks the return value.	say (callback for aref)end repeat

If the callback would set arg's contents to "something", then alist would be mutated.

## AutoHotkey

map("callback", "3,4,5") callback(array){  Loop, Parse, array, ,    MsgBox % (2 * A_LoopField)} map(callback, array){  %callback%(array)}

## AWK

$awk 'func psqr(x){print x,x*x}BEGIN{split("1 2 3 4 5",a);for(i in a)psqr(a[i])}'4 165 251 12 43 9 ## Babel We can alter the list in place: ((main { (1 1 2 3 5 8 13 21) dup {double !} each {%d ' ' . <<} each}) (double { dup 2 * set })) Or, we can leave the original list unmodified: ((main { (1 1 2 3 5 8 13 21) {double !} each collect ! {%d ' ' . <<} each}) (double { 2 * }) (collect { -1 take })) Both versions produce the same output: 2 2 4 6 10 16 26 42  Because lists and arrays are distinct in Babel, we can also do a similar procedure over an array, with the same results as above: ((main { [val 1 1 2 3 5 8 13 21] {double !} eachar collect ! {%d ' ' . <<} each}) (double { 2 * }) (collect { -1 take })) ## BBC BASIC  DIM a(4) a() = 1, 2, 3, 4, 5 PROCmap(a(), FNsqrt()) FOR i = 0 TO 4 PRINT a(i) NEXT END DEF FNsqrt(n) = SQR(n) DEF PROCmap(array(), RETURN func%) LOCAL I% FOR I% = 0 TO DIM(array(),1) array(I%) = FN(^func%)(array(I%)) NEXT ENDPROC  Produces this output:  1 1.41421356 1.73205081 2 2.23606798  ## Bracmat ( ( callbackFunction1 = location value . !arg:(?location,?value) & out$(str$(array[ !location "] = " !!value)) )& ( callbackFunction2 = location value . !arg:(?location,?value) & !!value^2:?!value )& ( map = arr len callback i . !arg:(?arr,?len,?callback) & 0:?i & whl ' ( !i:<!len & !callback$(!i,!i$!arr) & 1+!i:?i ) )& tbl$(array,4)& 1:?(0$array)& 2:?(1$array)& 3:?(2$array)& 4:?(3$array)& map$(array,4,callbackFunction1)& map$(array,4,callbackFunction2)& map$(array,4,callbackFunction1)); Output: array[0] = 1 array[1] = 2 array[2] = 3 array[3] = 4 array[0] = 1 array[1] = 4 array[2] = 9 array[3] = 16 ## Brat #Print out each element in array[:a :b :c :d :e].each { element | p element} Alternatively: [:a :b :c :d :e].each ->p ## C callback.h #ifndef CALLBACK_H#define CALLBACK_H /* * By declaring the function in a separate file, we allow * it to be used by other source files. * * It also stops ICC from complaining. * * If you don't want to use it outside of callback.c, this * file can be removed, provided the static keyword is prepended * to the definition. */void map(int* array, int len, void(*callback)(int,int)); #endif callback.c #include <stdio.h>#include "callback.h" /* * We don't need this function outside of this file, so * we declare it static. */static void callbackFunction(int location, int value){ printf("array[%d] = %d\n", location, value);} void map(int* array, int len, void(*callback)(int,int)){ int i; for(i = 0; i < len; i++) { callback(i, array[i]); }} int main(){ int array[] = { 1, 2, 3, 4 }; map(array, 4, callbackFunction); return 0;} Output  array[0] = 1 array[1] = 2 array[2] = 3 array[3] = 4  ## C# Works with: C# version 2.0+ Works with: Visual C# version 2005 using System; static class Program{ // Purpose: Apply a callback (or anonymous method) to an Array // Output: Prints the squares of an int array to the console. // Compiler: Visual Studio 2005 // Framework: .net 2 [STAThread] public static void Main() { int[] intArray = { 1, 2, 3, 4, 5 }; // Using a callback, Console.WriteLine("Printing squares using a callback:"); Array.ForEach<int>(intArray, PrintSquare); // or using an anonymous method: Console.WriteLine("Printing squares using an anonymous method:"); Array.ForEach<int> ( intArray, delegate(int value) { Console.WriteLine(value * value); }); } public static void PrintSquare(int value) { Console.WriteLine(value * value); }} Works with: C# version 3.0+ This version uses the C# 3 lambda notation. int[] intArray = { 1, 2, 3, 4, 5 };Array.ForEach(intArray, i => Console.WriteLine(i * i)); ## C++ Works with: g++ version 4.1.1 ### C-Style Array #include <iostream> //cout for printing#include <algorithm> //for_each defined here //create the function (print the square)void print_square(int i) { std::cout << i*i << " ";} int main() { //create the array int ary[]={1,2,3,4,5}; //stl for_each std::for_each(ary,ary+5,print_square); return 0;}//prints 1 4 9 16 25 ### std::vector Library: STL #include <iostream> // cout for printing#include <algorithm> // for_each defined here#include <vector> // stl vector class // create the function (print the square)void print_square(int i) { std::cout << i*i << " ";} int main() { // create the array std::vector<int> ary; ary.push_back(1); ary.push_back(2); ary.push_back(3); ary.push_back(4); ary.push_back(5); // stl for_each std::for_each(ary.begin(),ary.end(),print_square); return 0;}//prints 1 4 9 16 25 More tricky with binary function #include <iostream> // cout for printing#include <algorithm> // for_each defined here#include <vector> // stl vector class#include <functional> // bind and ptr_fun // create a binary function (print any two arguments together)template<class type1,class type2>void print_juxtaposed(type1 x, type2 y) { std::cout << x << y;} int main() { // create the array std::vector<int> ary; ary.push_back(1); ary.push_back(2); ary.push_back(3); ary.push_back(4); ary.push_back(5); // stl for_each, using binder and adaptable unary function std::for_each(ary.begin(),ary.end(),std::bind2nd(std::ptr_fun(print_juxtaposed<int,std::string>),"x ")); return 0;}//prints 1x 2x 3x 4x 5x ### Boost.Lambda Library: Boost using namespace std;using namespace boost::lambda;vector<int> ary(10);int i = 0;for_each(ary.begin(), ary.end(), _1 = ++var(i)); // init arraytransform(ary.begin(), ary.end(), ostream_iterator<int>(cout, " "), _1 * _1); // square and output ### C++11 #include <vector>#include <iostream>#include <algorithm>#include <iterator> int main() { std::vector<int> intVec(10); std::iota(std::begin(intVec), std::end(intVec), 1 ); // Fill the vector std::transform(std::begin(intVec) , std::end(intVec), std::begin(intVec), [](int i) { return i * i ; } ); // Transform it with closures std::copy(std::begin(intVec), end(intVec) , std::ostream_iterator<int>(std::cout, " ")); std::cout << std::endl; return 0;} ## Clean Define a function and an initial (unboxed) array. square x = x * x values :: {#Int}values = {x \\ x <- [1 .. 10]} One can easily define a map for arrays, which is overloaded and works for all kinds of arrays (lazy, strict, unboxed). mapArray f array = {f x \\ x <-: array} Apply the function to the initial array (using a comprehension) and print result. Start :: {#Int}Start = mapArray square values ## Clojure ;; apply a named function, inc(map inc [1 2 3 4]) ;; apply a function(map (fn [x] (* x x)) [1 2 3 4]) ;; shortcut syntax for a function(map #(* % %) [1 2 3 4]) ## COBOL Basic implementation of a map function:  IDENTIFICATION DIVISION. PROGRAM-ID. Map. DATA DIVISION. WORKING-STORAGE SECTION. 01 Table-Size CONSTANT 30. LOCAL-STORAGE SECTION. 01 I USAGE UNSIGNED-INT. LINKAGE SECTION. 01 Table-Param. 03 Table-Values USAGE COMP-2 OCCURS Table-Size TIMES. 01 Func-Id PIC X(30). PROCEDURE DIVISION USING Table-Param Func-Id. PERFORM VARYING I FROM 1 BY 1 UNTIL Table-Size < I CALL Func-Id USING BY REFERENCE Table-Values (I) END-PERFORM GOBACK . ## CoffeeScript  map = (arr, f) -> (f(e) for e in arr)arr = [1, 2, 3, 4, 5]f = (x) -> x * xconsole.log map arr, f # prints [1, 4, 9, 16, 25]  ## Common Lisp Imperative: print 1, 2, 3, 4 and 5: (map nil #'print #(1 2 3 4 5)) Functional: collect squares into new vector that is returned: (defun square (x) (* x x))(map 'vector #'square #(1 2 3 4 5)) Destructive, like the Javascript example; add 1 to every slot of vector *a*: (defvar *a* (vector 1 2 3))(map-into *a* #'1+ *a*) ## Component Pascal BlackBox Component Builder  MODULE Callback;IMPORT StdLog; TYPE Callback = PROCEDURE (x: INTEGER;OUT doubled: INTEGER); Callback2 = PROCEDURE (x: INTEGER): INTEGER; PROCEDURE Apply(proc: Callback; VAR x: ARRAY OF INTEGER); VAR i: INTEGER; BEGIN FOR i := 0 TO LEN(x) - 1 DO; proc(x[i],x[i]); END END Apply; PROCEDURE Apply2(func: Callback2; VAR x: ARRAY OF INTEGER); VAR i: INTEGER; BEGIN FOR i := 0 TO LEN(x) - 1 DO; x[i] := func(x[i]); END END Apply2; PROCEDURE Double(x: INTEGER; OUT y: INTEGER); BEGIN y := x * x; END Double; PROCEDURE Double2(x: INTEGER): INTEGER; BEGIN RETURN x * x END Double2; PROCEDURE Do*; VAR i: INTEGER; ary: ARRAY 10 OF INTEGER; BEGIN FOR i := 0 TO LEN(ary) - 1 DO ary[i] := i END; Apply(Double,ary); FOR i := 0 TO LEN(ary) - 1 DO StdLog.Int(ary[i]);StdLog.Ln END; StdLog.Ln; Apply2(Double2,ary); FOR i := 0 TO LEN(ary) - 1 DO StdLog.Int(ary[i]);StdLog.Ln END END Do;END Callback.  Execute: ^Q Callback.Do Output:  0 1 4 9 16 25 36 49 64 81 0 1 16 81 256 625 1296 2401 4096 6561  ## D import std.stdio, std.algorithm; void main() { auto items = [1, 2, 3, 4, 5]; auto m = items.map!(x => x + 5)(); writeln(m);} Output: [6, 7, 8, 9, 10] ## Delphi  // Declare the callback functionprocedure callback(const AInt:Integer);begin WriteLn(AInt);end; const // Declare a static array myArray:Array[0..4] of Integer=(1,4,6,8,7);var // Declare interator variable i:Integer;begin // Iterate the array and apply callback for i:=0 to length(myArray)-1 do callback(myArray[i]);end.  ## Déjà Vu There is a map builtin that does just this. !. map @++ [ 1 4 8 ] #implemented roughly like this:#map f lst:# ]# for i in lst:# f i# [ Output: [ 2 5 9 ] ## E def array := [1,2,3,4,5]def square(value) { return value * value} Example of builtin iteration: def callback(index, value) { println(Item$index is $value.)}array.iterate(callback) There is no built-in map function yet. The following is one of the ways one could be implemented, returning a plain list (which is usually an array in implementation). def map(func, collection) { def output := [].diverge() for item in collection { output.push(func(item)) } return output.snapshot()}println(map(square, array)) ## Efene square = fn (N) { N * N} # list comprehensionsquares1 = fn (Numbers) { [square(N) for N in Numbers]} # functional formsquares2a = fn (Numbers) { lists.map(fn square:1, Numbers)} # functional form with lambdasquares2b = fn (Numbers) { lists.map(fn (N) { N * N }, Numbers)} # no need for a functionsquares3 = fn (Numbers) { [N * N for N in Numbers]} @publicrun = fn () { Numbers = [1, 3, 5, 7] io.format("squares1 : ~p~n", [squares1(Numbers)]) io.format("squares2a: ~p~n", [squares2a(Numbers)]) io.format("squares2b: ~p~n", [squares2b(Numbers)]) io.format("squares3 : ~p~n", [squares3(Numbers)])}  ## EGL delegate callback( i int ) returns( int ) end program ApplyCallbackToArray function main() values int[] = [ 1, 2, 3, 4, 5 ]; func callback = square; for ( i int to values.getSize() ) values[ i ] = func( values[ i ] ); end for ( i int to values.getSize() ) SysLib.writeStdout( values[ i ] ); end end function square( i int ) returns( int ) return( i * i ); endend ## Elena #define system. #symbol PrintSecondPower = (:n) [ console writeLine:(n * n) ]. #symbol program =[ #var anArray := (1, 2, 3, 4, 5, 6, 7, 8, 9, 10). control foreach:anArray &do:PrintSecondPower.]. ## Erlang A list would be more commonly used in Erlang rather than an array.  1> L = [1,2,3].[1,2,3]  You can use lists:foreach/2 if you just want to apply the callback to each element of the list.  2> lists:foreach(fun(X) -> io:format("~w ",[X]) end, L).1 2 3 ok  Or you can use lists:map/2 if you want to create a new list with the result of the callback on each element.  3> lists:map(fun(X) -> X + 1 end, L).[2,3,4]  Or you can use lists:foldl/3 if you want to accumulate the result of the callback on each element into one value.  4> lists:foldl(fun(X, Sum) -> X + Sum end, 0, L).6  ## Euphoria function apply_to_all(sequence s, integer f) -- apply a function to all elements of a sequence sequence result result = {} for i = 1 to length(s) do -- we can call add1() here although it comes later in the program result = append(result, call_func(f, {s[i]})) end for return resultend function function add1(atom x) return x + 1end function -- add1() is visible here, so we can ask for its routine id? apply_to_all({1, 2, 3}, routine_id("add1"))-- displays {2,3,4} This is also "Example 2" in the Euphoria documentation for routine_id(). Note that this example will not work for multi-dimensional sequences. ## Factor Print each element squared: { 1 2 3 4 } [ sq . ] each Collect return values: { 1 2 3 4 } [ sq ] map ## Fantom In Fantom, functions can be passed to a collection iterator, such as 'each'. 'map' is used similarly, and the results are collected into a list.  class Main{ public static Void main () { [1,2,3,4,5].each |Int i| { echo (i) } Int[] result := [1,2,3,4,5].map |Int i->Int| { return i * i } echo (result) }}  Output: 1 2 3 4 5 [1, 4, 9, 16, 25]  ## FBSL User-defined mapping function: #APPTYPE CONSOLE FOREACH DIM e IN MyMap(Add42, {1, 2, 3}) PRINT e, " ";NEXT PAUSE FUNCTION MyMap(f, a) DIM ret[] FOREACH DIM e IN a ret[] = f(e) NEXT RETURN retEND FUNCTION FUNCTION Add42(n): RETURN n + 42: END FUNCTION Output: 43 44 45 Press any key to continue... Standard MAP() function: #APPTYPE CONSOLE DIM languages[] = {{"English", {"one", "two", "three", "four", "five", "six", "seven", "eight", "nine", "ten"}}, _ {"French", {"un", "deux", "trois", "quatre", "cinq", "six", "sept", "huit", "neuf", "dix"}}} MAP(SpeakALanguage, languages) PAUSE SUB NameANumber(lang, nb, number) PRINT "The number ", nb, " is called ", STRENC(number), " in ", langEND SUB SUB SpeakALanguage(lang) MAP(NameANumber, lang[0], 1 TO 10, lang[1]) PRINT LPAD("", 40, "-")END SUB Output: The number 1 is called "one" in English The number 2 is called "two" in English The number 3 is called "three" in English The number 4 is called "four" in English The number 5 is called "five" in English The number 6 is called "six" in English The number 7 is called "seven" in English The number 8 is called "eight" in English The number 9 is called "nine" in English The number 10 is called "ten" in English ---------------------------------------- The number 1 is called "un" in French The number 2 is called "deux" in French The number 3 is called "trois" in French The number 4 is called "quatre" in French The number 5 is called "cinq" in French The number 6 is called "six" in French The number 7 is called "sept" in French The number 8 is called "huit" in French The number 9 is called "neuf" in French The number 10 is called "dix" in French ---------------------------------------- Press any key to continue... ## Forth This is a word that will call a given function on each cell in an array. : map ( addr n fn -- ) -rot cells bounds do i @ over execute i ! cell +loop ; Example usage: create data 1 , 2 , 3 , 4 , 5 ,data 5 ' 1+ map \ adds one to each element of data ## Fortran Elemental functions. Works with: Fortran version ISO 95 and later module arrCallbackcontains elemental function cube( x ) implicit none real :: cube real, intent(in) :: x cube = x * x * x end function cubeend module arrCallback program testAC use arrCallback implicit none integer :: i, j real, dimension(3,4) :: b, & a = reshape( (/ ((10 * i + j, i = 1, 3), j = 1, 4) /), (/ 3,4 /) ) do i = 1, 3 write(*,*) a(i,:) end do b = cube( a ) ! Applies CUBE to every member of a, ! and stores each result in the equivalent element of b do i = 1, 3 write(*,*) b(i,:) end doend program testAC Works with: ANSI FORTRAN version 77 (with MIL-STD-1753 structured DO) and later  program testCC-- Declare array: integer a(5)CC-- Fill it with Data data a /45,22,67,87,98/CC-- Do something with all elements (in this case: print their squares) do i=1,5 print *,a(i)*a(i) end doC end ## FP {square * . [id, id]}& square: <1,2,3,4,5> ## Frink  f = {|x| x^2} // Anonymous function to square inputa = [1,2,3,5,7]println[map[f, a]]  ## F# Apply a named function to each member of the array. The result is a new array of the same size as the input. let evenp x = x % 2 = 0let result = Array.map evenp [| 1; 2; 3; 4; 5; 6 |] The same can be done using anonymous functions, this time squaring the members of the input array. let result = Array.map (fun x -> x * x) [|1; 2; 3; 4; 5|] Use iter if the applied function does not return a value. Array.iter (fun x -> printfn "%d" x) [|1; 2; 3; 4; 5|] ## FunL [1, 2, 3].foreach( println ) [1, 2, 3].foreach( a -> println(2a) ) Output: 1 2 3 2 4 6  ## GAP a := [1 .. 4];b := ShallowCopy(a); # Apply and replace valuesApply(a, n -> n*n);a;# [ 1, 4, 9, 16 ] # Apply and don't change valuesList(b, n -> n*n);# [ 1, 4, 9, 16 ] # Apply and don't return anything (only side effects)Perform(b, Display);1234 b;# [ 1 .. 4 ] ## Go Translation of: Ruby The task was originally written with a Ruby example, so here are Go versions of the current Ruby examples. Perhaps in contrast to Ruby, it is idiomatic in Go to use the for statement: package main import "fmt" func main() { for _, i := range []int{1, 2, 3, 4, 5} { fmt.Println(i * i) }} Alternatively though, an array-like type can be defined and callback-style methods can be defined on it to apply a function to the elements. package main import "fmt" type intSlice []int func (s intSlice) each(f func(int)) { for _, i := range s { f(i) }} func (s intSlice) Map(f func(int) int) intSlice { r := make(intSlice, len(s)) for j, i := range s { r[j] = f(i) } return r} func main() { s := intSlice{1, 2, 3, 4, 5} s.each(func(i int) { fmt.Println(i * i) }) fmt.Println(s.Map(func(i int) int { return i * i }))} Output: 1 4 9 16 25 [1 4 9 16 25]  ## Groovy Print each value in a list [1,2,3,4].each { println it } Create a new list containing the squares of another list [1,2,3,4].collect { it * it } ## Haskell ### List Works with: GHC let square x = x*xlet values = [1..10]map square values Using list comprehension to generate a list of the squared values [square x | x <- values] Using function composition to create a function that will print the squares of a list let printSquares = mapM_ (print.square)printSquares values ### Array Works with: GHC import Data.Array.IArraylet square x = x*xlet values = array (1,10) [(i,i)|i <- [1..10]] :: Array Int Intamap square values ## Icon and Unicon procedure main() local lst lst := [10, 20, 30, 40] every callback(write,!lst)end procedure callback(p,arg) return p(" -> ", arg)end ## IDL Hard to come up with an example that isn't completely contrived. IDL doesn't really distinguish between a scalar and an array; thus b = a^3 will yield a scalar if a is scalar or a vector if a is a vector or an n-dimensional array if a is an n-dimensional array ## Io list(1,2,3,4,5) map(squared) ## J Solution:  "_1 Example:  callback =: *: array =: 1 2 3 4 5 callback"_1 array1 4 9 16 25 But note that this is a trivial example since *: 1 2 3 4 5 would get the same result. Then again, this is something of a trivial exercise in J since all of J is designed around the idea of applying functions usefully to arrays. ## Java As of the current version of Java, you have to define an interface for each type of function you want to use. The next version of Java will introduce function types. So if you want to perform an action (which doesn't return anything) on an array of int's: interface IntToVoid { void run(int x);} for (int z : myIntArray) { new IntToVoid() { public void run(int x) { System.out.println(x); } }.run(z);} Or if you want to perform "map" - return an array of the results of function applications: interface IntToInt { int run(int x);} int[] result = new int[myIntArray.length];for (int i = 0; i < myIntArray.length; i++) { result[i] = new IntToInt() { public int run(int x) { return x * x; } }.run(myIntArray[i]);} ## JavaScript ### ES3 function map(a, func) { var ret = []; for (var i = 0; i < a.length; i++) { ret[i] = func(a[i]); } return ret;} map([1, 2, 3, 4, 5], function(v) { return v * v; }); ### ES5 [1, 2, 3, 4, 5].map(function(v) { return v * v; }); ### ES6 [1, 2, 3, 4, 5].map(v => v * v); The result is always: [1, 4, 9, 16, 25] ## Joy [1 2 3 4 5] [dup *] map. ## jq # Illustration of map/1 using the builtin filter: expmap(exp) # exponentiate each item in the input list # A compound expression can be specified as the argument to map, e.g.map( (. * .) + sqrt ) # x*x + sqrt(x) # The compound expression can also be a composition of filters, e.g.map( sqrt|floor ) # the floor of the sqrt # Array comprehensionreduce .[] as$n ([]; . + [ exp ]) # Elementwise operation  [.[] + 1 ]   # add 1 to each element of the input array 
Here is a transcript illustrating how the last of these jq expressions can be evaluated:
$jq -c ' [.[] + 1 ]'[0, 1 , 10][1,2,11] ## Julia  numbers = [1, 3, 5, 7] square1 = [square(n) for n in numbers] # list comprehension squares2a = map(square, numbers) # functional form squares2b = map(x -> x*x, numbers) # functional form with lambda #There is also extended block form for the map function squares2c = map(numbers) do x sum = 0 for i = 1:x sum += x^2 #trivial, but you get the point end return sumend squares3 = [n * n for n in numbers] # no need for a function, squares4 = numbers .* numbers # element-wise operation squares4a = numbers .^ 2 # most arithmetic operations can be done element-wise ## Lang5 : square(*) dup * ;[1 2 3 4 5] square . "\n" .[1 2 3 4 5] 'square apply . "\n" . ## Lasso define cube(n::integer) => #n*#n*#n local( mynumbers = array(1, 2, 3, 4, 5), mycube = array) #mynumbers -> foreach => { #mycube -> insert(cube(#1))} #mycube -> array(1, 8, 27, 64, 125) ## Lisaac + a : ARRAY(INTEGER);+ b : {INTEGER;}; a := ARRAY(INTEGER).create 1 to 3;1.to 3 do { i : INTEGER; a.put i to i;}; b := { arg : INTEGER; (arg * arg).print; '\n'.print;}; a.foreach b; ## Logo to square :x output :x * :xendshow map "square [1 2 3 4 5] ; [1 4 9 16 25]show map [? * ?] [1 2 3 4 5] ; [1 4 9 16 25]foreach [1 2 3 4 5] [print square ?] ; 1 4 9 16 25, one per line ## Lua Say we have an array: myArray = {1, 2, 3, 4, 5} A map function for this would be map = function(f, data) local result = {} for k,v in ipairs(data) do result[k] = f(v) end return resultend Together with our array and a square function this yields: myFunc = function(x) return x*x end print(unpack( map(myFunc, myArray) ))--> 1 4 9 16 25 If you used pairs() instead of ipairs(), this would even work on a hash table in general. However, remember that hash table do not have an implicit ordering on their elements, like arrays do, so pairs() is not guaranteed to return the elements in the same order as ipairs() ## M4 define(foreach', pushdef($1')_foreach($@)popdef($1')')dnldefine(_arg1', $1')dnldefine(_foreach', ifelse($2', ()', ',   define($1', _arg1$2)$3'$0($1', (shift$2), $3')')')dnldnldefine(apply',foreach(x',$1,$2(x)')')dnldnldefine(z',eval($1*2') ')dnlapply((1,2,3)',z')

Output:

2 4 6


## Maple

For lists and sets, which in Maple are immutable, a new object is returned. Either the built-in procedure map, or the short syntax of a trailing tilde (~) on the applied operator may be used.

 > map( sqrt, [ 1.1, 3.2, 5.7 ] );                [1.048808848, 1.788854382, 2.387467277] > map( x -> x + 1, { 1, 3, 5 } );                               {2, 4, 6} > sqrt~( [ 1.1, 3.2, 5.7 ] );                [1.048808848, 1.788854382, 2.387467277] > (x -> x + 1)~( { 1, 3, 5 } );                               {2, 4, 6}

For Arrays (Vectors, Matrices, etc.) both map and trailing tilde also work, and by default create a new object, leaving the input Array unchanged.

 > a := Array( [ 1.1, 3.2, 5.7 ] );                          a := [1.1, 3.2, 5.7] > sqrt~( a );                [1.048808848, 1.788854382, 2.387467277] > a;                            [1.1, 3.2, 5.7] > map( sqrt, a );                [1.048808848, 1.788854382, 2.387467277] > a;                            [1.1, 3.2, 5.7]

However, since these are mutable data structures in Maple, it is possible to use map to modify its input according to the applied procedure.

 > map[inplace]( sqrt, a );                [1.048808848, 1.788854382, 2.387467277] > a;                [1.048808848, 1.788854382, 2.387467277]

The Array a has been modified.

It is also possible to pass additional arguments to the mapped procedure.

 > map( +, [ 1, 2, 3 ], 3 );                               [4, 5, 6]

Passing additional arguments *before* the arguments from the mapped data structure is achieved using map2, or the more general map[n] procedure.

 > map2( -, 5, [ 1, 2, 3 ] );                               [4, 3, 2] > map[2]( /, 5, [ 1, 2, 3 ] );                             [5, 5/2, 5/3]

## Mathematica

(#*#)& /@ {1, 2, 3, 4} Map[Function[#*#], {1, 2, 3, 4}] Map[((#*#)&,{1,2,3,4}] Map[Function[w,w*w],{1,2,3,4}]

## MATLAB

There are two types of arrays in MATLAB: arrays and cell arrays. MATLAB includes two functions, one for each of these data types, that accomplish the specification for this task. For arrays, we use "arrayfun()"; for cell arrays we use "cellfun()".
Example: For both of these function the first argument is a function handle for the function we would like to apply to each element. The second argument is the array whose elements are modified by the function. The function can be any function, including user defined functions.

>> array = [1 2 3 4 5] array =      1     2     3     4     5 >> arrayfun(@sin,array) ans =   Columns 1 through 4    0.841470984807897   0.909297426825682   0.141120008059867  -0.756802495307928   Column 5   -0.958924274663138 >> cellarray = {1,2,3,4,5} cellarray =      [1]    [2]    [3]    [4]    [5] >> cellfun(@tan,cellarray) ans =   Columns 1 through 4    1.557407724654902  -2.185039863261519  -0.142546543074278   1.157821282349578   Column 5   -3.380515006246586

## Maxima

/* for lists or sets */ map(sin, [1, 2, 3, 4]);map(sin, {1, 2, 3, 4}); /* for matrices */ matrixmap(sin, matrix([1, 2], [2, 4]));

## Modula-3

MODULE Callback EXPORTS Main; IMPORT IO, Fmt; TYPE CallBack = PROCEDURE (a: CARDINAL; b: INTEGER);     Values = REF ARRAY OF INTEGER; VAR sample := ARRAY [1..5] OF INTEGER {5, 4, 3, 2, 1};    callback := Display; PROCEDURE Display(loc: CARDINAL; val: INTEGER) =  BEGIN    IO.Put("array[" & Fmt.Int(loc) & "] = " & Fmt.Int(val * val) & "\n");  END Display; PROCEDURE Map(VAR values: ARRAY OF INTEGER; size: CARDINAL; worker: CallBack) =  VAR lvalues := NEW(Values, size);  BEGIN    FOR i := FIRST(lvalues^) TO LAST(lvalues^) DO      worker(i, values[i]);    END;  END Map; BEGIN  Map(sample, NUMBER(sample), callback);END Callback.

## Nemerle

The Nemerle.Collections namespace defines the methods Iter() (if the function applied is void) and Map() (if the function applied returns a value).

def seg = array[1, 2, 3, 5, 8, 13];def squares = seq.Map(x => x*x);

## NewLISP

> (map (fn (x) (* x x)) '(1 2 3 4))(1 4 9 16)

## Nial

each (* [first, first] ) 1 2 3 4=1 4 9 16

## Nimrod

var arr = [1,2,3,4]arr.map proc(some: var int) = echo(some, " squared = ", some*some)
Output:
 1 squared = 1
2 squared = 4
3 squared = 9
4 squared = 16


## Objeck

 use Structure; bundle Default {  class Test {    function : Main(args : String[]) ~ Nil {      Run();    }     function : native : Run() ~ Nil {      values := IntVector->New([1, 2, 3, 4, 5]);      squares := values->Apply(Square(Int) ~ Int);      each(i : squares) {        squares->Get(i)->PrintLine();      };    }     function : Square(value : Int) ~ Int {      return value * value;    }  }}

## OCaml

This function is part of the standard library:

Array.map

Usage example:

let square x = x * x;;let values = Array.init 10 ((+) 1);;Array.map square values;;

Or with lists (which are more typical in OCaml):

let values = [1;2;3;4;5;6;7;8;9;10];;List.map square values;;

Use iter if the applied function does not return a value.

Array.iter (fun x -> Printf.printf "%d" x) [|1; 2; 3; 4; 5|];;
List.iter (fun x -> Printf.printf "%d" x) [1; 2; 3; 4; 5];;

with partial application we can also write:

Array.iter (Printf.printf "%d") [|1; 2; 3; 4; 5|];;
List.iter (Printf.printf "%d") [1; 2; 3; 4; 5];;

## Octave

Almost all the built-in can operate on each element of a vector or matrix; e.g. sin([pi/2, pi, 2*pi]) computes the function sin on pi/2, pi and 2*pi (returning a vector). If a function does not accept vectors/matrices as arguments, the arrayfun can be used.

function e = f(x, y)  e = x^2 + exp(-1/(y+1));endfunction % f([2,3], [1,4]) gives and error, butarrayfun(@f, [2, 3], [1,4])% works

(The function f can be rewritten so that it can accept vectors as argument simply changing operators to their dot relatives: e = x.^2 + exp(-1 ./ (y.+1)))

## ooRexx

ooRexx doesn't directly support callbacks on array items, but this is pretty easy to implement using Routine objects.

 start = .array~of("Rick", "Mike", "David", "Mark")new = map(start, .routines~reversit)call map new, .routines~sayit  -- a function to perform an iterated callback over an array-- using the provided function.  Returns an array containing-- each function result::routine map  use strict arg array, function  resultArray = .array~new(array~items)  do item over array     resultArray~append(function~call(item))  end  return resultArray ::routine reversit  use arg string  return string~reverse ::routine sayit  use arg string  say string  return .true   -- called as a function, so a result is required

## Order

Both sequences and tuples support the usual map operation seen in many functional languages. Sequences also support 8seq_for_each, and a few variations, which returns 8nil.

#include <order/interpreter.h> ORDER_PP( 8tuple_map(8fn(8X, 8times(8X, 8X)), 8tuple(1, 2, 3, 4, 5)) )// -> (1,4,9,16,25) ORDER_PP( 8seq_map(8fn(8X, 8times(8X, 8X)), 8seq(1, 2, 3, 4, 5)) )// -> (1)(4)(9)(16)(25) ORDER_PP( 8seq_for_each(8fn(8X, 8print(8X 8comma)), 8seq(1, 2, 3, 4, 5)) )// prints 1,2,3,4,5, and returns 8nil

## Oz

declare  fun{Square A}    A*A  end   Lst = [1 2 3 4 5]   %% apply a PROCEDURE to every element  {ForAll Lst Show}   %% apply a FUNCTION to every element  Result = {Map Lst Square}  {Show Result}

## PARI/GP

Works with: PARI/GP version 2.4.2 and above
callback(n)=n+n;apply(callback, [1,2,3,4,5])

See Delphi

## Perl

# create arraymy @a = (1, 2, 3, 4, 5); # create callback functionsub mycallback {  return 2 * shift;} # use array indexingfor (my $i = 0;$i < scalar @a; $i++) { print "mycallback($a[$i]) = ", mycallback($a[$i]), "\n";} # using foreachforeach my$x (@a) {  print "mycallback($x) = ", mycallback($x), "\n";} # using map (useful for transforming an array)my @b = map mycallback($_), @a; # @b is now (2, 4, 6, 8, 10) # and the same using an anonymous functionmy @c = map {$_ * 2 } @a;                     # @c is now (2, 4, 6, 8, 10) # use a callback stored in a variablemy $func = \&mycallback;my @d = map$func->($_), @a; # @d is now (2, 4, 6, 8, 10) # filter an array my @e = grep {$_ % 2 == 0 } @a;               # @e is now (2, 4)

## Perl 6

Works with: Rakudo version #21 "Seattle"
my $function = { 2 *$^x + 3 };my @array = 1 .. 5; # via map function.say for map $function, @array; # via map method.say for @array.map($function); # via for loopfor @array {    say $function($_);} # via the "hyper" metaoperator and method indirectionsay @array».$function; ## PHP function cube($n){   return($n *$n * $n);}$a = array(1, 2, 3, 4, 5);$b = array_map("cube",$a);print_r($b); ## PicoLisp : (mapc println (1 2 3 4 5)) # Print numbers12345-> 5 : (mapcar '((N) (* N N)) (1 2 3 4 5)) # Calculate squares-> (1 4 9 16 25) : (mapcar ** (1 2 3 4 5) (2 .)) # Same, using a circular list-> (1 4 9 16 25) : (mapcar if '(T NIL T NIL) '(1 2 3 4) '(5 6 7 8)) # Conditional function-> (1 6 3 8) ## Pike int cube(int n){ return n*n*n;} array(int) a = ({ 1,2,3,4,5 });array(int) b = cube(a[*]); // automap operatorarray(int) c = map(a, cube); // conventional map function ## PL/I  declare x(5) initial (1,3,5,7,8); x = sqrt(x); x = sin(x); ## PL/SQL PL/SQL doesn't have callbacks, though we can pass around an object and use its method to simulate one. Further, this callback method can be defined in an abstract class that the mapping function will expect. -- Let's create a generic class with one method to be used as an interface:CREATE OR REPLACETYPE callback AS OBJECT ( -- A class needs at least one member even though we don't use it -- There's no generic OBJECT type, so let's call it NUMBER dummy NUMBER, -- Here's our function, and since PL/SQL doesn't have generics, -- let's use type NUMBER for our params MEMBER FUNCTION exec(n NUMBER) RETURN NUMBER) NOT FINAL NOT instantiable;/ -- Now let's inherit from that, defining a class with one method. We'll have ours square a number.-- We can pass this class into any function that takes type callback:CREATE OR REPLACE TYPE CB_SQUARE under callback ( OVERRIDING MEMBER FUNCTION exec(n NUMBER) RETURN NUMBER)/CREATE OR REPLACETYPE BODY CB_SQUARE AS OVERRIDING MEMBER FUNCTION exec(n NUMBER) RETURN NUMBER IS BEGIN RETURN n * n; END exec;END;/ -- And a package to hold our testCREATE OR REPLACE PACKAGE PKG_CALLBACK AS myCallback cb_square; TYPE intTable IS TABLE OF NUMBER INDEX BY BINARY_INTEGER; ints intTable; i PLS_INTEGER; PROCEDURE test_callback;END PKG_CALLBACK;/ CREATE OR REPLACE PACKAGE BODY PKG_CALLBACK AS -- Our generic mapping function that takes a "method" and a collection -- Note that it takes the generic callback type -- that doesn't know anything about squaring PROCEDURE do_callback(myCallback IN callback, ints IN OUT intTable) IS i PLS_INTEGER; myInt NUMBER; BEGIN FOR i IN 1 .. ints.COUNT LOOP myInt := ints(i); -- PL/SQL call's the child's method ints(i) := myCallback.exec(myInt); END LOOP; END do_callback; PROCEDURE test_callback IS BEGIN myCallback := cb_square(NULL); FOR i IN 1..5 LOOP ints(i) := i; END LOOP; do_callback(myCallback, ints); i := ints.FIRST; WHILE i IS NOT NULL LOOP DBMS_OUTPUT.put_line(ints(i)); i := ints.next(i); END LOOP; END test_callback;END PKG_CALLBACK;/ BEGIN PKG_CALLBACK.TEST_CALLBACK();END;/ ## Pop11 ;;; Define a proceduredefine proc(x); printf(x*x, '%p,');enddefine; ;;; Create arraylvars ar = { 1 2 3 4 5}; ;;; Apply procedure to arrayappdata(ar, proc); If one wants to create a new array consisting of transformed values then procedure mapdata may be more convenient. ## PostScript The forall operator applies a procedure to each element of an array, a packed array or a string. [1 2 3 4 5] { dup mul = } forall In this case the respective square numbers for the elements are printed. To create a new array from the results above code can simply be wrapped in []: [ [1 2 3 4 5] { dup mul } forall ] Library: initlib  [1 2 3 4 5] {dup *} map  ## PowerShell This can be done in PowerShell with the ForEach-Object cmdlet which applies a scriptblock to each element of an array: 1..5 | ForEach-Object {$_ * $_ } To recreate a map function, found in other languages the same method applies: function map ([array]$a, [scriptblock] $s) {$a | ForEach-Object $s} ## Prolog Prolog doesn't have arrays, but we can do it with lists. This can be done in the console mode.  ?- assert((fun(X, Y) :- Y is 2 * X)).true. ?- maplist(fun, [1,2,3,4,5], L).L = [2,4,6,8,10].  ## PureBasic Procedure Cube(Array param.i(1)) Protected n.i For n = 0 To ArraySize(param()) Debug Str(param(n)) + "^3 = " + Str(param(n) * param(n) * param(n)) Next EndProcedure Dim AnArray.i(4) For n = 0 To ArraySize(AnArray()) AnArray(n) = Random(99)Next Cube(AnArray())  ## Python def square(n): return n * n numbers = [1, 3, 5, 7] squares1 = [square(n) for n in numbers] # list comprehension squares2a = map(square, numbers) # functional form squares2b = map(lambda x: x*x, numbers) # functional form with lambda squares3 = [n * n for n in numbers] # no need for a function, # anonymous or otherwise isquares1 = (n * n for n in numbers) # iterator, lazy import itertoolsisquares2 = itertools.imap(square, numbers) # iterator, lazy To print squares of integers in the range from 0 to 9, type: print " ".join(str(n * n) for n in range(10)) Or: print " ".join(map(str, map(square, range(10)))) Result: 0 1 4 9 16 25 36 49 64 81 ## R Many functions can take advantage of implicit vectorisation, e.g. cube <- function(x) x*x*xelements <- 1:5cubes <- cube(elements) Explicit looping over array elements is also possible. cubes <- numeric(5)for(i in seq_along(cubes)){ cubes[i] <- cube(elements[i])} Loop syntax can often simplified using the *apply family of functions. elements2 <- list(1,2,3,4,5)cubes <- sapply(elements2, cube) In each case above, the value of 'cubes' is 1 8 27 64 125  ## Racket  #lang racket ;; using the for/vector' comprehension form(for/vector ([i #(1 2 3 4 5)]) (sqr i)) ;; the usual functional map'(vector-map sqr #(1 2 3 4 5))  ## Raven # To print the squared elements[1 2 3 4 5] each dup * print # To obtain a new arraygroup [1 2 3 4 5] each dup *list ## REBOL rebol [ Title: "Array Callback" Date: 2010-01-04 Author: oofoe URL: http://rosettacode.org/wiki/Apply_a_callback_to_an_Array] map: func [ "Apply a function across an array." f [native! function!] "Function to apply to each element of array." a [block!] "Array to process." /local x][x: copy [] forall a [append x do [f a/1]] x] square: func [x][x * x] ; Tests: assert: func [code][print [either do code [" ok"]["FAIL"] mold code]] print "Simple loop, modify in place:"assert [[1 100 81] = (a: [1 10 9] forall a [a/1: square a/1] a)] print [crlf "Functional style with 'map':"]assert [[4 16 36] = map :square [2 4 6]] print [crlf "Applying native function with 'map':"]assert [[2 4 6] = map :square-root [4 16 36]] Output: Simple loop, modify in place: ok [[1 100 81] = (a: [1 100 81] forall a [a/1: square a/1] a)] Functional style with 'map': ok [[4 16 36] = map :square [2 4 6]] Applying native function with 'map': ok [[2 4 6] = map :square-root [4 16 36]] ## Retro Using the array' library to multiply each value in an array by 10 and display the results: [ 1 2 3 4 5 ] ^array'fromQuote [ 10 * ] ^array'map ^array'display Retro also provides ^array'apply for use when you don't want to alter the contents of the array: [ "Hello" "World" "Foo" ] ^array'fromQuote [ "%s " puts ] ^array'apply ## REXX /*REXX program to apply a callback to a stemmed (REXX) array. */ a.=; b.= a.0= 0 a.1= 1 a.2= 2 a.3= 3 a.4= 4 a.5= 5 a.6= 6 a.7= 7 a.8= 8 a.9= 9a.10=10 call listab 'before'call bangit 'a','b' /*factorialize the A array, store results in B */call listab ' after'exit /*stick a fork in it, we're done.*//*──────────────────────────────────BANGIT subroutine───────────────────*/bangit: do i=0 _=value(arg(1)'.'i); if _=='' then return call value arg(2)'.'i,fact(_) end /*i*//*──────────────────────────────────FACT subroutine─────────────────────*/fact: procedure; !=1; do j=2 to arg(1); !=!*j; end; return !/*──────────────────────────────────LISTAB subroutine───────────────────*/listab: do j=0 while a.j\==''; say arg(1) 'a.'j"="a.j; end /*j*/say; do k=0 while b.k\==''; say arg(1) 'b.'k"="b.k; end /*k*/return output before a.0=0 before a.1=1 before a.2=2 before a.3=3 before a.4=4 before a.5=5 before a.6=6 before a.7=7 before a.8=8 before a.9=9 before a.10=10 after a.0=0 after a.1=1 after a.2=2 after a.3=3 after a.4=4 after a.5=5 after a.6=6 after a.7=7 after a.8=8 after a.9=9 after a.10=10 after b.0=1 after b.1=1 after b.2=2 after b.3=6 after b.4=24 after b.5=120 after b.6=720 after b.7=5040 after b.8=40320 after b.9=362880 after b.10=3628800  ## RLaB RLaB has two type of arrays: 'standard' or 1-dimensional, that can be a row- or a column-vectory; and, 'associative' which are called lists. For standard array its entry identifier (index) is an integer in range 1:N where N is the size of the array. For associative array its entry identifier is a string consisting of printable ASCII characters. All scalar mathematical functions are 'matrix-optimized' meaning that if the argument to a function is a matrix, then the return value of the function is a matrix of the same size as the input argument, where the function is applied to the individual entries of the matrix. Consider an example:  >> x = rand(2,4) 0.707213207 0.275298961 0.396757763 0.232312312 0.215619868 0.207078017 0.565700032 0.666090571>> sin(x) 0.649717845 0.271834652 0.386430003 0.230228332 0.213952984 0.205601224 0.536006923 0.617916954  This can be done on entry-by-entry basis, but one has to keep in mind that the 'for' or 'while' loops are slow in interpreted languages, and RLaB is no exception.  x = rand(2,4);y = zeros(2,4);for (i in 1:2){ for (j in 1:4) { y[i;j] = sin( x[i;j] ); }}  The functions can take lists as arguments, but then it has to be specified within the body of the function what to do with the list elements. Given a list call it 'x' there is a RLaB function 'members' which returns a string vector with the names of the elements of the list.  x = <<>>;for (i in 1:9){ x.[i] = rand();} y = <<>>;for (i in members(x)){ y.[i] = sin( x.[i] );}  ## Ruby You could use a traditional "for i in arr" approach like below: for i in [1,2,3,4,5] do puts i**2end Or you could the more preferred ruby way of an iterator (which is borrowed from SmallTalk) [1,2,3,4,5].each{ |i| puts i**2 } To create a new array of each value squared [1,2,3,4,5].map{ |i| i**2 } ## Salmon These examples apply the square function to a list of the numbers from 0 through 9 to produce a new list of their squares, then iterate over the resulting list and print the squares. function apply(list, ageless to_apply) (comprehend(x; list) (to_apply(x))); function square(x) (x*x); iterate(x; apply([0...9], square)) x!; With short identifiers: include "short.salm"; fun apply(list, ageless to_apply) (comp(x; list) (to_apply(x))); fun square(x) (x*x); iter(x; apply([0...9], square)) x!; With the numbers given as a list of individual elements: function apply(list, to_apply) (comprehend(x; list) (to_apply(x))); function square(x) (x*x); iterate(x; apply([0, 1, 2, 3, 4, 5, 6, 7, 8, 9], square)) x!; ## Sather class MAIN is do_something(i:INT):INT is return i * i; end; main is a:ARRAY{INT} := |1, 2, 3, 4, 5|; -- we use an anonymous closure to apply our do_something "callback" a.map(bind(do_something(_))); loop #OUT + a.elt! + "\n"; end; end;end; ## Scala val l = List(1,2,3,4)l.foreach {i => println(i)} When the argument appears only once -as here, i appears only one in println(i) - it may be shortened to l.foreach(println(_)) Same for an array val a = Array(1,2,3,4)a.foreach {i => println(i)}a.foreach(println(_)) '' // same as previous line'' Or for an externally defined function: def doSomething(in: int) = {println("Doing something with "+in)}l.foreach(doSomething) There is also a for syntax, which is internally rewritten to call foreach. A foreach method must be defined on a for(val i <- a) println(i) It is also possible to apply a function on each item of an list to get a new list (same on array and most collections) val squares = l.map{i => i * i} ''//squares is'' List(1,4,9,16) Or the equivalent for syntax, with the additional keyword yield, map is called instead of foreach val squares = for (val i <- l) yield i * i ## Scheme (define (square n) (* n n))(define x #(1 2 3 4 5))(map square (vector->list x)) A single-line variation (map (lambda (n) (* n n)) '(1 2 3 4 5)) For completeness, the map function (which is R5RS standard) can be coded as follows: (define (map f L) (if (null? L) L (cons (f (car L)) (map f (cdr L))))) ## Sidef Define a callback function: func callback(i) { say i**2 }; Now, the function will get called for each element: [1,2,3,4].each(callback); Same as above, but with the function inlined: [1,2,3,4].each{|i| say i**2 }; To create a new array of each value squared, we can use: [1,2,3,4,5].map{|i| i**2 }; ## Slate #( 1 2 3 4 5 ) collect: [| :n | n * n]. ## Smalltalk #( 1 2 3 4 5 ) collect: [:n | n * n]. ## Sparkling The foreach function calls the supplied callback on each element of the (possibly associative) array, passing it each key and the corresponding value: let numbers = { 1, 2, 3, 4 };foreach(numbers, function(idx, num) { print(num);}); The map function applies the transform to each key-value pair and constructs a new array, of which the keys are the keys of the original array, and the corresponding values are the return values of each call to the transform function: let dict = { "foo": 42, "bar": 13, "baz": 37 };let doubled = map(dict, function(key, val) { return val * 2;}); ## Standard ML  map f l  i.e.  map (fn x=>x+1) [1,2,3];; (* [2,3,4] *)  ## SuperCollider Actually, there is a builtin squared operator: [1, 2, 3].squared; // returns [1, 4, 9] Anything that is a Collection can be used with collect: [1, 2, 3].collect({ arg x; x*x }); List comprehension combined with a higher-order function can also be used: var square = { arg x; x*x;};var map = { arg fn, xs; all {: fn.value(x), x <- xs };};map.value(square,[1,2,3]); ## Swift func square(n: Int) -> Int { return n * n} let numbers = [1, 3, 5, 7] let squares1a = numbers.map(square) // map method on array let squares1b = numbers.map {x in x*x} // map method on array with anonymous function let squares2a = map(numbers, square) // map function let squares2b = map(numbers) {x in x*x} // map function with anonymous function let isquares1 = lazy(numbers).map(square) // lazy sequence ## Tcl If I wanted to call "myfunc" on each element of dat and dat were a list: foreach var$dat {    myfunc $var} This does not retain any of the values returned by myfunc. if dat were an (associative) array, however: foreach name [array names dat] { myfunc$dat($name)} More functional, with a simple map function: proc map {f list} { set res {} foreach e$list {lappend res [$f$e]}   return $res}proc square x {expr {$x*$x}} % map square {1 2 3 4 5}1 4 9 16 25 ## TI-89 BASIC © For no return valueDefine foreach(fe_cname,fe_list) = Prgm Local fe_i For fe_i,1,dim(fe_list) #fe_cname(fe_list[fe_i]) EndForEndPrgm © For a list of resultsDefine map(map_cnam,map_list) = seq(#map_cnam(map_list[map_i]),map_i,1,dim(map_list)) Define callback(elem) = Prgm Disp elemEndPrgm foreach("callback", {1,2,3,4,5})Disp map("√", {1,2,3,4,5}) Output: 1 2 3 4 5 $\begin{Bmatrix}1 & \sqrt{2} & \sqrt{3} & 2 & \sqrt{5}\end{Bmatrix}$ ## TIScript JavaScript alike: var a = [1, 2, 3, 4, 5];a.map(function(v) { return v * v; })  Using short form of lambda notation: var a = [1, 2, 3, 4, 5];a.map( :v: v*v );  ## Toka ( array count function -- ){ value| array fn | [ i array ] is I [ to fn swap to array 0 swap [ I array.get :stack fn invoke I array.put ] countedLoop ]} is map-array ( Build an array )5 cells is-array a10 0 a array.put11 1 a array.put12 2 a array.put13 3 a array.put14 4 a array.put ( Add 1 to each item in the array )a 5 [ 1 + ] map-array ## TorqueScript --Elm 03:41, 18 June 2012 (UTC) Callbacks:  function map(%array,%arrayCount,%function){ for(%i=0;%i<%arrayCount;%i++) { eval("%a = "@%array@"["@%i@"];"); eval(""@%function@"("@%a@");"); }}  Now to set up an array: $array[0] = "Hello.";$array[1] = "Hi.";$array[2] = "How are you?";

Now to call the function correctly:

 map("$array",3,"echo");  Which should result in:  => Hello. => Hi. => How are you?  ## TXR Print 1 through 10 out of a vector, using prinl the callback, right from the system shell command prompt: $ txr -e '[mapdo prinl #(1 2 3 4 5 6 7 8 9 10)]'12345678910

mapdo is like mapcar but doesn't accumulate a list, suitable for imperative programming situations when the function is invoked to perform a side effect.

TXR extends Lisp list processing primitives to work with vectors and strings also, which is why mapdo cheerfully traverses a vector.

## UNIX Shell

Works with: Bourne Shell
map() {	map_command=$1 shift for i do "$map_command" "$i"; done}list=1:2:3(IFS=:; map echo$list)
Works with: ksh93
Works with: pdksh
Works with: zsh
map() {	typeset command=$1 shift for i do "$command" "$i"; done}set -A ary 1 2 3map print "${ary[@]}"
Works with: zsh
map(){for i ($*[2,-1])$1 $i}a=(1 2 3)map print$a

## Ursala

The * is a built-in map operator. This example shows a map of the successor function over a list of natural numbers.

#import nat #cast %nL demo = successor* <325,32,67,1,3,7,315>

output:

<326,33,68,2,4,8,316>


## V

apply squaring (dup *) to each member of collection

[1 2 3 4] [dup *] map

## VBScript

I really have my doubts as to whether this really counts as a callback. I used the same thing in the solution to Amb.

##### Implementation
 class callback	dim sRule 	public property let rule( x )		sRule = x	end property 	public default function applyTo(a)		dim p1		for i = lbound( a ) to ubound( a )			p1 = a( i )			a( i ) = eval( sRule )		next		applyTo = a	end functionend class
##### Invocation
 dim a1dim cbset cb = new callback cb.rule = "ucase(p1)"a1 = split("my dog has fleas", " " )cb.applyTo a1wscript.echo join( a1, " " ) cb.rule = "p1 ^ p1"a1 = array(1,2,3,4,5,6,7,8,9,10)cb.applyto a1wscript.echo join( a1, ", " )
##### Output
MY DOG HAS FLEAS
1, 4, 27, 256, 3125, 46656, 823543, 16777216, 387420489, 10000000000


## Vim Script

map() works with lists and dictionaries. The second argument is an expression string where v:val is replaced by the current value and v:key by the current key (for lists the key is the index). The result of evaluating the string will be the new value. The list/dictionary is modified in place.

echo map([10, 20, 30], 'v:val * v:val')echo map([10, 20, 30], '"Element " . v:key . " = " . v:val')echo map({"a": "foo", "b": "Bar", "c": "BaZ"}, 'toupper(v:val)')echo map({"a": "foo", "b": "Bar", "c": "BaZ"}, 'toupper(v:key)')
Output:
[100, 400, 900]
['Element 0 = 10', 'Element 1 = 20', 'Element 2 = 30']
{'a': 'FOO', 'b': 'BAR', 'c': 'BAZ'}
{'a': 'A', 'b': 'B', 'c': 'C'}

## Vorpal

Given and array, A, and a function, F, mapping F over the elements of A is simple:

A.map(F)

If F takes 2 arguments, x and , then simply pass them to map. They will be passed to F when as it is applied to each element of A.

A.map(F, x, y)

## Wart

map prn '(1 2 3 4 5)

Output:

1
2
3
4
5

## zkl

L(1,2,3,4,5).apply('+(5))

Output:

L(6,7,8,9,10)