Rosetta Code

Apply a callback to an array

Revision as of 22:48, 22 August 2007 by rosettacode>TucRup

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

Ada

Tested With: 

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;

C

Tested With:

  • GCC 3.3.6
    • i686-pc-linux-gnu
  • GCC 3.4.6
    • i686-pc-linux-gnu
  • GCC 4.0.3
    • i686-pc-linux-gnu
  • GCC 4.1.1
    • i686-pc-linux-gnu
    • powerpc-unknown-linux-gnu
  • TCC 0.9.23
    • i686-pc-linux-gnu
  • ICC 9.1
    • i686-pc-linux-gnu

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#

Platform: .NET

Language Version: 2.0

Compiler: Visual C# 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);
  }
}

C

Compiler: GNU Compiler Collection 4.1.1

Using 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

Using std::vector 

#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

Using Boost.Lambda 

 using namespace std;
 using namespace boost::lambda;
 vector<int> ary(10);
 int i = 0;
 for_each(ary.begin(), ary.end(), _1 =   var(i)); // init array
 transform(ary.begin(), ary.end(), ostream_iterator<int>(cout, " "), _1 * _1); // square and output

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

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*)

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 builtin 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))

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

      program test
C
C--   Declare array:
      integer a(5)
C
C--   Fill it with Data
      data a /45,22,67,87,98/
C
C--   Do something with all elements (in this case: print their squares)
      do i=1,5
        print *,a(i)*a(i)
      end do
C
      end


FP

Interpreter : "fp" 

 {square * . [id, id]}
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