Map change all in Haskell

In Haskell, arrays are immutable data structures, meaning their elements cannot be modified once they are created. However, we can create a new array with the updated elements using the // operator.

The syntax to change all elements of an array is as follows:

newArray = originalArray // [(i, newValue) | i <- [0..((length originalArray)-1)]]

Here, (i, newValue) is used to represent the updated value at index i of the new array. The list comprehension [0..((length originalArray)-1)] generates a list containing all the indices of the original array, allowing us to update all elements.

Here's an example code that changes all elements of an array containing integers:

import Data.Array
main = do

    let origArray = array (0,4) [(i, i) | i <- [0..4]] -- Creates an array of size 5 

                                                      -- with the values [0, 1, 2, 3, 4]

    putStrLn "Original array: "

    print origArray

    let newArray = origArray // [(i, i*2) | i <- [0..4]] -- Creates a new array with all values

                                                        -- multiplied by 2

    putStrLn "New array: "

    print newArray

The output of this code would be:

Original array:
array (0,4) [(0,0),(1,1),(2,2),(3,3),(4,4)]
New array:
array (0,4) [(0,0),(1,2),(2,4),(3,6),(4,8)]

Note that while the original array remains unchanged, the new array has all its elements updated according to our specified logic.