(IN HASKELL) Declare the type and define a function (say fun) that takes a list

Question

(IN HASKELL)

Declare the type and define a function (say fun) that takes a list of natural numbers (say ns) and a number (say n) as input. Then the program returns a list of numbers that contains only the multiples of number n from the input list. for instance,                  fun [11, 12, 4, 9, 15, 21, 3, 5] 3          gives this list back       [12, 9, 15, 21, 3]   because they are multiple of 3.

Write two versions of this program: in one version use list comprehension technique, and in the other version use recursion.

Explanation / Answer

(IN HASKELL)

Declare the type and define a function (say fun) that takes a list of natural numbers (say ns) and a number (say n) as input. Then the program returns a list of numbers that contains only the multiples of number n from the input list. for instance,                  fun [11, 12, 4, 9, 15, 21, 3, 5] 3          gives this list back       [12, 9, 15, 21, 3]   because they are multiple of 3.

Write two versions of this program: in one version use list comprehension technique, and in the other version use recursion.

Ans:

comprehension technique:

Fun : : [Integer] ->[Integer] - > Integer

                Fun ns n [x x < - ns, x ‘mod’ n]

using recursion.

Fun : : [Integer] ->[Integer] - > Integer

Fun ns n filter(ns ‘mod’ n)

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