Question

Write a Haskell function (named toDigits) that accepts an integer as the parameter, and if the integer is positive then it breaks it into its digits and the output is a list of digits. On the other hand, if the input is not a positive integer, the function returns an empty list. Use the following examples to test your function:

(a) toDigits 6724 gives output [6,7,2,4]

(b) toDigits 0 gives output []

(c) toDigits -17 gives output []

Answer 1

The Haskell function 'toDigits' converts a positive integer into a list of its digits using string manipulation, returning an empty list for non-positive integers.

Step-by-step explanation:

The Haskell function toDigits should convert a positive integer into a list of its digits. If the input is zero or a negative number, it should return an empty list. Below is a possible implementation of the toDigits function:

toDigits :: Integer -> [Integer]
toDigits n
| n > 0 = map (read . (:[])) . show $ n
| otherwise = []

To walk through the logic:

• The function checks whether the input integer n is positive.
• If n is positive, it converts the integer to a string using show, then maps over each character of the string.
• For each character, it creates a singleton list (using (:[])) and then reads it back into an integer.
• If n is not positive, the function returns an empty list.

This function works correctly based on the provided examples:

1. toDigits 6724 returns [6,7,2,4]
2. toDigits 0 returns []
3. toDigits -17 returns []