Step by Step solution about How to resolve the algorithm Averages/Arithmetic mean step by step in the Haskell programming language

The Haskell code calculates the mean (average) of a list of numbers.
The mean function takes a list of fractional numbers and returns a fractional number. If the input list is empty, the function returns 0. Otherwise, it returns the sum of the numbers in the list divided by the length of the list.

The meanReals function is similar to the mean function, but it takes a list of real numbers and returns a fractional number. It uses the mean function to calculate the mean of the real numbers, but first converts the real numbers to fractional numbers using the realToFrac function.

The third definition of the mean function uses the foldl' function to calculate the sum and length of the list in a single pass. It takes a list of real numbers and returns a fractional number. The foldl' function takes a function, an initial value, and a list, and applies the function to each element in the list, passing the result of the previous application as the first argument to the next application. In this case, the function is defined as a lambda expression that takes the current sum and length of the list, and returns a tuple of the new sum and length after adding the current element to the sum and incrementing the length. The initial value is a tuple of 0 and 0.

The main function calls the mean function with a list of numbers from 1 to 100, and prints the result.

mean :: (Fractional a) => [a] -> a
mean [] = 0
mean xs = sum xs / Data.List.genericLength xs


meanReals :: (Real a, Fractional b) => [a] -> b
meanReals = mean . map realToFrac


{-# LANGUAGE BangPatterns #-}

import Data.List (foldl') --'

mean
  :: (Real n, Fractional m)
  => [n] -> m
mean xs =
  let (s, l) =
        foldl' --'
          f
          (0, 0)
          xs
  in realToFrac s / l
  where
    f (!s, !l) x = (s + x, l + 1)

main :: IO ()
main = print $ mean [1 .. 100]