Solution 3 for Project Euler problem 1 written in Elm

App.elm

-- we will show the result with a single html text node
import Html exposing (text)

-- let's call the function euler1 and say it receives a single Int param and returns a single Int param
euler1 : Int -> Int
euler1 num =
  -- no recursion this time, only lists
  let
    -- create a list with numbers from 1 to num - 1
    list = [1..num-1]
    -- remove all of the numbers in the list which are not divisable by 3 or 5
    list2 = List.filter (\num -> num % 3 == 0 || num % 5 ==0) list
  in
    -- return the sum of all of the good numbers
    List.sum list2
    
main =
  -- convert from String to Int and show the result with a text node
  -- param = 10 because we need to get the sum of all the numbers below 10 that pass the test
  text ( toString ( euler1 10 ) )