Function to determine if all elements are the same

[Juan Martin Buireo]

Hi, I need to make a function and I am having some trouble.


In Haskell I know how to do it but here in Elm is differente due to the implementation of Lists.


I have a huge list and I want to check if all elements in the list are the same. I have a Haskell function that works but in Elm it doesn't because List.tail returns a Maybe (List a). So with this, i cannot do a List.map or List.all on the tail of the list.


Thanks

[Peter Damoc]

Here is one way to do it:

allTheSame xs  =

  case Set.toList(Set.fromList xs) of

    [] -> True -- or False, your choice 

    x::[] -> True 

    _ -> False


If you convert a list into a set, and the set back to a list, you will get a list with only one element for a list of identical elements 


here is another approach 

allTheSame2 xs = 

  let 

     check x rest =

       case rest of 

         [] -> True 

         y::ys -> x == y && check x ys

  in 

    case xs of 

      [] -> True -- or False 

      y::ys -> check y ys

and another approach

allTheSame3 xs = 

  let 

    f x acc = 

      if List.member x acc then acc else x::acc

  in 

    List.length (List.foldl f [] xs) <= 1  

 

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[Peter Damoc]

Actually, the most sensible would be:

allTheSame4 xs  =

  Set.size (Set.fromList xs) <=1

  

[slosh...@gmail.com]

Here's another way using List.all:

allTheSame xs =

  case xs of
    [] -> True

    y :: ys -> List.all ((==) y) ys