[Haskell-cafe] Tuple

[Rob Nikander]

On Sun, Apr 10, 2011 at 12:49 PM, Anwar Bari <noor2004 at yahoo.com> wrote:
> HI Cafe
>     I have to make a function to check that I have one occurrence of the last
> element (z) of the same list [a,b] in the tuple
>
>  [([a,b],z)]
> For example
> [([1,2],3),([1,1],5),([1,3],6).......]  this is true because there is one single
> z for each single list.
>
> while this one is false
> [([1,2],3),([1,2],5),([1,3],6).......] because 3&5 were found for the same list
> [1,2]
>
> any Idea how to code this Fn.
> Thanks

This seems to work...

    import Data.List

    a = [([1,2],3),([1,1],5),([1,3],6)]
    b = [([1,2],3),([1,2],5),([1,3],6)]

    test :: Ord a => [([a], a)] -> Bool
    test = not . hasDuplicates . sort
      where hasDuplicates [] = False
            hasDuplicates [_] = False
            hasDuplicates (x:xs) = fst x == fst (head xs) || hasDuplicates xs

    main = do
      print $ test a
      print $ test b


Rob