Haskell conduit filter distinct values

Question

If I use the following Source:

 sourceList [1,3,3,1,2,3]

Is it possible to apply some filter or combinator to only allow distinct values to be passed downstream?

So in my example, only [1,3,2] would be passed downstream?

Answer 1

Something like this should do:

#!/usr/bin/env stack
-- stack --resolver lts-6.19 runghc --package conduit-combinators
import Conduit
import Data.Conduit.List (sourceList)

main = do
    print $ runConduitPure $ sourceList [1,3,3,1,2,3] .| myConduit [] .| sinkList

myConduit dup = do
  num <- await
  case num of
    Just x -> if x `elem` dup
              then myConduit dup
              else do
                yield x
                myConduit (x:dup)
    Nothing -> return ()

On execution:

sibi::casey { ~/scripts }-> ./cond.hs
[1,3,2]