Three integers to a list. Note that you have to add type annotations for nearly everything to avoid ambiguities >>> polyvariadic mempty (id :: [Int] -> [Int]) (1::Int) (2::Int) (3::Int) :: [Int]

The classic printf function, which takes an arbitrary amount of arguments and inserts them in a string:

{--}
{--}
{--}
import Data.Function.Polyvariadic
import Data.Accumulator

magicChar = '%'
notMagicChar = (/= magicChar)

data PrintfAccum = PrintfAccum { done :: String, todo :: String }

instance Show x => Accumulator PrintfAccum x where
  accumulate x (PrintfAccum done (_:todo)) = PrintfAccum
                                              (done ++ show x ++ takeWhile notMagicChar todo)
                                              (dropWhile notMagicChar todo)
  accumulate _ acc = acc

printf' str = polyvariadic
               (PrintfAccum (takeWhile notMagicChar str) (dropWhile notMagicChar str))
               done

>>> printf' "aaa%bbb%ccc%ddd" "TEST" 123 True
"aaa\"TEST\"bbb123cccTrueddd"

>>> apply ((+) :: Int -> Int -> Int) ([1,2] :: [Int]) :: Int
3