{- Beispielfunktionen mit newName und mkName  -}

import Language.Haskell.TH

-- allgemeine Projektion von n-Tupel auf i-te Komponente
sel1 :: Int -> Int -> Q Exp 
sel1 i n  = do x <- newName "a" 
           {-  let wilds = replicate n WildP
               return (LamE [TupP (replaceAt (i-1) wilds (VarP x))] 
                         (VarE x))
           -}
               let wilds = replicate n wildP
               lamE [tupP (replaceAt (i-1) wilds (varP x))] 
                         (varE x)
                         
replaceAt :: Int -> [a] -> a -> [a]
replaceAt n xs x = take n xs  ++ x:drop (n+1) xs 



sel2 :: Int -> Int -> Q Exp 
sel2 i n = lamE [pat] rhs
    where pat = tupP (map (varP.mkName) as)
          rhs = varE $ mkName (as !! (i - 1))
          as  = [ "a" ++ show j | j <- [1..n] ]   



-- Erzeugung eines n-Tupels aus einer Liste 
tuple :: Int -> ExpQ
tuple n = [|\list -> $(tupE (exprs [|list|])) |]
  where
    exprs list = [infixE (Just (list))
                         (varE (mkName "!!"))
                         (Just (litE $ integerL (toInteger num)))
                    | num <- [0..(n - 1)]]