diff --git a/byg/src/Function.hs b/byg/src/Function.hs
index 5d2b208..f55f5dd 100644
--- a/byg/src/Function.hs
+++ b/byg/src/Function.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE GADTs #-}
 {-# LANGUAGE FunctionalDependencies #-}
 module Function
   ( concatStrings
@@ -78,19 +79,19 @@ lowerString :: TokenableTo String a => a -> DepGenM (Token String)
 lowerString a = runFunction LowerString =<< toToken a
 
 
-class WitnessFor w t | w -> t where
-  emptyValue :: w -> t
+class (Show w, Lift w) => WitnessFor w t | w -> t
 
-data StringType = StringType
-instance WitnessFor StringType String where
-  emptyValue StringType = ""
+data StringType = StringType deriving (Show, Lift)
+instance WitnessFor StringType String
 
-data ElemOf a = ElemOf a deriving (Show, Lift)
+data ElemOf a where ElemOf :: WitnessFor w a => w -> ElemOf a
+deriving instance Show (ElemOf a)
+deriving instance Lift (ElemOf a)
 instance (Show a, Lift a, Valuable a, Eq a) => IsFunction (ElemOf a) (a, [a]) Bool where
   evalFunction (ElemOf _) (y, ys) = y `elem` ys
 
 elemOf :: (Show t, Lift t, Valuable t, Eq t, TokenableTo t a, TokenableTo [t] b, WitnessFor w t) => w -> a -> b -> DepGenM (Token Bool)
-elemOf witness a b = runFunction (ElemOf (emptyValue witness)) =<< toTupleToken a b
+elemOf witness a b = runFunction (ElemOf witness) =<< toTupleToken a b
 
 elemOfString :: (TokenableTo String a, TokenableTo [String] b) => a -> b -> DepGenM (Token Bool)
 elemOfString = elemOf StringType