data HNil = HNil;
data HCons e l = HCons e l;

class HList l where {}
instance HList HNil where {}
instance HList l => HList (HCons e l) where {}

class HAppendC l l' where {
  type HAppend l l';
  hAppend :: l -> l' -> HAppend l l';
}

instance HList l => HAppendC HNil l where {
  type HAppend HNil l = l;
  hAppend x l = l;
}

instance HList l, HAppendC l l' => HAppendC (HCons x l) l' where {
  type HAppend (HCons x l) l' = HCons x (HAppend l l');
  hAppend y l' = case y of HCons x l -> HCons x (hAppend l l');;
}

list1 = HCons 42 (HCons True HNil);

list2 = HCons (1,0) (HCons False (HCons (\x -> x + 1) HNil));

main = hAppend list1 list2;