reverted to join_bodies/join_proofs based on fold_body_thms to regain performance (escpecially of HOL-Proofs) -- see also aa9c1e9ef2ce and 4e2abb045eac;
{-# LANGUAGE ScopedTypeVariables #-}
module Example where {
data Queue a = AQueue [a] [a];
empty :: forall a. Queue a;
empty = AQueue [] [];
dequeue :: forall a. Queue a -> (Maybe a, Queue a);
dequeue (AQueue [] []) = (Nothing, AQueue [] []);
dequeue (AQueue xs (y : ys)) = (Just y, AQueue xs ys);
dequeue (AQueue (v : va) []) =
let {
(y : ys) = reverse (v : va);
} in (Just y, AQueue [] ys);
enqueue :: forall a. a -> Queue a -> Queue a;
enqueue x (AQueue xs ys) = AQueue (x : xs) ys;
}