doc-src/Codegen/Thy/examples/Example.hs

try to avoid races again (cf. 8c37cb84065f and fd3a36e48b09);

{-# LANGUAGE EmptyDataDecls, RankNTypes, 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;

}