(module c2_let_alias
  (data Tree
    (doc "boxed tree")
    (ctor TLeaf)
    (ctor TNode (con Int) (con Tree) (con Tree)))
  (fn count
    (doc "alias a := borrowed t, then match a")
    (type (fn-type (params (borrow (con Tree))) (ret (own (con Int)))))
    (params t)
    (body
      (let a t
        (match a
          (case (pat-ctor TLeaf) 0)
          (case (pat-ctor TNode v l r) 1))))))