(module m
  (data Expr (ctor Lit (con Int)) (ctor Add (con Expr) (con Expr)) (ctor Mul (con Expr) (con Expr)))
  (fn eval
    (type (fn-type (params (own (con Expr))) (ret (own (con Int)))))
    (params e)
    (body
      (match e
        (case (pat-ctor Lit n) n)
        (case (pat-ctor Add a b) (app + (app eval a) (app eval b)))
        (case (pat-ctor Mul a b) (app * (app eval a) (app eval b))))))
  (fn main
    (type (fn-type (params) (ret (own (con Unit))) (effects IO)))
    (params)
    (body
      (let e (term-ctor Expr Mul (term-ctor Expr Add (term-ctor Expr Lit 2) (term-ctor Expr Lit 3)) (term-ctor Expr Lit 4))
        (seq (app print (app eval e)) (do io/print_str "\n"))))))