Example 14 from "Logical Types for Untyped Languages" translated to OCaml

ex14.ml

type top = N of int | S of string
 
let f input extra =
  match input,extra with
  | N m, (N n,_) -> m + n
  | _, (N n,_) -> (match input with
                   | S s -> String.length s + n)
  | _,_ -> 0

let main i e = f i e

(* Error message received from MoCHi:
Verification result
Fatal error: Not implemented (Type_decl.get_base_types)
*)