(************************************************************
   counter.ml		Created      : Fri Aug  8 20:16:18 2003
  			Last modified: Fri Aug 08 21:00:17 2003
  Compile: ocamlc counter.ml -o counter #
  FTP Directory: sources/ocaml #
************************************************************)
(**
型エラーを起こします。

File "counter.ml", line 8, characters 28-70:
This expression has type int * (unit -> int * (unit -> 'a))
but is here used with type int * (unit -> 'a)

Unify 時に occur check で引っかかる。 Unify((int * (unit -> 'a)),  'a)
再帰型を許していないので、こんな関数はかけない。そこで... (counter2.ml に続く)
*)

let rec counter_new init = (init, (fun () -> (counter_new (init + 1))))
let counter_value (v, _) = v
let counter_increment (_, f) = f ()