Created
May 3, 2014 15:03
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| (** Run: | |
| coretop existential.ml | |
| *) | |
| open Core.Std | |
| type ('a, 'b) entity = { | |
| id : unit -> string; | |
| step : 'b -> 'b some_entity; | |
| to_string : unit -> string; | |
| } and 'b some_entity = | |
| | Some_entity : ('a, 'b) entity -> 'b some_entity | |
| let rec make_entity ~id ~step ~to_string ~state = | |
| let step x = | |
| let state = step state x in | |
| make_entity ~id ~to_string ~step ~state | |
| in | |
| let id () = id state in | |
| let to_string () = to_string state in | |
| Some_entity { id; to_string; step; } | |
| ;; | |
| let make_sum_entity ~init = | |
| make_entity | |
| ~state:init | |
| ~id:(Fn.const "sum") | |
| ~to_string:Int.to_string | |
| ~step:(fun state i -> i + state) | |
| ;; | |
| let make_cons_entity ~init = | |
| make_entity | |
| ~state:init | |
| ~id:(Fn.const "cons") | |
| ~to_string:(fun is -> | |
| (String.concat ~sep:", " | |
| (List.map ~f:Int.to_string is))) | |
| ~step:(fun state i -> i :: state) | |
| ;; | |
| let print_entities entities = | |
| List.iteri entities ~f:(fun i (Some_entity entity) -> | |
| Printf.printf "#%d: %s\n" i (entity.to_string ())) | |
| ;; | |
| let main () = | |
| let entities = | |
| [ make_sum_entity ~init:0 | |
| ; make_cons_entity ~init:[] | |
| ] | |
| in | |
| print_entities entities; | |
| let (_ : _ some_entity list) = | |
| List.fold_left ~init:entities (List.init 3 ~f:Fn.id) | |
| ~f:(fun entities i -> | |
| let entities = | |
| List.map entities ~f:(fun (Some_entity entity) -> | |
| entity.step i) | |
| in | |
| print_entities entities; | |
| entities) | |
| in | |
| () | |
| ;; | |
| let () = main ();; |
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