Using the Functorial interface to HashTbl

gistfile1.ml

 (* ( 'cs, 'conditions, 'actions, 'ns) *)
(* given a current state (cs)
 * and condition - get the resulting actions and next state ('ns) *)

type 'a state = State of 'a ;;
type ('cs, 'cond, 'action, 'ns) st_entry = ST_Entry of ('cs * 'cond * 'action * 'ns);;
type state_list = st_entry list ;;
type ('cs, 'cond) st_cond = State_Cond of ('cs * 'cond) ;;

type ('action, 'ns) st_action_ns = Action_NS of ('action * 'ns);;

module States = struct
  (* FILL_WSH and FILL_RNS allow for different temps for wash 
   * and rinse *)
    type t =  FILL_WSH | WASH | EMPTY | FILL_RNS | RINSE | SPIN | STOP 
    
end ;;

(* probably need something like "signals" that can be put into expressions
 * which can be evaluated
*)
module Conditions = struct
  (*TODO: condition expressions*)
end;;

(* define a state list (declarative) *)    
let my_fsm = [(States.FILL_WSH, "full",     "water_on",   States.WASH);
              (States.WASH,     "10Minutes", "agitate",   States.EMPTY);
              (States.EMPTY,    "empty",     "drain",     States.FILL_RNS);
              (States.FILL_RNS, "full",      "water_on",  States.RINSE);
              (States.RINSE,    "10Minutes", "agitate",   States.EMPTY);
              (States.EMPTY,    "empty",     "drain",     States.SPIN);
              (States.SPIN,     "5Minutes",  "motor_on",  States.STOP);
              (States.STOP,     "*",         "motor_off", States.STOP);
             ];;


module ST_Table = Hashtbl.Make(
    struct
      type t = States.t
      let equal = (=)
      let hash  = Hashtbl.hash
    end 
);;
(* 
module ST_Table :
  sig
    type key = States.t
    type 'a t
    val create : int -> 'a t
    val clear : 'a t -> unit
    val copy : 'a t -> 'a t
    val add : 'a t -> key -> 'a -> unit
    val remove : 'a t -> key -> unit
    val find : 'a t -> key -> 'a
    val find_all : 'a t -> key -> 'a list
    val replace : 'a t -> key -> 'a -> unit
    val mem : 'a t -> key -> bool
    val iter : (key -> 'a -> unit) -> 'a t -> unit
    val fold : (key -> 'a -> 'b -> 'b) -> 'a t -> 'b -> 'b
    val length : 'a t -> int
  end
*) 

let sh = ST_Table.create 5 ;; (* what if instead of '4' you could determine the number of options in States? *)
(* val sh : '_a ST_Table.t = <abstr> *)




(* now we build it from my_fsm list instead
ST_Table.add sh States.FILL ("full", States.WASH);; 
ST_Table.add sh States.WASH ("after 10 minutes", States.EMPTY);;
ST_Table.add sh States.EMPTY ("empty", States.RINSE);;
ST_Table.add sh States.RINSE ("empty", States.SPIN);;
ST_Table.add sh States.SPIN  ("after 5 minutes", States.STOP);;
*)

let _ = List.iter (fun (cs, cond, action, ns) ->  ST_Table.add sh cs (cond, action, ns)) my_fsm;;


ST_Table.find_all sh States.FILL_WSH ;;

Actually, in the REPL that's not needed, so I should remove it - the gist is setup for cut&paste into the REPL that's why the lines end with ';;'. Outside of the REPL you'd need that 'let _ = ' or 'let () =' as that's an imperative statement that you want to run right as you hit it. I think you'd actually need: 'let () = ... do something ... in' If it were in an 'if' statement, you could do something like: if condition then ( do_thing1; do_thing2; do_final_thing) else do_something (the point being the single semicolon separating those do_things statements) I suspect you could do similar things outside of the if statement and use a single semicolon instead of the 'let _ = do_something' Phil

…

On Wed, Dec 7, 2011 at 12:31 AM, Matt Youell ***@***.*** wrote: What's `let _ =` all about? --- Reply to this email directly or view it on GitHub: https://gist.github.com/1425225

Ah, thanks for explaining!