我以前在C++和Java中编写过一些状态机,但从未在像Ocaml这样的函数式语言中编写过。
问题是我不知道是否可以只是改编自面向对象语言版本的代码,因为在Ocaml中,记录和变体比类更强大;
因此,我需要一个基于事件驱动的有限状态机(分层的,就像UML中的那样),易于配置。
能否有经验的人发布一个简单的示例?只是为了避免最常见的陷阱。
谢谢 :)
编辑 16/03:是否可能不使用可变状态来实现?并且我想将其适当地封装在名称为“FSM”的模块或类下,我应该选择哪个?
我以前在C++和Java中编写过一些状态机,但从未在像Ocaml这样的函数式语言中编写过。
问题是我不知道是否可以只是改编自面向对象语言版本的代码,因为在Ocaml中,记录和变体比类更强大;
因此,我需要一个基于事件驱动的有限状态机(分层的,就像UML中的那样),易于配置。
能否有经验的人发布一个简单的示例?只是为了避免最常见的陷阱。
谢谢 :)
编辑 16/03:是否可能不使用可变状态来实现?并且我想将其适当地封装在名称为“FSM”的模块或类下,我应该选择哪个?
这取决于您必须如何操作FSM,例如,如果您需要能够存储其状态并稍后继续,或者如果您只想立即执行它。在后一种情况下,将其作为一堆尾递归函数执行是微不足道的。
例如,假设正则表达式为C((A|B)*CD)*
——以下相互递归的函数是实现FSM的直接方法,该FSM识别与此正则表达式匹配的列表(如果我没有犯任何错误 :)):
type alphabet = A | B | C | D
let rec s1 = function
| C :: rest -> s2 rest
| _ -> false
and s2 = function
| [] -> true
| (A | B) :: rest -> s2 rest
| C :: rest -> s3 rest
| _ -> false
and s3 = function
| D :: rest -> s2 rest
| _ -> false
每个函数对应于自动机的一个状态,并实现其转换函数。应用 s1 : alphabet list -> bool
将在参数上运行FSM。type event = string
module EventMap = Map.Make(struct
type t = event
let compare = compare
end)
type state = {
state_info : ...; (* the content of that state, id, comment, etc. *)
mutable state_transitions : state EventMap.t;
}
let next_state current_state event =
try
EventMap.find event current_state.state_transitions
with Not_found -> current_state
在此,我假设未知事件保持在相同的状态,但您可能会在记录中遇到错误状态...
(*********************************************************
* FSM testing *******************************************
*)
(* inputs to the FSM *)
let full = Var({name ="full"; value = F});;
let ten_minutes = Var({name = "ten_minutes"; value = F});;
let empty = Var({name = "empty"; value = F});;
let five_minutes = Var({name = "five_minutes"; value =F});;
(* T is true, F is false *)
let _ =
assign full F ;
assign ten_minutes F ;
assign empty F ;
assign five_minutes F ;;
(* outputs from the FSM *)
let water_on = Var({name = "water_on"; value = F});;
let agitate = Var({name = "agitate"; value = F});;
let drain = Var({name = "drain" ; value = F});;
let start_timer = Var({name = "start_timer"; value = F});;
let motor_on = Var({name = "motor_on"; value = F});;
let washed = Var({name = "washed"; value = F});;
let soap = Var({name = "soap"; value = F});;
let reset_actions =
assign water_on F;
assign agitate F;
assign drain F;
assign start_timer F;
assign motor_on F;;
module WashStates =
struct
type t = START | FILL | WASH | DRAIN | RINSE | SPIN | STOP
deriving(Show, Enum)
let start_state = START
end
module LogicExp =
struct
type t = boolean Logic.bexp
type var_t = boolean Logic.variable
let eval_exp exp = to_bool (Logic.eval exp)
let var_to_s = var_to_s
end
module WashFSM = FSM(WashStates)(LogicExp)
open WashStates
(* declare the state table *)
(* CS, PREDICATE, NS, ACTIONs *)
let my_fsm = [
(START, Const(T), FILL, [(water_on, T);
(soap, T)]);
(FILL, Bop(And,full,soap), WASH, [(water_on, F);
(agitate, T);
(washed, T);
(start_timer,T)]);
(WASH, ten_minutes, DRAIN,[(agitate, F);
(start_timer,F);
(empty, T)]);
(DRAIN, Bop(And,empty,soap), FILL, [(drain, F);
(soap, F);
(water_on, T)] );
(FILL, Bop(And,full,Not(soap)), RINSE,[(water_on, F);
(soap, F);
(empty, F);
(agitate, T)]);
(RINSE, ten_minutes, DRAIN, [(agitate, F);
(empty, T)] );
(DRAIN, Bop(And,empty,Not(soap)), SPIN, [(motor_on, T);
(start_timer,T)]);
(SPIN, five_minutes, STOP, [(water_on, F);
(drain, F);
(start_timer,F);
(motor_on, F)]);
(STOP, Const(T), STOP, [(motor_on, F)]);
];;
let st_table, current_state = WashFSM.create my_fsm in
let _ = assign full T in
let current_state = WashFSM.eval_fsm st_table current_state in
let _ = assign ten_minutes T in
let current_state = WashFSM.eval_fsm st_table current_state in
let current_state = WashFSM.eval_fsm st_table current_state in
let _ = (assign ten_minutes F);(assign empty T) in
let current_state = WashFSM.eval_fsm st_table current_state in
let _ = assign five_minutes T in
let current_state = WashFSM.eval_fsm st_table current_state in
let _ = assign five_minutes F in
let _ = assign ten_minutes T in
let current_state = WashFSM.eval_fsm st_table current_state in
let current_state = WashFSM.eval_fsm st_table current_state in
let _ = assign five_minutes T in
let _ = WashFSM.eval_fsm st_table current_state in
(*...and so on...*)
请原谅“;;”结尾 - 我想能够将此代码剪切并粘贴到REPL中
这里使用的一些代码可以在我的github上的Logic project中找到(fsm.ml是该项目的一部分)。 谓词表达式评估为T或F(真或假)。 如果为真,则从当前状态转换到下一个状态。 Const T表示始终转换。 例如:
Bop(And, full, soap)
如果full和soap都是T(真),则表达式的值为真。