2 type bound = Int of int | Fun of (int R.t -> int R.t)
3 type env = char -> bound
5 and R : Monad.READER with type env = E.env = struct
7 module R_E = Monad.Reader(E)
12 let env0 = fun var -> raise Not_found
13 let insert var value e = fun sought -> if sought = var then value else e sought
15 let getint (var : char) = R.asks (fun e -> let (E.Int x) = e var in x)
17 let getfun (var : char) = R.asks (fun e -> let (E.Fun f) = e var in f)
19 (* monadic versions of `x` and `y` and `f` *)
24 (* monadic version of `y + x` *)
25 let (expr1 : int R.t) = R.(map2 (+) gety getx)
27 (* monadic version of `\y -> y + x` *)
28 let lambda1 = R.(fun yy -> yy >>= fun y -> shift (insert 'y' (E.Int y)) expr1)
30 let letx xx body = R.(xx >>= fun x -> shift (insert 'x' (E.Int x)) body)
31 let letf ff body = R.(ff >>= fun f -> shift (insert 'f' (E.Fun f)) body)
33 (* monadic version of `let x = 2 in let f = \y -> y + x in f 3` *)
34 let (expr4 : int R.t) = R.(letx (mid 2) (letf (mid lambda1) (getf >>= fun f -> f (mid 3))))
36 let res = R.run expr4 env0 (* will be 5 *)