3 type env = char -> bound
5 module R_E = Monad.Reader(E)
9 let env0 = fun var -> raise Not_found
10 let insert var value e = fun sought -> if sought = var then value else e sought
12 let getint (var : char) : int R.t = R.asks (fun e -> let x = e var in x)
14 (* monadic versions of `x` and `y` *)
18 (* monadic version of `y + x` *)
19 let (expr1 : int R.t) = R.(gety >>= fun y -> getx >>= fun x -> mid (y + x))
21 let (expr1 : int R.t) = R.(map2 (+) gety getx)
23 (* monadic version of `3 + x` *)
24 let (expr2 : int R.t) = R.(map2 (+) (mid 3) getx)
26 let letx xx body = R.(xx >>= fun x -> shift (insert 'x' x) body)
28 (* monadic version of `let x = 2 in 3 + x` *)
29 let (expr3 : int R.t) = R.(letx (mid 2) expr2)
31 let res = R.run expr3 env0 (* will be 5 *)