type expr =
  | Number of float
  | Add of expr * expr
  | Sub of expr * expr
  | Mul of expr * expr
  | Div of expr * expr
  | Mod of expr * expr
  | Exp of expr * expr
[@@deriving show]

and stat =
  | Let of string * expr
[@@deriving show]

and stat_or_expr =
  | Expr of expr
  | Stat of stat
[@@deriving show]

and prog =
  | Program of stat_or_expr list
[@@deriving show]

let s tree = show tree
let sp tree = show_prog prog
let p = pp tree
let pp = pp_prog tree