arith_syntax.ml

type expression =
  | Numeral of float (** non-negative integer constant *)
  | Plus of expression * expression  (** Addition [e1 + e2] *)
  | Minus of expression * expression (** Difference [e1 - e2] *)
  | Times of expression * expression (** Product [e1 * e2] *)
  | Divide of expression * expression (** Quotient [e1 / e2] *)
  | Negate of expression (** Opposite value [-e] *)
  | Variable of string


let rec str e = 
  match e with 
  | Numeral  f -> string_of_float f 
  | Plus (a,b) -> str a ^ "+" ^ str b 
  | Minus (a,b) -> str a ^ "-" ^ str b 
  | Times (a,b) -> str a ^ "*" ^ str b 
  | Divide (a,b) -> str a ^ "/" ^ str b 
  | Negate a -> "-" ^ str a 
  | Variable s -> s