open Expr

let rec eval env = function
  | Const f -> f
  | SymConst Pi -> 4.0 *. atan 1.0
  | SymConst E -> exp 1.0
  | Var v ->
      (try List.assoc v env
       with Not_found -> failwith ("unbound variable: " ^ v))
  | Add (e1, e2) -> eval env e1 +. eval env e2
  | Sub (e1, e2) -> eval env e1 -. eval env e2
  | Mul (e1, e2) -> eval env e1 *. eval env e2
  | Div (e1, e2) -> eval env e1 /. eval env e2
  | Pow (e1, e2) -> eval env e1 ** eval env e2
  | Neg e -> -.(eval env e)
  | Sin e -> sin (eval env e)
  | Cos e -> cos (eval env e)
  | Tan e -> tan (eval env e)
  | Sinh e -> sinh (eval env e)
  | Cosh e -> cosh (eval env e)
  | Tanh e -> tanh (eval env e)
  | Asin e -> asin (eval env e)
  | Acos e -> acos (eval env e)
  | Atan e -> atan (eval env e)
  | Atan2 (e1, e2) -> atan2 (eval env e1) (eval env e2)
  | Exp e -> exp (eval env e)
  | Ln e -> log (eval env e)
  | Log (base_e, arg) ->
      let b = eval env base_e in
      let a = eval env arg in
      log a /. log b
  | Sqrt e -> sqrt (eval env e)
  | Abs e -> abs_float (eval env e)