open Ast

let intop f a b =
  match a, b with
  | Int a, Int b -> Int (f a b)
  | _ -> failwith "typecheck failed"

let binop_to_func = function
  | Add -> intop Int.add
  | Sub -> intop Int.sub
  | Mul -> intop Int.mul
  | Div -> intop Int.div

let rec eval = function
  | Value v -> v
  | Binop (l, op, r) ->
    let f = binop_to_func op in
    f (eval l) (eval r)
  | Set_binop_pre (op, l) ->
    let l = match eval l with Int n -> n | _ -> failwith "not int" in 
    Hashtbl.replace Parser.precedence (Ast.binop_to_string op) l;
    Unit