deno

let rec simplify e =
  match e with
  | CstI(i) -> CstI(i)
  | Var(x) -> Var(x)
  | Prim("+", e1, e2) -> if simplify e1 = CstI(0) then simplify e2 else
                         if simplify e2 = CstI(0) then simplify e1 else
                         Prim("+", simplify e1, simplify e2)