type aexpr =
    | CstI of int
    | Var of string
    | Add of aexpr * aexpr
    | Mul of aexpr * aexpr
    | Sub of aexpr * aexpr;;

// Sub(Var "v", Add(Var "w", Var "z"));;
// Mul(CstI 2, Sub(Var "v", Add(Var "w", Var "z"));;
// Add(Var "x", Add(Var "y", Add(Var "z", Var "v")));;

let rec fmt ae : string =
    match ae with
    | CstI i -> i.ToString()
    | Var x -> x
    | Add(ae1, ae2) -> "(" + fmt(ae1) + " + " + fmt(ae2) + ")"
    | Mul(ae1, ae2) -> "(" + fmt(ae1) + " * " + fmt(ae2) + ")"
    | Sub(ae1, ae2) -> "(" + fmt(ae1) + " - " + fmt(ae2) + ")";;