(* IMP variable names are represented as strings *)
type varname = string

(* IMP arithmetic expressions *)
type iarith =
        Const of int
      | Var of varname
      | Plus of (iarith * iarith)
      | Minus of (iarith * iarith)
      | Times of (iarith * iarith)

(* IMP boolean expressions *)
type ibool =
        True
      | False
      | Leq of (iarith * iarith)
      | Conj of (ibool * ibool)
      | Disj of (ibool * ibool)
      | Neg of ibool

(* IMP commands *)
type icmd =
        Skip
      | Seq of (icmd * icmd)
      | Assign of (varname * iarith)
      | Cond of (ibool * icmd * icmd)
      | While of (ibool * icmd)