env1.sml

(*Used when trying to look up a name that doesn't exist*)
exception NameNotBound of string;

(*Used to store the list of current bindings, each with a var name and value*)
type Env = (string * int) list;

(*Creates an empty environment*)
fun env_new () : Env = nil;

(*Adds a new element with the given name and value to the front of the given Env list*)
fun env_bind (e : Env) name num : Env = (name, num) :: e;

(*Looks up the value of a given name in the given Env
  Raises NameNotBound exception if name not found in the given Env*)
fun env_lookup (nil : Env) name = raise NameNotBound name
	| env_lookup (e: Env) name = if name = #1 (hd e) then #2 (hd e) else env_lookup (tl e) name;