(* This example shows that the definition of FOO that is nested inside
   the (multi-line) definition of BAR affects only the body of the
   definition of BAR. It does not affect the text that follows a call
   to BAR. So, a multi-line macro definition acts as a scope delimiter. *)

#def BAR
  #define FOO "definition of FOO inside BAR"
  FOO (* expands to "definition of FOO inside BAR" *)
#enddef
#define FOO "definition of FOO at the top level"
FOO (* expands to "definition of FOO at the top level" *)
BAR
FOO (* expands to "definition of FOO at the top level" *)

(* If one wishes to delimit a scope, without actually defining a macro,
   one can use #scope ... #endscope. *)

#scope
  #define HELLO "first definition of HELLO"
  HELLO (* expands to "first definition of HELLO" *)
#endscope
#scope
  #define HELLO "second definition of HELLO"
  HELLO (* expands to "second definition of HELLO" *)
#endscope
HELLO (* this does not expand *)

(* The effect of #scope ... #endscope can be simulated by writing
   #def DUMMY ... #enddef DUMMY #undef DUMMY
   but this is a bit unnatural. *)

#def DUMMY
  #define HELLO "definition of HELLO inside the scope"
  HELLO (* expands to "definition of HELLO inside the scope" *)
#enddef
DUMMY
#undef DUMMY
HELLO (* this does not expand *)

(* Another simple example. *)

#scope
#define HI "I am defined"
let x = HI (* expands to "I am defined" *)
#endscope
#define HI 42
let y = HI (* expands to 42 *)

(* Check that the effect of #undef is also local.
   This example relies on the above definition of HI. *)

#scope
#undef HI
let qwd = HI (* HI is not recognized as a macro and expands to itself *)
#endscope
let z = HI (* expands to 42 *)

(* Scopes can be nested. *)

#define LEVEL 0
let x = LEVEL (* expands to 0 *)
#scope
  #undef LEVEL
  #define LEVEL 1
  let y = LEVEL (* expands to 1 *)
  #scope
    #undef LEVEL
    #define LEVEL 2
    let z = LEVEL (* expands to 2 *)
  #endscope
  let _ = LEVEL (* expands to 1 *)
#endscope
let _ = LEVEL (* expands to 0 *)

(* Another example of nesting. *)

#scope
  #define HELLO "Hello, "
  #scope
    #define MAN "man"
    let message1 = HELLO ^ MAN
  #endscope
  (* Here, MAN is no longer defined, but HELLO still is. *)
  let message2 = HELLO ^ "world"
#endscope