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|
type ('var, 'binder) term =
| TVar of 'var
| TAbs of 'binder * ('var, 'binder) term
| TApp of ('var, 'binder) term * ('var, 'binder) term
[@@deriving
visitors { variety = "iter" },
visitors { variety = "map" },
visitors { variety = "reduce" },
visitors { variety = "endo" },
visitors { variety = "iter2" },
visitors { variety = "map2" },
visitors { variety = "reduce2" }
]
(* Nominal. *)
module StringSet = Set.Make(String)
let iter = object(self)
inherit [_] iter
(* Descending methods for local types. *)
method! visit_TAbs env x t =
let env = StringSet.add x env in
self#visit_term env t
(* Descending methods for nonlocal types. *)
method visit_'binder _env _x = ()
method visit_'var env x =
if StringSet.mem x env then
Printf.printf "%s is a bound variable.\n%!" x
else
Printf.printf "%s is a free variable.\n%!" x
end
let t : (_, _) term =
TAbs ("x", TApp (TVar "x", TVar "y"))
let () =
iter#visit_term StringSet.empty t
(* De Bruijn. *)
let iter = object(self)
inherit [_] iter
(* Descending methods for local types. *)
method! visit_TAbs env _x t =
let env = 1 + env in
self#visit_term env t
(* Descending methods for nonlocal types. *)
method visit_'binder _env _x = ()
method visit_'var env x =
if x < env then
Printf.printf "%d is a bound variable.\n%!" x
else
Printf.printf "%d is a free variable.\n%!" x
end
let t : (_, _) term =
TAbs ((), TApp (TVar 0, TVar 1))
let () =
iter#visit_term 0 t
|
