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|
(* $Id$ *)
(* This file to allow writing (3) for (S (S (S O)))
and still write (S y) for (S y) *)
open Pcoq
open Pp
open Util
open Names
open Coqast
open Ast
exception Non_closed_number
let get_nat_sign loc =
let ast_of_id id = Astterm.globalize_command (Nvar(loc,id)) in
(ast_of_id "O", ast_of_id "S", ast_of_id "My_special_variable")
(* For example, (nat_of_string "3") is <<(S (S (S O)))>> *)
let nat_of_int n dloc =
let (astO,astS,_) = get_nat_sign dloc in
let rec mk_nat n =
if n <= 0 then
astO
else
Node(dloc,"APPLIST", [astS; mk_nat (n-1)])
in
mk_nat n
let nat_of_string s dloc =
nat_of_int (int_of_string s) dloc
let rec int_of_nat_rec astS astO p =
match p with
| Node (_,"APPLIST", [b; a]) when alpha_eq(b,astS) ->
(int_of_nat_rec astS astO a)+1
| a when alpha_eq(a,astO) -> 1
(***** YES, 1, non 0 ... to print the successor of p *)
| _ -> raise Non_closed_number
let int_of_nat p =
let (astO,astS,_) = get_nat_sign dummy_loc in
try
Some (int_of_nat_rec astS astO p)
with
Non_closed_number -> None
let replace_S p =
let (_,astS,astmyvar) = get_nat_sign dummy_loc in
let rec aux p =
match p with
| Node (l,"APPLIST", [b; a]) when b = astS ->
Node (l, "APPLIST", [astmyvar; (aux a)])
| _ -> p
in
ope("APPLIST", [astmyvar; (aux p)])
(* Declare the primitive printer *)
(* Prints not p, but the SUCCESSOR of p !!!!! *)
let nat_printer std_pr p =
match (int_of_nat p) with
| Some i -> [< 'sTR (string_of_int i) >]
| None -> std_pr (replace_S p)
let _ = Esyntax.Ppprim.add ("nat_printer", nat_printer)
(* Declare the primitive parser *)
let number =
match create_entry (get_univ "nat") "number" ETast with
| Ast n -> n
| _ -> anomaly "G_natsyntax : create_entry number failed"
let _ =
Gram.extend number None
[None, None,
[[Gramext.Stoken ("INT", "")],
Gramext.action nat_of_string]]
|
