1 files changed, 78 insertions, 0 deletions
diff --git a/plugins/syntax/nat_syntax.ml b/plugins/syntax/nat_syntax.ml
new file mode 100644
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+++ b/plugins/syntax/nat_syntax.ml
@@ -0,0 +1,78 @@
+(************************************************************************)
+(*  v      *   The Coq Proof Assistant  /  The Coq Development Team     *)
+(* <O___,, * CNRS-Ecole Polytechnique-INRIA Futurs-Universite Paris Sud *)
+(*   \VV/  **************************************************************)
+(*    //   *      This file is distributed under the terms of the       *)
+(*         *       GNU Lesser General Public License Version 2.1        *)
+(************************************************************************)
+
+(* $Id$ *)
+
+(* This file defines the printer for natural numbers in [nat] *)
+
+(*i*)
+open Pcoq
+open Pp
+open Util
+open Names
+open Coqlib
+open Rawterm
+open Libnames
+open Bigint
+open Coqlib
+open Notation
+open Pp
+open Util
+open Names
+(*i*)
+
+(**********************************************************************)
+(* Parsing via scopes *)
+(* For example, (nat_of_string "3") is <<(S (S (S O)))>> *)
+
+let nat_of_int dloc n =
+  if is_pos_or_zero n then begin
+      if less_than (of_string "5000") n then
+	Flags.if_warn msg_warning
+	  (strbrk "Stack overflow or segmentation fault happens when " ++
+	   strbrk "working with large numbers in nat (observed threshold " ++
+	   strbrk "may vary from 5000 to 70000 depending on your system " ++
+	   strbrk "limits and on the command executed).");
+      let ref_O = RRef (dloc, glob_O) in
+      let ref_S = RRef (dloc, glob_S) in
+      let rec mk_nat acc n =
+	if n <> zero then
+	  mk_nat (RApp (dloc,ref_S, [acc])) (sub_1 n)
+	else
+	  acc
+      in
+      mk_nat ref_O n
+    end
+  else
+      user_err_loc (dloc, "nat_of_int",
+        str "Cannot interpret a negative number as a number of type nat")
+
+(************************************************************************)
+(* Printing via scopes *)
+
+exception Non_closed_number
+
+let rec int_of_nat = function
+  | RApp (_,RRef (_,s),[a]) when s = glob_S -> add_1 (int_of_nat a)
+  | RRef (_,z) when z = glob_O -> zero
+  | _ -> raise Non_closed_number
+
+let uninterp_nat p =
+  try
+    Some (int_of_nat p)
+  with
+    Non_closed_number -> None
+
+(************************************************************************)
+(* Declare the primitive parsers and printers *)
+
+let _ =
+  Notation.declare_numeral_interpreter "nat_scope"
+    (nat_path,["Coq";"Init";"Datatypes"])
+    nat_of_int
+    ([RRef (dummy_loc,glob_S); RRef (dummy_loc,glob_O)], uninterp_nat, true)