clarified modules;

--- a/src/Pure/General/symbol_pos.ML	Thu Mar 31 15:42:01 2016 +0200
+++ b/src/Pure/General/symbol_pos.ML	Thu Mar 31 16:23:25 2016 +0200
@@ -46,6 +46,8 @@
   val explode0: string -> T list
   val scan_ident: T list -> T list * T list
   val is_identifier: string -> bool
+  val scan_nat: T list -> T list * T list
+  val scan_float: T list -> T list * T list
 end;
 
 structure Symbol_Pos: SYMBOL_POS =
@@ -300,6 +302,12 @@
       SOME (_, []) => true
     | _ => false);
 
+
+(* numerals *)
+
+val scan_nat = Scan.many1 (Symbol.is_digit o symbol);
+val scan_float = scan_nat @@@ $$$ "." @@@ scan_nat;
+
 end;
 
 structure Basic_Symbol_Pos =   (*not open by default*)

--- a/src/Pure/Isar/token.ML	Thu Mar 31 15:42:01 2016 +0200
+++ b/src/Pure/Isar/token.ML	Thu Mar 31 16:23:25 2016 +0200
@@ -620,8 +620,8 @@
         Lexicon.scan_var >> pair Var ||
         Lexicon.scan_tid >> pair Type_Ident ||
         Lexicon.scan_tvar >> pair Type_Var ||
-        Lexicon.scan_float >> pair Float ||
-        Lexicon.scan_nat >> pair Nat ||
+        Symbol_Pos.scan_float >> pair Float ||
+        Symbol_Pos.scan_nat >> pair Nat ||
         scan_symid >> pair Sym_Ident) >> uncurry token));
 
 fun recover msg =

--- a/src/Pure/Syntax/lexicon.ML	Thu Mar 31 15:42:01 2016 +0200
+++ b/src/Pure/Syntax/lexicon.ML	Thu Mar 31 16:23:25 2016 +0200
@@ -15,8 +15,6 @@
   val scan_id: Symbol_Pos.T list -> Symbol_Pos.T list * Symbol_Pos.T list
   val scan_longid: Symbol_Pos.T list -> Symbol_Pos.T list * Symbol_Pos.T list
   val scan_tid: Symbol_Pos.T list -> Symbol_Pos.T list * Symbol_Pos.T list
-  val scan_nat: Symbol_Pos.T list -> Symbol_Pos.T list * Symbol_Pos.T list
-  val scan_float: Symbol_Pos.T list -> Symbol_Pos.T list * Symbol_Pos.T list
   val scan_hex: Symbol_Pos.T list -> Symbol_Pos.T list * Symbol_Pos.T list
   val scan_bin: Symbol_Pos.T list -> Symbol_Pos.T list * Symbol_Pos.T list
   val scan_var: Symbol_Pos.T list -> Symbol_Pos.T list * Symbol_Pos.T list
@@ -96,13 +94,11 @@
 val scan_longid = scan_id @@@ Scan.repeats1 ($$$ "." @@@ scan_id);
 val scan_tid = $$$ "'" @@@ scan_id;
 
-val scan_nat = Scan.many1 (Symbol.is_digit o Symbol_Pos.symbol);
-val scan_float = scan_nat @@@ $$$ "." @@@ scan_nat;
 val scan_hex = $$$ "0" @@@ $$$ "x" @@@ Scan.many1 (Symbol.is_ascii_hex o Symbol_Pos.symbol);
 val scan_bin = $$$ "0" @@@ $$$ "b" @@@ Scan.many1 (fn (s, _) => s = "0" orelse s = "1");
-val scan_num = scan_hex || scan_bin || scan_nat;
+val scan_num = scan_hex || scan_bin || Symbol_Pos.scan_nat;
 
-val scan_id_nat = scan_id @@@ Scan.optional ($$$ "." @@@ scan_nat) [];
+val scan_id_nat = scan_id @@@ Scan.optional ($$$ "." @@@ Symbol_Pos.scan_nat) [];
 val scan_var = $$$ "?" @@@ scan_id_nat;
 val scan_tvar = $$$ "?" @@@ $$$ "'" @@@ scan_id_nat;
 
@@ -264,7 +260,7 @@
       scan_tvar >> token TVarSy ||
       scan_var >> token VarSy ||
       scan_tid >> token TFreeSy ||
-      scan_float >> token FloatSy ||
+      Symbol_Pos.scan_float >> token FloatSy ||
       scan_num >> token NumSy ||
       scan_longid >> token LongIdentSy ||
       scan_xid >> token IdentSy;
@@ -310,7 +306,7 @@
 
     val scan =
       (scan_id >> map Symbol_Pos.symbol) --
-      Scan.optional ($$ "." |-- scan_nat >> (nat 0 o map Symbol_Pos.symbol)) ~1;
+      Scan.optional ($$ "." |-- Symbol_Pos.scan_nat >> (nat 0 o map Symbol_Pos.symbol)) ~1;
   in
     scan >>
       (fn (cs, ~1) => chop_idx (rev cs) []
@@ -357,7 +353,7 @@
 
 fun nat cs =
   Option.map (#1 o Library.read_int o map Symbol_Pos.symbol)
-    (Scan.read Symbol_Pos.stopper scan_nat cs);
+    (Scan.read Symbol_Pos.stopper Symbol_Pos.scan_nat cs);
 
 in