src/Pure/Isar/parse.scala

--- a/src/Pure/Isar/parse.scala	Thu Jul 19 14:15:08 2012 +0200
+++ b/src/Pure/Isar/parse.scala	Thu Jul 19 14:24:40 2012 +0200
@@ -54,6 +54,7 @@
         tok => tok.kind == Token.Kind.KEYWORD && tok.content == name)
 
     def string: Parser[String] = atom("string", _.is_string)
+    def nat: Parser[Int] = atom("natural number", _.is_nat) ^^ (s => Integer.parseInt(s))
     def name: Parser[String] = atom("name declaration", _.is_name)
     def xname: Parser[String] = atom("name reference", _.is_xname)
     def text: Parser[String] = atom("text", _.is_text)