--- reg
+++ reg
@@ -65,4 +65,7 @@
 <token: number>
   (?:  (?: <minus> )? <int> (?: <frac> )?  (?: <exp> )?  )
+  (?{
+    $MATCH = join'', grep defined, map{$MATCH{$_}} qw{ minus int frac exp };
+  })
 
 <token: decimal_point>