Index: TODO
===================================================================
diff -u -r761c9758221eb84b88a328e659523c4773aa5dfe -rb6d81c6521d1e1d58f00763f5ab30a0946cc222a
--- TODO	(.../TODO)	(revision 761c9758221eb84b88a328e659523c4773aa5dfe)
+++ TODO	(.../TODO)	(revision b6d81c6521d1e1d58f00763f5ab30a0946cc222a)
@@ -1245,6 +1245,12 @@
 - added flag -complain to ::nsf::is
 - removed ::nsf::parametercheck
 
+- new parameter option "convert" to signal that an application
+  specific parameter checker should convert the value 
+  (takes the result of the methods as conversion result)
+- added parameters for slots "allowemtpy" and "convert"
+- extended regression test
+
 TODO: 
 - reflect changes in /is/objectproperty/info has/info is/ in migration guide
 - implement built-in-converter for "baseclass" and "metaclass"?
Index: generic/xotcl.c
===================================================================
diff -u -r761c9758221eb84b88a328e659523c4773aa5dfe -rb6d81c6521d1e1d58f00763f5ab30a0946cc222a
--- generic/xotcl.c	(.../xotcl.c)	(revision 761c9758221eb84b88a328e659523c4773aa5dfe)
+++ generic/xotcl.c	(.../xotcl.c)	(revision b6d81c6521d1e1d58f00763f5ab30a0946cc222a)
@@ -5439,6 +5439,9 @@
       if ((pPtr->flags & XOTCL_ARG_ALLOW_EMPTY)) {
         ParamDefsFormatOption(interp, nameStringObj, "allowempty", &colonWritten, &first);
       }
+      if ((pPtr->flags & XOTCL_ARG_IS_CONVERTER)) {
+        ParamDefsFormatOption(interp, nameStringObj, "convert", &colonWritten, &first);
+      }
       if ((pPtr->flags & XOTCL_ARG_INITCMD)) {
         ParamDefsFormatOption(interp, nameStringObj, "initcmd", &colonWritten, &first);
       } else if ((pPtr->flags & XOTCL_ARG_METHOD)) {
@@ -6534,19 +6537,22 @@
   DECR_REF_COUNT(ov[1]);
   DECR_REF_COUNT(ov[2]);
 
+  *outObjPtr = objPtr;
+    
   if (result == TCL_OK) {
     /*fprintf(stderr, "convertViaCmd converts %s to '%s' paramPtr %p\n", 
       ObjStr(objPtr), ObjStr(Tcl_GetObjResult(interp)),pPtr);*/
-    *outObjPtr = Tcl_GetObjResult(interp);
+    if (pPtr->flags & XOTCL_ARG_IS_CONVERTER) {
+      /*
+       * If we want to convert, the resulting obj is the result of the
+       * converter. incr refCount is necessary e.g. for e.g.
+       *     return [expr {$value + 1}]
+       */
+      *outObjPtr = Tcl_GetObjResult(interp);
+      INCR_REF_COUNT(*outObjPtr);   
+    }
     *clientData = (ClientData) *outObjPtr;
-
-    /* incr refCount is necessary e.g. for 
-       return [expr {$value + 1}]
-    */
-    INCR_REF_COUNT(*outObjPtr);   
-  } else {
-    *outObjPtr = objPtr;
-  }
+  } 
   return result;
 }
 
@@ -6615,6 +6621,8 @@
     paramPtr->flags |= XOTCL_ARG_SUBST_DEFAULT;
   } else if (strncmp(option, "allowempty", 10) == 0) {
     paramPtr->flags |= XOTCL_ARG_ALLOW_EMPTY;
+  } else if (strncmp(option, "convert", 7) == 0) {
+    paramPtr->flags |= XOTCL_ARG_IS_CONVERTER;
   } else if (strncmp(option, "initcmd", 7) == 0) {
     paramPtr->flags |= XOTCL_ARG_INITCMD;
   } else if (strncmp(option, "method", 6) == 0) {
@@ -6859,10 +6867,14 @@
         result = ParamOptionSetConverter(interp, paramPtr, converterNameString, convertViaCmd);
       }
     }
+    if ((paramPtr->flags & XOTCL_ARG_IS_CONVERTER) && paramPtr->converter != convertViaCmd) {
+      return XOTclVarErrMsg(interp, 
+                            "option 'convert' only allowed for application-defined converters",
+                            (char *) NULL);
+    }
     if (converterNameObj != paramPtr->converterName) {
       DECR_REF_COUNT(converterNameObj);
     }
-    
   }
 
   /*
Index: generic/xotclInt.h
===================================================================
diff -u -rd2f17f8dd98fcfa82a8473ed5e299c7c2026a80f -rb6d81c6521d1e1d58f00763f5ab30a0946cc222a
--- generic/xotclInt.h	(.../xotclInt.h)	(revision d2f17f8dd98fcfa82a8473ed5e299c7c2026a80f)
+++ generic/xotclInt.h	(.../xotclInt.h)	(revision b6d81c6521d1e1d58f00763f5ab30a0946cc222a)
@@ -374,12 +374,13 @@
 #define XOTCL_ARG_RELATION		     0x0100
 #define XOTCL_ARG_SWITCH		     0x0200
 #define XOTCL_ARG_HAS_DEFAULT		     0x1000
+#define XOTCL_ARG_IS_CONVERTER		     0x2000
 
 /* disallowed options */
 #define XOTCL_DISALLOWED_ARG_METHOD_PARAMETER	     (XOTCL_ARG_METHOD|XOTCL_ARG_INITCMD|XOTCL_ARG_RELATION)
 #define XOTCL_DISALLOWED_ARG_SETTER	     	     (XOTCL_ARG_SUBST_DEFAULT|XOTCL_DISALLOWED_ARG_METHOD_PARAMETER)
 #define XOTCL_DISALLOWED_ARG_OBJECT_PARAMETER	     0
-#define XOTCL_DISALLOWED_ARG_VALUEECHECK	     (XOTCL_ARG_SUBST_DEFAULT|XOTCL_ARG_METHOD|XOTCL_ARG_INITCMD|XOTCL_ARG_RELATION|XOTCL_ARG_SWITCH|XOTCL_ARG_CURRENTLY_UNKNOWN)
+#define XOTCL_DISALLOWED_ARG_VALUEECHECK	     (XOTCL_ARG_SUBST_DEFAULT|XOTCL_ARG_METHOD|XOTCL_ARG_INITCMD|XOTCL_ARG_RELATION|XOTCL_ARG_SWITCH|XOTCL_ARG_CURRENTLY_UNKNOWN|XOTCL_ARG_IS_CONVERTER)
 
 
 /* method types */
Index: library/nx/nx.tcl
===================================================================
diff -u -rf20a7f81bcae20a40c4990afd431615ca1914c51 -rb6d81c6521d1e1d58f00763f5ab30a0946cc222a
--- library/nx/nx.tcl	(.../nx.tcl)	(revision f20a7f81bcae20a40c4990afd431615ca1914c51)
+++ library/nx/nx.tcl	(.../nx.tcl)	(revision b6d81c6521d1e1d58f00763f5ab30a0946cc222a)
@@ -1294,6 +1294,12 @@
       lappend objopts $prefix=${:arg}
       lappend methodopts $prefix=${:arg}
     }
+    foreach att {convert allowempty} {
+      if {[info exists :$att]} {
+	lappend objopts $att
+	lappend methodopts $att
+      }
+    }
     if {[info exists :default]} {
       set arg ${:default}
       # deactivated for now: || [string first {$} $arg] > -1
@@ -1617,6 +1623,8 @@
     valuecmd
     valuechangedcmd
     arg
+    allowempty
+    convert
   }
 
   Attribute method __default_from_cmd {obj cmd var sub op} {
Index: library/xotcl/tests/slottest.xotcl
===================================================================
diff -u -r76fadfb3f603f8f96a6064f4bb5342133923ec53 -rb6d81c6521d1e1d58f00763f5ab30a0946cc222a
--- library/xotcl/tests/slottest.xotcl	(.../slottest.xotcl)	(revision 76fadfb3f603f8f96a6064f4bb5342133923ec53)
+++ library/xotcl/tests/slottest.xotcl	(.../slottest.xotcl)	(revision b6d81c6521d1e1d58f00763f5ab30a0946cc222a)
@@ -408,7 +408,7 @@
 ? {p2 salary} 1009
 
 Person slots {
-  Attribute create sex -type "sex" {
+  Attribute create sex -type "sex" -convert true {
     :method type=sex {name value} {
       #puts stderr "[self] slot specific converter"
       switch -glob $value {
@@ -421,7 +421,7 @@
 }
 Person p3 -sex male
 ? {p3 sex} m
-Person method foo {s:sex,slot=::Person::slot::sex} {return $s}
+Person method foo {s:sex,slot=::Person::slot::sex,convert} {return $s}
 ? {p3 foo male} "m"
 ? {p3 sex male} m
 
Index: tests/parameters.tcl
===================================================================
diff -u -r4dc0f6d2bab7c95b74c346604e63cecec770f8fc -rb6d81c6521d1e1d58f00763f5ab30a0946cc222a
--- tests/parameters.tcl	(.../parameters.tcl)	(revision 4dc0f6d2bab7c95b74c346604e63cecec770f8fc)
+++ tests/parameters.tcl	(.../parameters.tcl)	(revision b6d81c6521d1e1d58f00763f5ab30a0946cc222a)
@@ -77,6 +77,9 @@
   ? {::nsf::is switch 1} {invalid value constraints "switch"}
   ? {::nsf::is superclass M} {invalid value constraints "superclass"}
 
+  # don't allow convert
+  ? {::nsf::is integer,convert 1} {invalid value constraints "integer,convert"}
+
   # tcl checker
   ? {::nsf::is upper ABC} 1
   ? {::nsf::is upper Abc} 0
@@ -933,11 +936,12 @@
     }
   }
   Class create C {
-    :method foo {s:sex,multivalued} {return $s}
+    :method foo {s:sex,multivalued,convert} {return $s}
+    :method bar {s:sex,multivalued} {return $s}
   }
   C create c1
   ? {c1 foo {male female mann frau}} "m f m f"
-  
+  ? {c1 bar {male female mann frau}} "male female mann frau"
 
   Object create tmpObj
   tmpObj method type=mType {name value arg:optional} {
@@ -966,7 +970,7 @@
     }
   }
   Object create o {
-    :method foo {x:integer,slot=::mySlot} {
+    :method foo {x:integer,slot=::mySlot,convert} {
       return $x
     }
   }
@@ -1012,6 +1016,7 @@
   Class create Person {
     :attribute sex {
       :type "sex"
+      :convert true
       :method type=sex {name value} {
 	#puts stderr "[self] slot specific converter"
 	switch -glob $value {
@@ -1025,7 +1030,7 @@
 
   Person create p1 -sex male
   ? {p1 sex} m
-  Person method foo {s:sex,slot=::Person::slot::sex} {return $s}
+  Person method foo {s:sex,slot=::Person::slot::sex,convert} {return $s}
   ? {p1 foo male} m
   ? {p1 sex male} m
 }