diff --git a/tiramisu/autolib.py b/tiramisu/autolib.py
index c6d3e79..17c8a67 100644
--- a/tiramisu/autolib.py
+++ b/tiramisu/autolib.py
@@ -43,6 +43,8 @@ def carry_out_calculation(name, config, callback, callback_params):
     for key, values in callback_params.items():
         for value in values:
             if type(value) == tuple:
+                if config is None:
+                    raise ConfigError(_('no config specified but needed'))
                 path, check_disabled = value
                 try:
                     opt_value = config._getattr(path, force_permissive=True)
@@ -108,13 +110,4 @@ def carry_out_calculation(name, config, callback, callback_params):
 
 
 def calculate(name, callback, params, tcparams):
-    try:
-        # XXX not only creole...
-        from creole import eosfunc
-        return getattr(eosfunc, callback)(*params, **tcparams)
-    except AttributeError, err:
-        import traceback
-        traceback.print_exc()
-        raise ConfigError("callback: {0} return error {1} for "
-                          "option: {2}".format(callback, str(err),
-                                               name))
+    return callback(*params, **tcparams)
diff --git a/tiramisu/error.py b/tiramisu/error.py
index bf9c398..95c5b7c 100644
--- a/tiramisu/error.py
+++ b/tiramisu/error.py
@@ -24,6 +24,7 @@
 #           or if not logical
 #           or if validation failled
 #           or multi must be a list
+#           or error in autolib
 #TypeError if parameter has no good type
 #AttributeError if no option or optiondescription in optiondescription (also when specified a path)
 
diff --git a/tiramisu/option.py b/tiramisu/option.py
index 01409ed..9a11e0d 100644
--- a/tiramisu/option.py
+++ b/tiramisu/option.py
@@ -21,13 +21,14 @@
 # the whole pypy projet is under MIT licence
 # ____________________________________________________________
 import re
-from copy import copy
+from copy import copy, deepcopy
 from types import FunctionType
 from IPy import IP
 
 from tiramisu.error import ConflictError
 from tiramisu.setting import groups, multitypes
 from tiramisu.i18n import _
+from tiramisu.autolib import carry_out_calculation
 
 name_regexp = re.compile(r'^\d+')
 forbidden_names = ['iter_all', 'iter_group', 'find', 'find_fisrt',
@@ -138,8 +139,8 @@ class Option(BaseInformation):
             raise ValueError(_("params defined for a callback function but "
                              "no callback defined yet for option {0}").format(name))
         if callback is not None:
-            if not isinstance(callback, str):
-                raise ValueError('callback must be a string')
+            if type(callback) != FunctionType:
+                raise ValueError('callback must be a function')
             if callback_params is not None and \
                     not isinstance(callback_params, dict):
                 raise ValueError('callback_params must be a dict')
@@ -176,6 +177,22 @@ class Option(BaseInformation):
         :param value: the option's value
         :param validate: if true enables ``self._validator`` validation
         """
+        def _val_validator(val):
+            callback_params = deepcopy(self._validator[1])
+            callback_params.setdefault('', []).insert(0, val)
+            return carry_out_calculation(self._name, config=context,
+                                         callback=self._validator[0],
+                                         callback_params=callback_params)
+
+        def val_validator():
+            #add current value has first argument
+            if self.optimpl_is_multi():
+                for val in value:
+                    if not _val_validator(val):
+                        return False
+            else:
+                return _val_validator(val)
+            return True
         # generic calculation
         if context is not None:
             cons = context.cfgimpl_get_description()
@@ -203,11 +220,14 @@ class Option(BaseInformation):
                 if val is not None:
                     # customizing the validator
                     if validate and self._validator is not None and \
-                            not self._validator[0](val, **self._validator[1]):
+                            not val_validator():
                         return False
                     if not self._validate(val):
                         return False
-                    if cons is not None and not cons._valid_consistency(self, val, context, index):
+                    if cons is not None and not cons._valid_consistency(self,
+                                                                        val,
+                                                                        context,
+                                                                        index):
                         return False
         return True
 
@@ -308,6 +328,12 @@ class ChoiceOption(Option):
                                            validator_args=validator_args,
                                            properties=properties)
 
+    def optimpl_get_values(self):
+        return self._values
+
+    def optimpl_is_openvalues(self):
+        return self._open_values
+
     def _validate(self, value):
         if not self._open_values:
             return value is None or value in self._values